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This is to certify that the

dissertation entitled

SYNTHESIS, MODELING AND CHARACTERIZATION OF
ETHYLENE OXIDE-SEGMENTED MICROBLOCK
COPOLYMERS

presented by

Yiyan Chen

has been accepted towards fulfillment
of the requirements for

Ph. D. degree in Chemistry

 

 

W2

l/Wajor rm of“

Date g//3/Q?

 

 

 

 

 

 

LIBRARY

Michigan State

University

 

 

PLACE IN RETURN BOX to remove this checkout from your record.
To AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE

DATE DUE

DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1m WWI-mu

 

 

 

SYNTHESIS.
EFdl'LENE OXlI

 

 

 

 

SYNTHESIS, MODELING AND CHARACTERIZATION OF
ETHYLENE OXIDE-SEGMENTED MICROBLOCK COPOLYMERS

By

Yiyan Chen

A DISSERTATION

Submitted to
Michigan State University
In partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Chemistry

1999

SlNTlfilSlS. MODE Ll

SEGX

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A t 'k". 4. . ,
1.1 31M. 15 Cllhtr a.
32:31:; a single tint;

9::;.:::;.2c.:e oxide «PL!

0.
'3 I. 2"

pile. The polym
‘liz‘b't'ienyhubstzmcd l
113598.0le Dill

.CTL‘E

4:3 -L

«214.1 of PEO scum

Pit ~-
u scgrncnts become 1'

113.33?" . -
p‘mCTSe-c
- cheats. the p.

8133“-
'~ L“-

d.

To Undfilxland Ib-

i'r- 'L
N‘ Us '30“
Us. -~
L lenc \tmkl 1‘“
K
3'3“:

ABSTRACT

SYNTHESIS, MODELING AND CHARACTERIZATION OF ETHYLENE OXIDE-

SEGMENTED MICROBLOCK COPOLYMERS
By

Yiyan Chen

We synthesized and characterized a series of (AB)n microblock copolymers where
the A block is either an exact length linear alkyl segment or a linear alkyl segment
containing a single double bond, and the B block is an exact length segment of
polyethylene oxide (PEO). Thus the A block is hydrophobic, and the B block is
hydrophilic. The polymers were prepared in high yields by metathesis polymerization of
mm—alkenyl—substituted PEOs. The polymers had number average molecular weights as
high as 98,000. Differential scanning calorimetry shows that the polymer Tgs increase as
the length of PEO segments increase when PEO segments is short, and level off when
PEO segments become longer. Above T3, the polymers exhibit a complicated sequence
of crystallization and melting transitions. Because of the amphiphilic nature of the
polymer segments, the polymers have good solubility in a variety of polar and nonpolar

solvents.

To understand the properties of the (AB)n polymers, a series of model compounds
with the generic structure H(CH2)X(OCH2CH2)yO(CH2)xH were synthesized. The melting
points of the model compounds show an odd-even effect when x S 12 and y S 6, with

compounds with odd values of y having higher melting points than oligomers with even

use of i". This Cm"

mas in he olignnicr

 

::::cu.i~ Mien ctr.) lcr
misc: he PEO scgm.

::::~i-:.~3~ .or studx the :

We .1ng frond il‘ “

In

'3': rue lads of ‘1th

 

 

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1:1; 1:14)} chums. Mt“

mtg-3n OI mxldi‘llali‘ 'i

5...: zxgzag confound:

Exit?“

. ,c
..om melt cm:

eig' ~ '
metal tontnmiatir

r145? 1""

' ‘
*‘L‘figs can ifivl

.93.. '
I :m‘O’
. _ 1.4
. “-I_ I,

. 3.416;)“ for incur

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u} . 3
‘5‘

. xgment lenzthx l

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be expcctm

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values of y. This effect can be traced to a planar trans conformation for the PEO
segments in the oligomers. Unsaturated polymers follow the same trend as the model
compounds when ethylene oxide segment is short while saturated polymers follow the
trend once the PEO segment is 2 3, which validates the use of these compounds as model

compounds for study the polymers.

We also found that crystalline model compounds with seven ethylene oxide units
have two kinds of structures: an extended planar zigzag form throughout the whole
molecule, and another having a helical ethylene oxide segment flanked by two planar
zigzag alkyl chains. More importantly, these conformations can be controlled by the
selection of crystallization method. Samples crystallized from polar solvents give the
planar zigzag conformation while samples crystallized from nonpolar solvent or fast
quenched from melt crystallize in a structure with planar conformations for alkyl chains
and a helical conformation for ethylene oxide segment. The structures of the saturated
polymer analogs can also be manipulated in the similar manner. This result points to a
general strategy for incorporating stable crystalline polymer sub-units into materials. By
using segment lengths that correspond to multiples of the polymer unit cell, such
segments can be expected to self-assemble into crystalline sub-units that have the same

structure as the parent polymer.

 

To my family

iv

[Mb (0 expreu
g.‘_'.ce. assixunee {hr-i x
xxx..- ziemor and a
23;: iso like to thank

Lil‘s-ting Chm»: and K:

 

31.33.71; member» lt
:3‘..\l.10. Gao. Micah. C

tartformakms mx 5

him calmed th;
filter hiding and \lA}

:0 ,‘f‘ A l .
--.~- m1} once a wan,

\.

«tar-w ,
.. me throuzhnu'
g .

Nam to thank n-

st—
L m“ Chen for hi

e. a
«ll; . ' '
:1) parents mnho'

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4 A‘AIL
he...
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19:31”:
“wm‘t‘nl.

ACKNOWLEDGEMENTS

I wish to express my deep appreciation to Professor Gregory L. Baker for his
guidance, assistance throughout the course of this research. He has been an excellent
academic mentor and a good friend, to whom I can always consult on a lot of issues. I
would also like to thank Professor Babak Borhan, Thomas Pinnavaia, Gary Blanchard,
Chi-Kwong Chang and Kris Berglund for their guidance and assistance. My thanks to all
Baker group members: Jun Qiao (my big Shil Xongl), Jun Hou, Jingpin, Sue, Cory,
Tara, Mao, Gao, Micah, Chun, JB, Tianqi, Kirk (sorry to leave you so much work), Erin

and Fadi for making my 5 years stay in the lab a memorable one.

I also enjoyed the life in Michigan — friendly people, cold winter and cool
summer (skiing and swimming), good environment (fishing, gardening, golfing —
though only once a year). I like to thank the Department of Chemistry for continuously

supporting me throughout the graduate study.

I want to thank my wife Yi for her constant love and support, my naughty son
Kevin Fakai Chen for his sacrifice to be away from parents at his very young age. I
thank my parents (without your push, I don’t know when I would finally start to pursue
this degree), my brother and my parents in law for their love, expectation and

encouragement.

i

lb'l 0T TlGl'RES ......
LIT 0F SCHEMILS......

USI OF TABLES m»

 

DTRODI'CTIO-V ...

1 General .

I Black CONT)'mCi pr

1. Phase \eparattnn i

1 C «9 ll. , -‘
. QsthZaIlUnm

H1 Iluitzple thermal tr;

1. General phaxe set

2. Lamellae thicken

3. Polymorphism

[I Smthesis of i AB 3:

' Chain Polymenz;

1 . . .
-. Ionic 1mm: poly!

3- Ste

pcopolymerll
4. -
lletahests poly-rt
S. -
.. C‘Ompanson oft:
“Hitters
'r .
gimme“

TABLE OF CONTENTS

 

 

 

 

LIST OF FIGURES - - ........... -- - . -- - - - x
LIST OF SCHEMES--- -- -- - - - - .......... - -- --.---xvii
LIST OF TABLES - - - - -- -- ..... - -- - - - - - xix
INTRODUCTION -- - ------ - - ............... - 1
I. General ...................................................................................................................... 1
11. Block copolymer properties ...................................................................................... 3
1. Phase separation and morphology .......................................................................... 3
2. Crystallization of polymers .................................................................................. 13
III. Multiple thermal transitions for polymers ............................................................... 17
1. General phase separated cases ............................................................................. 18
2. Lamellae thickening and thinning ........................................................................ 20
3. Polymorphism ...................................................................................................... 22
IV. Synthesis of (AB),, block Copolymers .................................................................... 26
1. Chain polymerization ........................................................................................... 26
2. Ionic living polymerization .................................................................................. 32
3. Step copolymerization .......................................................................................... 36
4. Metathesis polymerization ................................................................................... 38

5. Comparison of different polymerization methods for obtaining (AB)n
copolymers .................................................................................................................. 47
V. Target molecules in this research ............................................................................ 48

vi

ll Seterml polymers .1

 

l. Poliethylene any.
1 CE, nonlomc s..

3. lllctohloelt cop-

;{jgxlttethflcnc
4 Elortm'lxm-h}
RBI-14B WOOOOOOOC I
i Sjni'tests .tml punt.
l. Acronym forth:

I. Exact length clip

3. Tabioek amphtph
4

 

5. Polymers ..............
ll lie-penis of triblutl
l

1. Thermal behatlnr
‘ P
~ DuderX-rat tilt:

Spedroxcopte rim:

0

m , .
Properties of unxutut

males of filth" .
l Phl'sit-

VI. Several polymers directly related to this project ..................................................... 50

1. Polyethylene and polyethylene oxide .................................................................. 50
2. Cxl'iy nonionic surfactants and CxEOyCx amphiphilic triblock oligomers ............ 55
3. Microblock copolymers containing oligothioethylene, oligoethylene and
oligooxyethylene ........................................................................................................ S9
4. fluorocarbon-hydrocarbon microblock copolymers ............................................ 63
RESULTS ......................................................................................................................... 68
1. Synthesis and purification ....................................................................................... 68
l. Acronyms for the compounds in this research ..................................................... 68
2. Exact length oligoethylene glycols ...................................................................... 69
3. Triblock amphiphilic oligomers—model compounds ......................................... 71
4. Monomers ............................................................................................................ 72
5. Polymers ............................................................................................................... 76
11. Properties of triblock oligomers CxEoyCx .............................................................. 80
1. Thermal behavior ................................................................................................. 80
2. Powder X-ray diffraction ..................................................................................... 97
3. Spectroscopic characterizations ......................................................................... 115
H1. Properties of unsaturated (AB)n microblock copolymers (C,,1t:C,,EOy)n ................ 122
1. Physical properties ............................................................................................. 122
2. Morphologies of unsaturated polymers .............................................................. 124
3. Spectroscopic characterizations ......................................................................... 130
4. Thermal behavior of the unsaturated polymers .................................................. 132
5. XRD of unsaturated polymers ............................................................................ 147
IV. Properties of saturated (AB)n polymers (CxEOy)n ................................................. 153
1. Physical properties ............................................................................................. 153

vii

l llorphologyot’x
I
3. Thtl'illlll bk’hJVlt“

t. Spectroxcopre elzf
5. XRDresultst'or '~
DlStTSSlON ...............
l Suthesis and pun:

l. 51:1. esis of exat‘

' J

llortomer purrfit‘.

K's ‘
Point) changes

Pohmerizatron d:
H St". ~tr
are and proper
: ABA olrgomerx C
‘ IB '
. . A oligomers C
3.
ABA oligomers C
I

4. Melting trends and

H1 Shier

 

 

Ute 311d meCTT

l. \e t‘ '
.l.l-.rng point trcnc

1
:. P l
Comer slmcturc ..
K

3. '
Molllplfi thermal tr

' Ulrpm‘ :

EXPERIMENTAL

I. G“ “~....°u
ttlefal deiiillg
' Them ch
New.
3 “Km

2. Morphology of saturated polymers .................................................................... 154

 

 

3. Thermal behavior of the saturated polymers ...................................................... 158
4. Spectroscopic characterization ........................................................................... 166
5. XRD results for saturated polymers ................................................................... 168
DISCUSSION 171
1. Synthesis and purification ..................................................................................... 171
1. Synthesis of exact length ethylene glycols ........................................................ 171
2. Monomer purification ........................................................................................ 173
3. Polarity changes of the compounds in this research .......................................... 174
4. Polymerization details ........................................................................................ 179
H. Structure and properties of triblock oligomers ...................................................... 183
1. ABA oligomers C,,EO,Cx with y S 6 ................................................................. 183

2. ABA oligomers C,,EO,Cx with y = 7 ................................................................. 184
3. ABA oligomers CXEOny with y > 7 ................................................................. 195
4. Melting trends and odd-even effects in triblock oligomers ............................... 199
III. Structure and properties of (AB)n microblock copolymers ................................... 205
1. Melting point trend compared to the triblock oligomers ................................... 205

2. Polymer structure controls ................................................................................. 207

3. Multiple thermal transitions of the polymers ..................................................... 213
IV. Comparison to other structurally similar (AB)n copolymers ................................. 214
EXPERIMENTAL 217
I. General details ....................................................................................................... 217
1. Thermal characterization of model compounds and polymers .......................... 218

2. Solvents .............................................................................................................. 219

viii

3. .1:an ..............
t. Sodium mirrors
5. Celtic and 1hr .11:
1 Synthesis of them.

1, Stnthexrs of ethj-

 

l Etl'.)lene glwftl -‘
Eur: length eth}
1. llrdeleompmnti
5, General pttxetluz;
6. SC'IICICKS molyh:
7. General procedur.
3. General proccddr

I hurl-her of comp-.1117

hour ....,,,

“M...I

humour .......

 

3. Argon ................................................................................................................. 220

4. Sodium mirrors .................................................................................................. 220
5. Celite and alumina packed funnel for monomer purification ............................ 221
11. Synthesis of chemicals in this project ................................................................... 221
1. Synthesis of ethylene glycol oligomer ditosylates ............................................. 221
2. Ethylene glycol oligomer monotritylates and ditritylates .................................. 223
3. Exact length ethylene glycol oligomers ............................................................. 226
4. Model compound syntheses ............................................................................... 228
5. General procedure for monomer syntheses and purification ............................. 236
6. Schrock’s molybdenum catalyst ........................................................................ 242

7. General procedure for the synthesis of ethylene oxide-segmented polymers... 243

 

8. General procedure for preparation of saturated polymers ................................. 249

111. Number of compounds .......................................................................................... 251
APPENDIX -- - - - -------- -- - - - ..... - - - 252
BIBLIOGRAPHY ------- - - -- -- - - - -------------- - - e277

 

ix

 

ligunl. llorphologrc~
Tami Schemetre pr...
Farrel. Slorpholog} r.

Tml PEO cr)’\t;rll;/;

 

Terri. Structures of p
5:11.16. Solid state strut
Tm 7. Conformation 1

Ethel. Structures of .1

Tenet Solid state p...

Flinn 10. Monomer put

.
c
0..

LIST OF FIGURES

Figure 1. Morphologies of block copolymers ................................................................... 5
Figure 2. Schemetic phase diagram of a typical block copolymer .................................... 5
Figure 3. Morphology model of thermoplastic rubber ...................................................... 9
Figure 4. PEO crystallized with integer chain folding at different temperature ............. 16
Figure 5. Structures of polyethylene oxide and linear polyethylene ............................... 52
Figure 6. Solid state structure of surfactants CxEOy ....................................................... 58
Figure 7. Conformation of triblock oligomer CloEssz ............................................... 62
Figure 8. Structures of diblock oligomers F,,,Hm .............................................................. 62
Figure 9. Solid state packing of polymer (CHZCHZCFZCF3)n ......................................... 67
Figure 10. Monomer purification set-up ......................................................................... 75
Figure 11. DSC heating and cooling scans of triblock oligomer C14EO3C14 .................. 82
Figure 12. DSC heating scans of triblock oligomers CoEOyCG ....................................... 83
Figure 13. DSC heating scans of triblock oligomers CgEOng ....................................... 84
Figure 14. DSC heating scans of triblock oligomers CmEOYCm .................................... 85
Figure 15. DSC heating scans of triblock oligomers CnEOnd .................................... 86
Figure 16. DSC heating scans of triblock oligomers C14EO,C14 .................................... 87
Figure 17. DSC heating scans of triblock oligomers CmEOyCm .................................... 88
Figure 18. Types of DSC endotherrn peaks seen for triblock oligomers ......................... 89
Figure 19. Melting point and heat of fusion measured by DSC ....................................... 89
Figure 20. DSC heating scans of triblock oligomers CxE07C, ...................................... 94

Figure 21. DSC heating scans of triblock oligomers C14EO7C14 annealed at 35 °C for
the indicated time ........................................................................................................ 95

Mull, DSC he Jim:
.‘ “ferent solutions. ..

rm 3. Lou angle .\
Terrell. Wide angle .\
Tennis. Lon angle p
figure 36. Wide angle
Tgmll. Lon angle p
113mm Wide angie {-
Fm”. low angle pm

Time? Widt’ LITEZIC p.

..................

 

111m ‘1 L0“ £111 git pm
Cool obtained h} 2‘.

4: :mndb OT (11716 in

Ferret: Wldcan 1.

t5: obtained ht r1,

-
'-
I.
......

-__
c
.....

Figure 22. DSC heating scans of triblock oligomers C14EO7C14 crystallized from

different solutions. ...................................................................................................... 96
Figure 23. Low angle XRD for C16EO3C16 .................................................................... 98
Figure 24. Wide angle XRD for C16E03C16 ................................................................... 99
Figure 25. Low angle powder XRD of triblock oligomers CMEOyCu ........................ 100
Figure 26. Wide angle powder XRD of triblock oligomers C14EOyC14 ....................... 101
Figure 27. Low angle powder XRD of triblock oligomers C,‘EOI..Cx ......................... 102
Figure 28. Wide angle powder XRD of triblock oligomers CxEOMC,‘ ........................ 103

Figure 29. Low angle powder XRD of C14EO7C14 crystallized by different methods. 108

Figure 30. Wide angle powder XRD of C14EO7C14 crystallized by different
methods... ... ............................................................................................................. 109

Figure 31. Low angle powder XRD of C14EO7C14 crystallized by different methods.
Crystal obtained by flash quenching from melt, then holding at room temperature for
the periods of time as indicated. ............................................................................... 110

Figure 32. Wide angle powder XRD of C14EO7C14 crystallized by different methods.
Crystal obtained by flash quenching from melt, then holding at room temperature for
the periods of time as indicated. ............................................................................... 111

Figure 33. Low angle powder XRD of C14EO7C14 crystals obtained by isothermal
crystallization at 41.5 °C. ......................................................................................... 112

Figure 34. Wide angle powder XRD of C14EO7C14 crystals obtained by isothermal
crystallization at 41.5 °C. Bottom: crystal tested right after obtained, Top: crystal

stored at room temperature for two months .............................................................. 113
Figure 35. Powder XRD evolution of C14EO7C14 annealed at 35°C. ........................... 114
Figure 36. IR spectrum of C14E03C14. ......................................................................... 117

Figure 37. IR spectra of C14EO7C14 crystallized from hexanes (bottom) and methanol
(top) solutions. .......................................................................................................... 118

Figure 38. Raman spectra of C14EO7C14 crystallized from hexanes (bottom) and
methanol (top) ........................................................................................................... 119

Figure 39. Raman spectra of C14EO7C14. Samples were obtained by quenching from the
melt, and stored at room temperature. Spectra were taken at the time intervals
indicated in the figure. .............................................................................................. 120

xi

ligrrrt 40. Runm spee'
it: melt. and stored .
tinned rn the fr gt:

Barri]. Slzerogruphx

-.. r , 1,, .
..Os~-I‘Or.lflltd righ.

Tenn 12. Slierogrrphs
Ear-311111611 light

figure 13. Slterogrnphx
:xv-polmzed light

Tun“ Slrerogrurhx

Tun 14. Slrerogruphx

23.1.1C33C3I:()|01n
gamed light.

 

Tania. MlClOETLiI‘h\ r

g. . (QICJ'ZOH 1n
m ed iight.

Rafi"- LN freq .

.Usrlk

...e.'ent methods. ..

'f-alt
“1;. n...

1'.
W948 DSC heatrn:«

-
-..
o
'-
I
‘-
'-
a
o
o
I
a.

Figure 40. Raman spectra of C14EOI4C14. Samples were obtained by quenching from
the melt, and stored at room temperature. Spectra were taken at the time intervals
indicated in the figure. .............................................................................................. 121

Figure 41. Micrographs of polymers (CangE05)n (left) and (anC9E06)n (right) under
cross-polarized light ................................................................................................. 126

Figure 42. Micrographs of polymers (CgrthEO7)n (left) and (C91CC9EO7)n (right) under
cross-polarized light ................................................................................................. 126

Figure 43. Micrographs of polymers (CarthEOg)n (left) and (CgrthEOg),, (right) under
cross-polarized light ................................................................................................. 127

Figure 46. Micrographs of polymers (C31CC3EO7)n under non-crosspolarized light. 127

Figure 44. Micrographs of polymers (C31rC3EOm).. (upper left), (C47tC4EOlo)., (upper
right), (CsrthEOm)., (lower left), and (C91tC9EOm),| (lower right) under cross-
polarized light. .......................................................................................................... 128

Figure 45. Micrographs of polymers (C31tC3EOl4).. (upper left), (C41tC4EOl4),, (upper
right), (C31CC8E014)n (lower left), and (C91CC9E014)n (lower right) under cross-
polarized light. .......................................................................................................... 129

Figure 47. Low frequency region IR for polymer (CgTCC9EO7)n crystallized using
different methods. ..................................................................................................... 131

Figure 48. DSC heating scans of polymer (C31tC3EOy)n after flash quenched from the
melt. .......................................................................................................................... 135

Figure 49. DSC heating scans of polymer (C41rC4EOy),, after flash quenched from the
melt. .......................................................................................................................... 136

Figure 50. DSC heating scans of polymer (CarthEoy)n after flash quenched from the
melt. .......................................................................................................................... 137

Figure 51. DSC heating scans of polymer (CthCgEOy),, after flash quenched from the
melt. .......................................................................................................................... 138

Figure 52. DSC heating scans of polymer (C31tC3E06).. with different crystallization
histories ..................................................................................................................... 139

Figure 53. DSC heating scans of polymer (C31tC3EO-,)n with different crystallization
histories ..................................................................................................................... 140

Figure 54. DSC heating scans of polymer (C31CC3EOs)n with different crystallization
histories ..................................................................................................................... 141

xii

MESS. DSC heatrn g

hstenes............. ..

11:th 56. DSC heatzn g

lu'lh

figure 57. DMA and l)
are 0111 results for

Ttgnrt58. Lon angle .\

:isttlltrrtron condr'

Ttgurril. Wide angle .\.
:jtszt‘lrzzrtron eontlr'.

figure“. DSC Olpttlx'r
qtenehed from the P.
were performed .......

Tet-err. XRD or an

Tun 62. Micrographs -
ranted light.

511111113. Micrographs r.
iftetent band it idth

. '\

F .
{In 61 Micrographs r
l r 0n).tlonerleft

 

 

 

I.
'-
u..
u
""""
In
UI.
.-
.,

 

Figure 55. DSC heating scans of polymer (C31tC3EOm)In with different crystallization
histories ..................................................................................................................... 142

Figure 56. DSC heating scans of polymer (C31IC3EOI4),, with different crystallization
histories. .................................................................................................................... 143

Figure 57. DMA and DSC of polymer (C..1rC..EO3)n heating scans. The bottom 3 traces
are DMA results for the a sample in a parallel plate geometry. ............................... 146

Figure 58. Low angle XRD of polymer (C97EC9EO7)n samples prepared using different
crystallization conditions. ......................................................................................... 149

Figure 59. Wide angle XRD of polymer (anCgEO7).. samples prepared using different
crystallization conditions. ......................................................................................... 150

Figure 60. DSC of polymer (C41tC4EOs).. heating and cooling at 10 °C/min after flash
quenched from the melt. Arrows indicate the temperatures where XRD experiments
were performed. ........................................................................................................ 151

Figure 61. XRD of polymer (C41tC4EOs)n as a function of temperature. ..................... 152

Figure 62. Micrographs of polymers (CmEOtg)u (left) and (CmEO-l)n (right) under cross-
polarized light. .......................................................................................................... 156

Figure 63. Micrographs of polymers (CmEO7)n under cross-polarized light showing
different band widths. ............................................................................................... 156

Figure 64. Micrographs of polymers (C10E03)n (upper left), (CmEOm)n (upper right),
(CloEOl4).. (lower left), and (C20E07)n (lower right) under cross-polarized light. . 157

Figure 65. DSC heating scans of polymers (CmEOy)n after flash quenching ............... 160

Figure 66. DSC heating scans of polymers (C10E06)n with different crystallization
histories ..................................................................................................................... 161

Figure 67. DSC heating scans of polymers (CloEO7)., with different crystallization
histories ..................................................................................................................... 162

Figure 68. DSC heating scans of polymers (C10E03)n with different crystallization
histories ..................................................................................................................... 163

Figure 69. DSC heating scans of polymers (CmEOm)n with different crystallization
histories. .................................................................................................................... 164

Figure 70. DSC heating scans of polymers (CloEOl4)., with different crystallization
histories ..................................................................................................................... 165

Figure 71. IR spectra of polymer (CzoEO-l)n crystallized with different solvents. ....... 167

xiii

Ttgurt 72. DSC 01 pol}
tuenthed from the ::I
treer normed rn ..

Trgnrr73 XRD 01 poi}

‘1"‘6 aredrttrie'.

figure 74. Esilmdlt‘d \-
Surbers in the lnxe'

 

Ttgurels. Triblock 01:;
PEG CORIOTUIJllOm

Tenth. Tnhloelt olz.‘
T1311! T7. Ramln spec's

“Will’s TT‘rDltxk 01;;
“Walton Top

 

 

Tim 79. Oligomer C r

T?
1.111680.D-s“;1t‘1n2\t"
{reticulated end In

“gang! Rmdn‘ 3 LIT
W82. “611

1 Ing ‘ v

14: HIS-H. P‘ 1r

~..
'0
......
-.
"..

Figure 72. DSC of polymer (CloEOs)n heating and cooling at 10 °C/min after flash
quenched from the melt. Arrows indicated are temperatures where XRD experiments
were performed in addition to —178 and —130 °C. ................................................... 169

Figure 73. XRD of polymer (CmEOs),. as a function of temperature. Note: peaks at
31.7° 20 are diffraction from NaCl impurity. ........................................................... 170

Figure 74. Estimated solubility parameters of unsaturated polymers (anCxEOy)n.
Numbers in the inset are x values. ............................................................................ 178

Figure 75. Triblock oligomer C16EO3C16 calculated end to end distance with different

PEO conformations ................................................................................................... 185
Figure 76. Triblock oligomer C16EO3C16 with lamellar structure. ............................... 186
Figure 77. Raman spectra comparison between C14EO7C14 and PEO. ........................ 187
Figure 78. Triblock oligomer C14EO7C14 structures obtained from solvent

crystallization. Top: from methanol. Bottom: from hexane. .................................. 188
Figure 79. Oligomer C14EO7C14 solvent crystallization mechanism ............................ 190
Figure 80. D-spacings of oligomer C14EOyC14 measured by powder XRD compared to

the calculated end—to-end distances. ......................................................................... 197
Figure 81. Raman spectra comparison between triblock oligomer and PEG. ............... 198

Figure 82. Melting points of CxEOny triblock oligomers. Numbers in the inset are x
values. ....................................................................................................................... 202

Figure 83. Bending of the triblock oligomers caused by the angle difference in C-C-C
and C-O-C ................................................................................................................. 203

Figure 84. Percent heat of fusion deviation versus numbers of ethylene oxide units for
oligomers CsEOyC3 (top) and C14EOyC14 (bottom). ............................................... 204

Figure 85. Melting points vs. numbers of ethylene oxide units of triblock oligomers and
polymers. .................................................................................................................. 206

Figure 86. Packing of unsaturated polymers (C91tC9EOy)ll with a planar zigzag PEO
conformation. ............................................................................................................ 21 1

Figure 87. Comparison of model compound C14EO7C14 and polymers (C91tC9EOy)n.211
Figure 88. Packing model of unsaturated polymers (C91tC9EOy)n in crystalline state. 212
Figure 89. DSC heating scans of triblock oligomers CxEOZCx .................................... 253

xiv

figure 90. DSC heatzi
figure 91. DSC heat:
figure 92. DSC heatzr
Ttgure 93. DSC heatrr
figure 94. DSC heatrr
figurelli DSC heatzr
[W96 DSC heatzr

113m”. DSC heatzn‘

ones

Ttgnrr 98. DSC heating

..................

est»; hem"
*t‘v'nts... 5
In
. rt 106
litre ‘ D htaIlh‘
NXT‘TneS‘. H:
Tim
. it
L 107 DS ' 0'
units 6111:.h

'-
.....
0..
0..
I...
c
c
0..

Figure 90. DSC heating scans of triblock oligomers CxEO3C, .................................... 254

Figure 91. DSC heating scans of triblock oligomers CXEO4C,‘ .................................... 255
Figure 92. DSC heating scans of triblock oligomers CxEOsCx .................................... 256
Figure 93. DSC heating scans of triblock oligomers CXE06CX .................................... 257
Figure 94. DSC heating scans of triblock oligomers CxEOgC, .................................... 258
Figure 95. DSC heating scans of triblock oligomers CxEOmCx ................................... 259
Figure 96. DSC heating scans of triblock oligomers CXEOMC,‘ ................................... 260

Figure 97. DSC heating scans of polymer (C4rtC4EOs)., with different crystallization
histories. .................................................................................................................... 261

Figure 98. DSC heating scans of polymer (C41tC4EO7)., with different crystallization
histories. .................................................................................................................... 262

Figure 99. DSC heating scans of polymer (C41IC4EOs),, with different crystallization
histories ..................................................................................................................... 263

Figure 100. DSC heating scans of polymer (C41tC4EOm)n with different crystallization
histories. .................................................................................................................... 264

Figure 101. DSC heating scans of polymer (C41tC4EOl4)., with different crystallization
histories ..................................................................................................................... 265

Figure 102. DSC heating scans of polymer (C37CC3E06)D with different crystallization
histories ..................................................................................................................... 266

Figure 103. DSC heating scans of polymer (CgrthEO7)., with different crystallization
histories ..................................................................................................................... 267

Figure 104. DSC heating scans of polymer (C3flC3EOs)n with different crystallization
histories ..................................................................................................................... 268

Figure 105. DSC heating scans of polymer (CangEOlo)., with different crystallization
histories ..................................................................................................................... 269

Figure 106. DSC heating scans of polymer (C3RC3E014).. with different crystallization
histories ..................................................................................................................... 270

Figure 107. DSC heating scans of polymer (C9KC9E05)n with different crystallization
histories ..................................................................................................................... 271

XV

Trgurt108 DSC ht‘dil.’

httones .................

Ttgutr109 DSC ht‘dllf‘.
thones .................

Tgmllo. DSC hCJIll‘.

Stones .................

Trunlll, DSC hentrn.

UEOHCS .................

Tmlll DSC hentrri.

IflJHCSH.UN.u.H.H..

 

Figure 108. DSC heating scans of polymer (C91tC9EO7)n with different crystallization
histories ..................................................................................................................... 272

Figure 109. DSC heating scans of polymer (C91CC9E08)n with different crystallization
histories ..................................................................................................................... 273

Figure 110. DSC heating scans of polymer (C91CC9E010)., with different crystallization
histories ..................................................................................................................... 274

Figure 111. DSC heating scans of polymer (C91tC9EOl4).l with different crystallization
histories ..................................................................................................................... 275

Figure 112. DSC heating scans of polymer (CzoEO7).. with different crystallization
histories ..................................................................................................................... 276

xvi

Scheme 1. Sn and art

Scheme 2. S)111i1€\1.\ oi
End-°n\311\c.\.... .

idem 3. Functional [

fist} an ate is ..........
Scheme «1. Sequentzal :

Scheme 5. Synthesis 0.
deity} methaer} is.

$911119 6. S)'111hc\l\ t)

LIST OF SCHEMES

Scheme 1. Syn and anti conformations for polymer 12 ................................................... 25

Scheme 2. Synthesis of derivatives of (it-olefin maleic anhydride alternating copolymers
and derivatives ............................................................................................................ 30

Scheme 3. Functional polymers from N -substituted poly(maleimide-alt—isopropenyl
isocyanate)s ................................................................................................................ 31

Scheme 4. Sequential anionic polymerization of styrene and isoprene ............................ 33

Scheme 5. Synthesis of poly[methyl methacrylate-b—styrene-b-butadiene-b-styrene-b—

methyl methacrylate] pentablock copolymer. ............................................................ 34
Scheme 6. Synthesis of typical telechelic polymer ........................................................... 35
Scheme 7. Synthesis of polyamideurethanes .................................................................... 37
Scheme 8. Synthesis of styrene—ethylene oxide (AB)n copolymers ................................. 37

Scheme 9. Synthesis of o—n conjugated alternating silylene-diacetylene copolymer ...... 37

Scheme 10. Ring—opening metathesis polymerization (ROMP) ....................................... 39
Scheme 11. Acyclic diene metathesis (ADMET) polymerization .................................... 39
Scheme 12. Synthesis of unsaturated polymer with perfectly alternating substituents
along the backbone ..................................................................................................... 43
Scheme 13. Generalized metathesis copolymerization scheme ........................................ 43
Scheme 14. Ring opening copolymerization of macromonomers .................................... 44

Scheme 15. ADMET copolymerization to poly[(hexamethyltrisiloxanediyl)-butenylen]46
Scheme 16. Target (AB)n microblock copolymers .......................................................... 49
Scheme 17. Synthesis of microblock copolymers containing thioethylene segments ...... 61
Scheme 18. Synthesis of triblock oligomers CH3(CH2)9(SCH2CH2)YS(CH2)9CH3 .......... 61

Scheme 19. Synthesis of triblock oligomer FnHan ......................................................... 65

xvii

Scheme 20. S}'nlht‘sl> 1. I
httnrearbon segnre

Schemell. Example»
Schernell. S}Tlll1t‘\l\ .
Schemell Synthesis .
Scheme 24. S}'lllil€\i\ ..
thflllizs S)’Tlil1t‘\l\

506111216 Synthexrm
506m}? Syntheum i
SthttntZS. Isomerrzat

 

Scheme 20. Synthesis of microblock copolymers containing fluorocarbon and

hydrocarbon segments ................................................................................................ 65
Scheme 21. Examples of acronyms for compounds ........................................................ 68
Scheme 22. Synthesis of exact length oligoethylene glycols .......................................... 70
Scheme 23. Synthesis of oligoethylene glycol ditosylates .............................................. 70
Scheme 24. Synthesis of triblock oligomers CxEOny .................................................... 74
Scheme 25. Synthesis of monomers rthEOnyrr ........................................................... 74
Scheme 26. Synthesis of unsaturated polymers (erthEOy)u ........................................ 77

Scheme 27. Synthesis of saturated polymers from unsaturated polymers (anCxEOy)u 77
Scheme 28. Isomerization of nCzEOyCzrt double bonds .............................................. 180

Scheme 29. Back-biting for polymer degradation ......................................................... 180

xviii

Table l. (Ombmdillln\

Table! Them» for p..-

:t:vnatogntphy ....
ltbltl Monomers 7:(
.r

ltbltl. Sohents Um.

1ka. Summary ot‘ tr
times C ,EO,( ,

|
Tablet Melting pornt~

WEI llerts of fnxttv

labltl dapaerngx 1:1
meats. ...............
ltbltl (1

innings tA.
Sfair-rents.

-----------------

 

LIST OF TABLES

Table l. Combinations of TrEOxH + TsEOyTs used in the synthesis of E02,.y .............. 71
Table 2. Eluents for purification of monomers (anEOnyrt) by column
chromatography .......................................................................................................... 73
Table 3. Monomers anEOnyn polymerizable by ADMET polymerization ................ 78
Table 4. Solvents used for precipitating polymers (erthEOy)... . ................................. 79
Table 5. Summary of the types of DSC endotherms observed for ABA triblock
oligomers CxEOny. ................................................................................................... 81
Table 6. Melting points (°C) of ABA triblock oligomers CxEOny. .............................. 91
Table 7. Heats of fusion (J/g) of ABA triblock oligomers CxEOyCx .............................. 92

Table 8. d-spacings (A) for triblock oligomers (C14EOyC14) with tetradecyl alkyl
segments. .................................................................................................................. 104

Table 9. d-spacings (A) for triblock oligomers (CxEOqu) with tetradecaethylene oxide
segments. .................................................................................................................. 104

Table 10. Molecular weights and PDI values of unsaturated polymers (erthEOy)n.8123

Table 11. Glass transition temperatures (°C) of the unsaturated polymers

(C,1cC,EO,)n. . . ........................................................................................................ 133
Table 12. Melting transition temperatures (°C) of polymers (anCxEO,)n. ................. 144
Table 13. Comparison of the molecular weights and polydispersities of the hydrogenated

polymers (C2,...2EOy)n and their unsaturated precursors (C,.JthEOy)n .................... 154
Table 14. Tg and Tms of saturated polymers. (°C) ......................................................... 159

Table 15. Solubility parameters 8 [(cal/cm3 )1/2] of unsaturated polymers

(c.nc.Eo,).,.... ....................................................................................................... 177

Table 16. Calculated and measured heats of fusion* for CxEOny oligomers.
(kl/mol). .. ................................................................................................................. 201

xix

L General

Bletk eoprl} rne

 

3:: :2. led to rntpn't.

(7,... .ll. '
1.31.11. 10m. in li‘tt’i‘.

‘ w

m {13131112011 from

Liferczahzation of th;

Brock copolx 111:
....::.nl} connected \e

.0 For bloek Ct‘l“

Hombrntng t1

213.:th 0 is

"u.

“~~.-‘-‘.‘atlt it '
- ' 11150 011'
L“ '

Th1; pk

meal CODCept

I
3:? :“ILP '

INTRODUCTION

1. General

Block copolymers exhibit a fascinating range of microstructures and properties,
which has led to important applications as adhesives, compatibilizers, emulsifiers, and in
their bulk form, as thermoplastic elastomers. Therefore, block copolymers continue to
draw attention from scientists and engineers more than three decades after

commercialization of this class of materials.

Block copolymers are macromolecules comprised of chemically dissimilar,
terminally connected segments. Each segment is a homopolymer chain with many repeat
units. For block copolymers with two different types of segments A and B, their
sequential arrangement can vary from AB structures containing two segments, to ABA
block copolymers with three segments, to multiblock (AB)n systems possessing many

segments.

By combining two or more chemically dissimilar segments in one molecule, one
not only obtains copolymers that combine the properties of individual segments, but more
importantly, it also gives rise to properties not found in simple polymer blends. The
basic physical concept that underlines these characteristics is phase separation. In a
polymer blend, the polymer phase separates at a macroscopic level. Domains larger than
hundreds of microns can easily be seen under microscope. Therefore, the properties of a

polymer blend is usually a simple combination the homopolymer properties. In the block

nonsense. phlxe ~
1.11108. Ph1~e see-1:.
r1 tritenres. For e t“

1

teamed with sttrent
rail} Jerend on the
1m and thermtxlt

tenet re. more 1161.11.

The mmt 0‘an
spinners. formed 1“
5:133:31: tuo phaw .
nestingres can he 1"
lift" "

e. be blocks and '
saw
canon between the '
tit; ~

.11) properties of
.r--.d[l0113 of block (1
111:3an ~ ‘

its ntth m

71
. n
l

‘3 W18 10 triblock .
b11331.
. .0813. they have

‘I
3‘.‘ .
51‘, ‘r.

“Little (1

A.

.443; J"
3 J‘ . y .
rAOtteme. 111;“?
1..
10 The Pie
2&7,» 1

“110,331 1.
did! Chitin r;

b;
' Ml’merx 1

 

copolymer case, phase separation is at the molecular level, generally on the order of the
block size. Phase separation at this level can lead to new polymer morphologies and thus

new properties. For example, both thermoplastic elastomers and toughened rubbers can

be realized with styrene-butadiene block copolymers.1 The properties of these materials
crucially depend on their morphology, both in the molten and solid state. Their phase
behavior and thermodynamics are particularly important to understand. They will be

discussed in more detail in the following section.

The most commonly encountered block copolymers are amorphous AB diblock
copolymers, formed by joining two homopolymers at a single point. The interface
between the two phases is defined by the link between the A and B blocks, and different
morphologies can be obtained by varying the magnitude of the chemical interactions
between the blocks and the ratio of the lengths of the two blocks. Since there is only one
connection between the two blocks, this kind of block copolymer is the simplest to study
and many properties of AB block copolymers have been elucidated to date. Many
applications of block copolymers, for example thermoplastic elastomers, require more
than two blocks with more connecting sites (this topic will be discussed in detail later).
This leads to triblock and even multiblock copolymers. Compared to diblock
copolymers, they have more than one chemical linking point making it possible to
effectively couple the behaviors of different phase separated domains, and expand the

range of properties available from block copolymers.

Due to the presence of a greater number of physical junction sites per
macromolecular chain, the polymer segment length in (AB)n polymers can be shorter

than in ABA polymers to achieve the same properties, which could be an important

feature for processing
edged 1n the (AB ’n a
15 ot ABA systems.
1:13:11an materr
re 1.4.13.1, microhlut
e‘:.-:.~.‘:er:z.1zton of 1A
;ti}et_‘:j~’;ene oxide .T‘

.‘3... ellyl segment et

11 Block cupoly n

L Phase sePat‘atl

When two pg].

3;.jCL. -
”.436 551732110 T

fine: ., _
3 “hinge for mu:

10mg“,

’11:

PUTTING“ hill'e

his, The
34‘. i re
IOre. a S

11%.;
.m‘i-‘Etnt
10 pr0dUCe a ‘

r- ‘ 1

true»
ltlfr PT
age 36 .
’ «flat;

fill

“Cir, ;
01’ 6‘1“]
“Est 11.
“Demo .

' II
S In 1A

“in.

“we

feature for processing. Since the size of the phase-separated domains can be greatly
reduced in the (AB)n system, it is easier to obtain a more ‘homogeneous’ material than in
AB or ABA systems. Because the size of the micro—domain can be reduced, it is more
likely that such materials have high optical clarity. The polymers studied in this research
are (AB)n microblock copolymers. In particular, we studied the synthesis and
characterization of (AB)n copolymers where the B blocks are exact length segments of
polyethylene oxide (PEO) and the A block is an exact length linear alkyl segment or a

linear alkyl segment containing a single double bond.

II. Block copolymer properties
1. Phase separation and morphology

When two polymeric materials are mixed, the great majority are highly unmixable
and phase separate. This is a direct consequence of the well-known relationship for free

energy change for mixing (AGmix) given by equation 1:

AGM=AH.—TAS. eq.1

MIX "11X

Polymers have a very small entropy of mixing (ASm) due to their high molecular
weight. Therefore, a slightly positive enthalpy (AI-1m) due to endothermic mixing is
sufficient to produce a positive free energy change, thus resulting in incompatibility (i.e.,
polymer phase separation). This incompatibility of the blend components provides a
driving force for each to aggregate in separate phases. These two-phase systems are

coarse dispersions in which the particles are usually large enough to make the blends

opaque.

Iftu‘o polymer
:eirt‘ion may be 1m
wee but the dot:
birth. In addition. th.
ties. The relattonxl.
1; A}; .. . ,. ‘
bulb. system is \
3311.115 is the degret

...gg.n\pamtneter1 re:

|
TheFlorr} Hug;
1:th on

there N, is the I'
T4“?- . '
..t;...en. B. 1 18 a dirt

'53 it blocks

.\ . .
lrcropnztxe-xepa

 

.xi-u'
ere-ti: p01 Til

tithe .
tiltm.
dB~mamx are It)

. 4‘

$33172 i111
anged in a h

If two polymeric species are coupled by a chemical link, macroscopic phase
separation may be inhibited. As shown in Figure 1,23 the A and B segments still
segregate, but the domains have dimensions corresponding to the size of the single
blocks. In addition, the domains have a uniform size, and can form ordered mesoscopic
lattices. The relationship of morphology to the relative composition of the A block in a
AB diblock system is shown in Figure 2.2 In the figure, (DA is the volume fraction of A

block, NAB is the degree of polymerization of the diblock copolymer and Z is the Florry-

Huggins parameter4 reflecting the interaction properties of the two blocks.
The Florry Huggins parameter zis defined as
1=AHm/kTNAvB eq. 2

where NA is the number of repeat units in segment A and vB is the volume fraction
of segment B. Z is a dimensionless parameter and it reflects the interaction properties of

the two blocks.

Microphase-separation leads to different classes of structures that depend on the
block copolymer composition. For very small In, i.e. NA « N); (where NA and N3 are the
number of monomer units in the A and B components respectively), spherical inclusions
of A in a B-matrix are formed, and they set up a body-centered cubic lattice (Figure 1a).
For larger values of NA, (but still N. < N3,) the A-domains have a cylindrical shape and
they are arranged in a hexagonal lattice (Figure 1b). Layered lattices (Figure 1d) form
under essentially symmetrical conditions, i.e. NA zNB. Then, for NA > N3, the phases are

inverted and the A-blocks now constitute the continuous matrix.

 

Figure l. Morphologies of AB block copolymers. White portions represent

 

block A, while dark portions represent block B of the AB polymer.

 

      

 

   

 

 

  
   
   

 

40 i i 3 I i z
= ‘L’ E E E 5 e 5
5-8 55 bicontinuous 5 5g;
30 Hspheres :é ‘5/ \g g spheres
' 0 t . : o '
m E E a E i
2 20 -- E i a s a
= 5 2 a a
10 -
homogeneous
0
0 0.2 0.4 0.6 0.8 1
(11A

Figure 2. Schematic phase diagram of a typical block copolymer

 

In addition 11‘
caries occur unle'
mole. presented
settles-6 Hexagon
snare known as a
:11: in a narrow rain.
tetreucal CZtiCUidllUll‘
if M: Segregation l"

The structures d

inner. most triblock

 

3‘0} ' .‘
,ae behatror. For in\

v I
‘frn *
I . n.-,,
I‘. \ I"
" I l
1

.tlhiliei. l. hei) I

.111. ranges. from 0. ‘

lb
T1611 more hit)-

i,
ink!” r_ . " '.

H’MHOI is EX?“
36:13.14

‘ [cpl-11160 a
1.73%.

3-1”
mtlpine

or
‘1
l“

In addition to lattices composed of spheres, cylinders and layers, periodic
structures occur under special conditions, where both phases are continuous. One

example, presented in Figure 10, is an ordered bicontinuous double diamond
structures,6 Hexagonally perforated layers (HPL)7'9 and a second bicontinuous cubic

structure known as a Ia-3-d/gyroid7,10,11 were recently found. These microstructures
exist in a narrow range of NW3, between the cylindrical and lamellar phases, and

theoretical calculations show that they are not stable relative to lamellae and cylinders in
the strong segregation limit. 12

The structures discussed above are mainly derived from AB diblock copolymers.
However, most triblock or multiblock copolymers also phase separate and exhibit similar

phase behavior. For instance, the triblock copolymer poly(2-vinylpyridine-b-styrene-b-2-

vinylpyridine), 1, has an alternating lamellar structure when the polystyrene volume

fraction ranges from 0.28 to 0.58.13

 

O Q”

When more blocks are restrained in the same polymer chain, more complicated

phase behavior is expected and new morphologies are discovered. Matsushita and co-

WOrkersl4 reported a tricontinuous double-diamond structure formed from styrene-

iSOPI'ene-Z-vinylpyridine triblock copolymer 2. A knitting pattern in polystyrene-b-

grifuethflene-m-hut}
beadler’s research ;
coibeteneb-meth ) l
sierriar weights or
afrpbologieslb At
31813018}?de 1n .

FR,“
“Mm.
D

\

, Cit on;

 

poly(ethylene-co-butylene)-b-poly(methylmethacrylate) triblock copolymers 3 was found
by Stadler’s research group. 15 The morphology of well-defined poly(styrene-b-ethylene-
co-l-butene-b-methyl methacrylate) (P(S-b-EB-b-MMA)) triblock copolymers 4 of
molecular weights of approximately 2 x 105 has been shown to have new ordered
morphologies.16 At a low EB content (6 wt%), the triblock copolymer shows PS

cylinders dispersed in a PMMA matrix. The cylinders are covered with small isolated EB

rings.

 

CHa
CHg-CHz-CHz-CHzi—QCHz—CH CHz—C'B
(I: 1-X a | b
. ”2 coocn-b

CH3
3

l
+crtz-CH—LTBcsz—csz—cHz—CHfijGHQ—ctfifl—Jfottz—c——}c

1-
O 9”? X b coocn-t;
CH3

The morphologies of microblock (AB)n copolymers where n is large are much

less frequently reported, however, phase separation does occur in many cases”,18
Since the block lengths for this kind of polymers are much smaller and the repeating

number n is much larger, the polymers show more complexity and their study requires

313:: powerful cquxpz:
Z113 11:13.14) u
tchate alternating L;

admin-{161d print;

 

unnatural dime:
mirth copolymc
tsp-:ljcncrs Wllh the s-

really mixed) 17.

t

:a. A-

:zcynamic incnn.

1.”

yawn le» fawn"

5+

. ,1.
.épgsmcr molct;
Et

{6ng more mm“...

$331 shown in Figu

 

more powerful equipment. Styrene(S)-isoprene(I) multiblock copolymers 5 of the (Sny)n

type (n = 1, 2, 3, 4) with total polystyrene volume fractions of about 0.5 were also found

to have alternating lamellar structures.19 Theoretical models based on confined-chain
and mean-field principles were used to elucidate the fundamental relationships between

microstructural dimensions and molecular characteristics in microphase-separated

multiblock copolymers in the strong-segregation limit.20 For (AB)n multiblock
copolymers with the same molecular weight, an increase in It increases the homogeneous
(residually mixed) interphase volume fraction, thereby decreasing the extent of
thermodynamic incompatibility between the A and B blocks and making microphase
separation less favorable. If, on the other hand, the block lengths are held constant and
the copolymer molecular weight is allowed to vary with n, microphase separation
becomes more energetically favored as n is increased, which is consistent with the phase

diagram shown in Figure 2.

 

 

 

 

nflm3

polystyrene

polystyrene

/

polybutadiene

 

polystyrene

polystyrene

Figure 3. Morphology model of thermoplastic rubber

Phase serum:
We’ve: The mmt 1
bcfcre. stfrenebutul
ripened rubbers. P
Lt the T, for p111,
golfstfrene is a hard .
11:1:1ttznfigure 331 3
3310mm. The n.
in: 35 thbblt‘al Clot
LL an ordinary mN-I

,‘tment. these crux

' l

331;

1 .e at temper-amt;
Wilma] 15 therefore tel

41' '
ELK?“ "
.u topolymers Lu;

,l" ..
11511" 1. ‘
X-tbifkh IS Chle

More advaneeu

5.
.gLI‘TA
1 4 ‘~

d' For exatnple

U9

B'A. ‘
‘eKZ
mg forces such

tau, -
"lb The resulting

ea

513 ct:
~11 ”“Cmmeters -

52}: -,
d‘mnxtrated [h-
C

.'*
‘1‘

v
M?
l

413011].

Shdped Slip:

 

Phase separation can be used to generate useful materials with designed
properties. The most common application is as thermoplastic elastomers. As mentioned
before, styrene/butadiene copolymers can form both thermoplastic elastomers and
toughened rubbers. Polystyrene has a glass transition temperature, Tg, of about 110 °C
while the Tg for polybutadiene is about -100 °C. Therefore, at room temperature,

polystyrene is a hard glassy block while the polybutadiene is a soft rubbery block. As

shown in Figure 321 for a PS-PB-PS triblock system, the blocks phase separate and form
two domains. The morphological domains formed by association of the hard blocks
serve as physical cross-linking and reinforcement sites, and the bulk material behaves
like an ordinary rubber. In contrast to ordinary rubber where the cross-links are
permanent, these cross-linking sites are thermally reversible, i.e. melt processing is
possible at temperatures above the T8 or Tm (melting point) of the hard block, and the
material is therefore termed a thermoplastic elastomer. It is not hard to see that AB
diblock copolymers are incapable of producing network structures, since only one end of

the soft block is chemically linked to a hard segment domain.

More advanced structural designs based on phase separation have also been
reported. For example, spontaneously organizing systems can be tailored by balancing
organizing forces such as chemical incompatibility with others such as conformational
entropy. The resulting materials spontaneously organize on length scales ranging from a
few nanometers in LC phases to hundreds of nanometers in phase-separated structures,
and even micrometers in length for surface-segregated materials. Stupp and coworkers

have demonstrated the best example of this kind of manipulation in their design of a

mushroom-shaped supramolecule.22 The triblock polymer 6 used for this assembly

10

23.11.11.101” styrene. iv
.2...» spontaneoi.
epsiion of the {w
semi roles in ih.
smut packing
tubing upper and
3351361). The \U;

HT‘EQiCCUiM CILN'.‘

 

 

 

consists of styrene, isoprene, and a rod-like block based on rigid aromatic rings. In these
materials, spontaneous noncentrosymetric organization was reported. Both microphase
separation of the two coil blocks and the crystallization of the rod component played
important roles in the selection of the unusual shape of the aggregate. This leads to
asymmetric packing of the units, which form micrometer-sized plate-like objects
exhibiting upper and lower surfaces that have hydrophobic and hydrophilic character,

respectively. The supramolecule assembly can also be chemically cross-linked to form

macromolecular clusters.23

11

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ECUICS1 ant

2. Crystallization of polymers

Like many small molecules, some polymers can be crystallized. However,
because of the dispersion in molecular weight and chain entanglements, polymer crystals
are different from small molecules. When polymers are cooled from their melts, they
produce structures which are only partially crystalline. Layer-like crystallites are
separated by disordered regions which leads to another kind of two-phase system—a
mixture of crystalline and amorphous phases. Transmission electron microscopic studies

of ultra-thin slices of polyethylene (PE) crystals show that the lamellar crystalline phase

coexists with the amorphous phase.24 Polymer crystallization requires that the
entanglements in the melt be resolved, which is unlikely to be completed within the given
time. Therefore, crystallization is preceded by demixing, whereby chain sequences which
can be stretched and incorporated into a growing crystal are separated from chains near
entanglements, which can only be excluded and shifted into the amorphous regions. The
non-crystallizable chain parts of a polymer are not only entanglements, but also include
endgroups, chemical perturbations like short chain branches, or specific local
conformations which oppose transformation into a uniform chain. They all become
accumulated in the amorphous parts of a partially crystalline polymer. Compared to
small molecules, another major difference of polymer crystals is that they rarely consist
of extended chains of whole polymer molecules. Because it is hard to achieve ordering

over a very long range, the polymer chains in polymer crystals often are folded.

Polymers usually crystallize as spherical crystals, or spherulites. Spherulites are

formed by nucleation followed by even radial growth.25 The polymer chains inside the

spherulites orient perpendicular to the radius vector in most polymers. Vaughan and

13

51.13136 showed th.
weenie of layers.
t...‘1e spherical grm

l

eterhztes exhibit a

In many can
lief. re called bani
aimed optical mi.
31:31:31 to the Mal
pikeififdeue oxrde
tieriiites. The re

55-23.“; leaf-:th seal

11 r... .
uixrslen and inn 1

Jam It . a
a: 'l‘ .
or} of the t
mhli": -
5121165311 3
2:,

Bassett:26 showed that the center of the crystal spherulite is sheaf-like and formed by an
aggregate of layers. On further growth, they become curved, and finally establish a
stable spherical growth surface. When examined using polarized optical microscopy,

spherulites exhibit a characteristic Maltese cross pattern of light extinction.

In many cases, spherulites with constantly spaced concentric rings are observed.
They are called banded spherulites. For example, a polyethylene crystal observed with a

polarized optical microscope shows light extinctions along circles in a periodic manner in
addition to the Maltese cross.26 Other polymers such as poly(8-caprolactone),27 and

polyethylene oxide28 (PEO) crystallized under certain conditions, also show banded
spherulites. The reason for this behavior is that the crystallites periodically twist on a
certain length scale. The mechanism leading to this special texture is still under

discussion and has not yet been clarified.

As small molecule system states are mainly governed by thermodynamic
equilibrium, it is important to note that structure formation for polymers crystallizing
from the melt are governed more by kinetic criteria rather than by equilibrium
thermodynamics. The structure which develops at a given temperature is that with the
maximum growth rate rather than the structure with the lowest free energy because of the
limited mobility of the polymer chains. Being kinetically controlled, structures of

partially crystalline samples are always strongly affected by thermal processing and show
a memory of the thermal history, i.e. the temperatures and times of crystallization,29130

cooling rates,31132 etc. Figure 4 shows a nice illustration of PEO (Mn = 6000) crystal

growth from a melt. The rate of crystal growth, as indicated by the radius of spherulite

l4

increment over time

 

verse in growth rat

 

121.211.13.41. of the 1

expressed with empir
ii = A 0 expi _—
I

1there A and
5:... temperature.
mitigation rate. S
fill} extended Chaim

1.65615 shown in the

- elt ~
”‘3 POmt

51ibie
CXlend
Cd
Ch;

Wile»

.tilll‘llly lead\ I

increment over time, is plotted against the crystallization temperature. The expected
increase in growth rate with super cooling is seen over the entire temperature range. The

relationship of the spherulite growth rate to the crystallization temperature can be

expressed with empirical equations:2

BO
Tm—T

 

u=Aoexp( ) eq. 3

where A and Bo are constants for a given polymer, and Tm is the equilibrium
melting temperature. Therefore, the lower the crystallization temperature, the faster the
crystallization rate. Since the molecular weight is low, it is possible to grow crystals with
fully extended chains at a temperature close to the equilibrium melting temperature. This
case is shown in the far right region of Figure 4. A break at 59.5 °C is observed, which
is caused by a change in crystal structure. Crystals formed in this part of the curve are
comprised of once-folded chains rather than extended molecules. These crystals have a
lower melting point and a higher Gibbs free energy than the thermodynamically most
stable extended chain form. However, the crystal growth rate is higher which
preferentially leads to the formation of this once-folded form. On further cooling, the
twice-folded chain crystal is formed preferentially and so on until a relatively continuous

growth rate increment is reached.

In the continuous growth regime, the crystallite thickness dc at crystallization

temperature T is inversely proportional to the difference of crystallization temperature

and melting temperature, as indicated in equation 4,2 where B 1 and B; are constants.

Bi

 

d.(T) = T

+8 e.4
T 2 q

15

mm

939862 2.92% am @528 £20 .325 5:5 85:39.0 Own. .e 959".

AOL 939252
5 mm um mm mm 5 we t. we

 

 

 

P h h p p _ h L OF-

‘1. 1 m-

 

 

 

 

 

 

 

.0..-

 

 

 

 

 

 

 

(amfifiol

l6

Many well-d

ueEde crystallinit)‘

  
 

no: it would exr
textiles. For \il‘.
AB block eomhinuiii
been can er} \lLllllIL

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a he homopolfmierx

satires bearing- the

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mediation. one a

“A“ f- l 1
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remnant role in

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Multiple the

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Niels {DMA

). [h
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g S
@1531 1

O

Many well-defined block copolymers are partially crystalline. Being able to
include crystallinity as a design element in block copolymers is particularly attractive
since it would expand the range of properties that can be obtained from block
copolymers. For simplicity, we can think in terms of two limiting types of crystallizable
AB block combinations: copolymers with one crystallizable block, and those where both
blocks can crystallize. For copolymers where both the A and B blocks are long, each
block would be expected to phase separate and crystallize in the same crystal structure as
in the homopolymers. Copolymers where one or both blocks are short would form new
structures bearing the characteristic structure of the homopolymer for each block, or form
completely different structures. Because of the large AHfus associated with
crystallization, one also would expect that the formation of crystalline phases would
substantially perturb the copolymer microstructures compared to those typically obtained
from amorphous AB copolymers. In particular, crystallization kinetics is likely to play
an important role in defining the block copolymer morphology. A couple of examples

will be shown in the following sections.

1H. Multiple thermal transitions for polymers

When a block copolymer is characterized by a scanning thermal analysis
technique such as Differential Scanning Calorimetry (DSC) or Dynamic Mechanical
Analysis (DMA), they often show multiple transitions. For example, diblock copolymers
can show two Tg’s based on their degree of phase separation or show several melting-

crystallization transitions during a DSC heating scan. These properties can be classified

17

no he: Calci-‘l‘l

pfiimrphism.
L General phw

When the ti.

l‘i‘m ‘ " I -
remit hire \t‘a

 

 

 

beepifrnerx. For
egested copolyme
flow; frolf‘rilene 1.“
"13:: fixed to an...
resending to eat?
ten of the muterzul
[W'st'iphone is .i
if“ll-llfi'xition of the

iiiii‘l
A

fairer. iAB lr. IVP

 

=I’I'Ii. 1 1
~ 11nd minim l

1'31”.
C'lll

into three categories: phase separation, lamellar thickening and thinning, and

polymorphism.
1. General phase separated cases

When the two blocks of a diblock copolymer strongly phase separate on a
relatively large scale, the two polymer blocks have properties similar to the pure
homopolymers. For example, the structure-property relationship of perfectly alternating

segmented copolymers 7 based on soft poly(dimethylsiloxane) (PDMS) segments and

glassy poly(arylene ether sulphone) hard segments, have been studied.33 DMA and DSC
were used to analyze the copolymer properties. Isolated thermal transitions
corresponding to each block were observed, which is a good indication of the two-phase
nature of the material. The soft PDMS segments have Tgs near —1 15 °C while the T8 of
the polysulphone is around 150 °C. The Tg associated with the hard phase depends on
the composition of the copolymer and increases with the polysulphone block length in the
copolymer. (AB)n type multi-block polymers 8 with soft segments of polybutadiene (Mn

= 2000) and various lengths of poly(ethylene terephthalate) (PET) hard segments show

two Tgs because of the strongly incompatible blocks.34 However, as they are chemically
linked in one molecule, their Tgs are also affected by each other. The Tgs of the
polyolefin blocks in these copolymers are all higher than that of their pure homo-
oligomers indicating decreased chain mobility for the polyolefin in the copolymer, while

the Tg of the PET block is lower than that of pure PET homopolymer.

Polymers with pendent side chains that are chemically different relative to the
backbone also show multiple thermal transitions caused by phase separation. A series of

comblike semiflexible polymers 9, in which the alkyl side chains were located

18

nerfrnmetneally or
beryl. orifl. dodee}
51.2.1: melting above
for winners with l.
11. Ci’ldlIlS also sho‘

Mtg patterns.

CH.

nonsymmetrically on the ring, were synthesized by reacting hydroxypropylcellulose with

hexyl, octyl, dodecyl, and octadecyl isocyanates.35 Besides a transition for the main
chain melting above 100 °C, DSC experiments showed side-chain melting around 50 °C
for polymers with 12 and 18 carbons in the pendant groups. The sample with 18-carbon

side chains also show multiple melting transitions that correspond to different side chain

 

packing patterns.
911 <3 9+1
@E;@4%©E@r©gg@i EEOEEE-
7
fio-Bcch—(cmcmcwcwfl—olng ifocwcmoc~©4 " of}
8
O
l‘b(CH2)nHNCO
Cl'b(CHz)nHNCO:\
O OENH(CHz)nCH3
O
n = 5, 7, 11, 17

9

l9

“dill Shorter

in‘neree. Hashim

 

mae-imprene tap.
reason along the
Klein-it‘d rt‘.‘\p0n\;
o‘er-Ted both at the

=11 predictable for t3

 

 

this in the meehdni
shirtened and finally
creme Separation i1

tract-ed b} the Fox .

With shorter block lengths, the copolymer thermal transitions gradually get closer

and merge. Hashimoto and coworkers36 synthesized two series of styrene-butadiene and
styrene-isoprene tapered block copolymers and investigated the effects of compositional
variation along the main chain on microdomain structures and on linear dynamic
mechanical responses. As the segments became shorter, mixing of unlike segments
occurred both at the interphase boundary and inside the domains. The thermal behavior
was predictable for this kind of system. The two Tgs, as indicated by the loss modulus
peaks in the mechanical spectrum, gradually approached each other as the block lengths
shortened and finally coalesced. At this point, the block copolymer is a one-phase system

or phase separation is only on a very small scale. The Tg of the block copolymer can be

predicted by the Fox equation:4

3

1 Ml
__ = __ +
Ts T5"

2

eq. 5

a")

2

Where T8, and ng are the glass transition temperature of the homopolymer of the

two blocks, and M I and M 2 are the weight fractions of the two blocks.
2. Lamellae thickening and thinning

As mentioned before, PEO samples crystallized at different temperatures can give
crystals with different lamellar thickness due to chain folding. When P130 or other
crystallizable polymers are incorporated in block copolymers, they often still show multi-

melting behavior based on chain folding.

The crystallization of oxyethylene/oxybutylene (E/B) diblock copolymers 10,

with one crystallizable E block and one noncrystallizable B block, has been studied by

20

smi'aneous smal:

 

$21361. low-freqn.
l‘ltt‘b phase septum
bated on the er)‘1t;i.
cost-ire to the me.
{meme tnhloelt t

PEG. ha been stud]:

 

PEO block enrol) mt

Senstaltzanon of

 

he ransition temper

sting of the lamell

simultaneous small angle X-ray scattering (SAXS) and wide angle X-ray scattering

(WAXS), low-frequency Raman spectroscopy, and DSC.37138 It was shown that the two
blocks phase separate and the PEO block crystallizes in once to multiply folded structures
based on the crystallization conditions, while the oxybutylene block is slightly stretched
compare to the melt. The phase behavior of a low molecular weight (Mw = 6000)

symmetric triblock copolymer of poly(ethylene oxide) and poly(isobutylene), PEO-PIB-

PEO, has been studied using small-angle neutron scattering and TEM.39 This PEO-PIB-
PEO block copolymer forms an ordered lamellar phase at low temperatures induced by
the crystallization of the PEO segment in a helical conformation with a single fold. Near
the transition temperature, 45 °C, the PEO chains unfold, giving rise to significant

swelling of the lamellae.

H(OC|'|20|'l2)n(OC|"l20|‘lzC|'|20H2)mOH
10

—<CH2—CH)x——<CHz0Hz)y—

Chain folding in block copolymers does not always follow the pattern seen for

11

homopolymers. An unusual chain folding pattern for polyethylene has been reported in

diblock copolymers of poly(vinyl cyclohexane-b-polyethylene) 11.40 The orientation of
the chain—folded PE stems was parallel to the lamellar interfaces, unlike the chain folding

which has been observed in semicrystalline homopolymers and proposed for

21

erccnstalltne dll‘
gemlrcular to the
to'ie influence of 1

5.3111} morphom 1.;

l Polymorphis

 

In many e112!
teetering. lnxtead.

he miner crystal 1

rt L- h
3- x...'.\ ml"

POlwrethdnc.

[ls-.3.“ j .4
& knh mn\l U‘C‘d

r' -
kmfl-‘IW
\ :4 Mn‘ demnd

~-..l t
“than .

“Mon in the T (

Di}.
“‘“DY 0f the d
C L'f:

J'E‘w ‘
.tluOUSlV b\' r
f . dn nL
33235
v“ e

semicrystalline diblock copolymers where the crystallized chains align roughly
perpendicular to the lamellar interfaces. The unusual chain folding observed is attributed
to the influence of topological constraints on the PE blocks which crystallize within the

glassy amorphous lamellar microdomains.
3. Polymorphism

In many cases, multiple thermal transitions are not the result of simple lamellar
thickening. Instead, several kinds of crystal forms can exist in one polymer sample, i.e.
the polymer crystals exhibit polymorphism. Here we show several examples of this kind

of behavior.

Polyurethanes are a large family of very important materials that are probably the

oldest and most used block copolymers.21 Several transitions can be observed in a DSC
thermogram, depending on the nature of the solid-state structure of the sample. These
include the Tgs and endothermic meltings of crystalline and paracrystalline domains. The

variation in the Tg of the soft matrix in segmented polyurethanes can be used as an

indicator of the degree of microphase separation“,42 The endotherms associated with

the disordering process of the urethane domains depend strongly upon thermal history.

Seymour et al.43144 demonstrated that these endotherms correspond to domains of
limited short-range order (with lower melting points), long-range domains and
microcrystallites of the hard segments. Short-range ordering can be improved
continuously by annealing as evidenced by a consistent upward temperature shift of the

endotherm until it merges with the highest endotherrn.

22

l
B'Olh llle Pl ‘

melting H-bontltr.
122m mangeme:

its: less favored.

ll; ililtllilt'lll l
tel: or different L.

time. it hie-an e x
- ¥

\

‘
got
‘1

metre of the con:

L$~3fi§ofi
‘nubl by

1 Vinyl aleoh

 

H rates.~13

memlimers. polx .

Cit-Elfin

rate haie t

Ciitpi‘llirttlS. For 1

0‘1???

aid for copolx r

H W '
spectn'elx t it

leached from the

themed for these i

. tontmuOUS }
Chit“
. .t.€lSuh1Ch l1

Both the polyamides and polyurethanes are similar in that they can form crystals
involving H-bonding. One can think of different kinds of H-bonding arrangements, with
a planar arrangement being the most stable, and out of plane intermolecular H-bonding
being less favored. Distinct thermal transitions due to different H-bonding arrangements

can also be seen.

In addition to size-related polymorphs, polymers that crystallize in different unit
cells or different chain conformations also cause multiple thermal transitions. For
example, wide-angle X—ray diffraction (WAXS) measurements were used to study the
influence of the composition and thermal history on the type of lattice developed in three

different vinyl alcohol-ethylene, VAE, copolymers crystallized from the melt at various

cooling rates.45 The results were compared with those of the corresponding
homopolymers, poly(vinyl alcohol) and low-density polyethylene. Both composition and
cooling rate have been found to determine the crystalline structure of these VAE
copolymers. For samples slowly crystallized from the melt, a monoclinic lattice is
obtained for copolymers VAE7l and VAE68 (with compositions of 71 and 68 mol %
VA, respectively) while orthorhombic lattices were found for the same samples when
quenched from the melt. One unusual structure conversion phenomenon was also
observed for these polymers. As monitored by WAXS, the crystal with orthorhombic
unit cell was continuously converted to the crystal with monoclinic unit cell as indicated
by the continuous change of the lattice angle ,8. The polymorphism exhibited by these
copolymers which is unusual. Moreover, it seems that there are no differences in the

melting temperatures between the two crystalline modifications.

23

Pol y hex am.
conjugated and non.
of iti1 pohrner rexe
llamtmp 151 3C
mm. In all thre

ta minimizes It—r'.

 

3:03p relative to the
is ir: a on conforma‘
Tie ranst'nrrnatmn t
36; 3C; Y-form to m

SUV 1"

KA‘

K‘n

nu

interaettt

with .~ -
m he phdae tranxl‘or

Poly(hexamethylene-2,2’-bithiophene-5,5’-dicarboxylate), 12, has alternating
conjugated and nonconjugated segments. X-ray fiber diffraction and DSC investigations
of this polymer reveal the existence of three polymorphs.46 Both 0t- (mp ~ 125 °C) and
B-forms (mp 151 °C) belong to the monoclinic system, while the 'y-form (mp 172 °C), is
triclinic. In all three forms the bithiophene dicarboxylate group is confined to a plane
that maximizes n—n-conjugation; however, with different orientations of the carbonyl
group relative to the sulfur atom (as shown in Scheme 1, in the a- and B-forms, S-C-C=O
is in a syn conformation (left), while in the y-form, S-C-CzO is in an anti conformation).
The transformation temperatures are as follows: or- to B-form, 130-150 °C; B- to y—form,
161 °C; y—form to mesophase, 172 °C; and mesophase to isotropic, around 185 °C. The
strong 1t—1t interaction between aromatic planes is believed to be the main driving force

of the phase transformations.

9 9
{memo-(4 s chogln—

12

24

 

Scheme 1. Sin

nwwthJWWN\./O\

<.//\/\( \ 1;
4T 8

Scheme 1. Syn and anti conformations for polymer 12

\o
O
S
S
O
O
O
S
O
0\
syn

25

\
00
E2
’ o
E
o
s
s
/0

anti

   
   
  

IV. Sinthesis 01

Synthesis e‘.

111's. While the sf.

CCPJ.}THCI\. Sumn 1

3.1mm that are re;

 

1. Chain polyn

Consider a L

4%,}. . it» 2
Mt initiation. th=

Why» 0‘
P .

,.._.-.é..mg end an

\ 1115i. ffipre\c

IV. Synthesis of (AB)n Block Copolymers

Synthesis of block copolymers has been a challenge to polymer chemists for
years. While the synthetic methods for preparing AB block copolymers are relatively
well developed, there are fewer synthetic routes that yield well-defined (AB)n block
copolymers. Summarized below are some of the methods used in the synthesis of (AB)n

polymers that are related to this project.

1. Chain polymerization

Consider a chain polymerization with two kinds of monomers, M. and M2.47
After initiation, there are two types of propagating species—one with M1 at the
propagating end and the other with M2. These can be represented by M1‘ and M; where
the asterisk represents a radical, a carbocation, or a carbanion as the propagating species
depending on the particular case. Assuming that the reactivity of the propagating species
is dependent only on the monomer unit at the end of the chain, four propagation reactions
are possible. Monomers M1 and M2 can each add either to a propagating chain ending in

M1 or one ending in M2 as follows,

M,‘+M,—£u—+M,‘ eq.6
M;+M2——"n—>M; eq.7
M;+MI JHM: eq.8
M;+M2——"R—->M; eq.9

26

where kt; l\

heather 11;. kt; 11

and so on. Throug;L -

 

 

 

 

 

where kn is the rate constant for a propagating chain ending in M1 adding to

monomer M1, k12 is that for a propagating chain ending in M1 adding to monomer M2,

and so on. Through derivation, 47 one can obtain equation 10

 

 

r 2+
I: 21f] fle 2 eq.10
’ifr +2frf2+r2f2
where
rl =—ki eq.11
klZ
r2 =—]fa eq.12
k2]
WW
f =1_f = 1 eq. 13
' 2 [M.l+[le
and
Fl =l— dlM'] eq. 14

2szJ+dMJ

r, is the relative rate for the addition of monomer l and monomer 2 to a chain
ending in monomer 1, r2 is the relative rate for the addition of monomer 2 and monomer l
to a chain ending in monomer 2. f1 and f2 are the mole fraction of monomer l and
monomer 2 respectively, and F1 and F2 reflect the composition (mole fraction) of the two
monomers in the polymer. The case relevant to (AB)n microblock copolymers is

alternating copolymerization.

Alternating copolymers, where each block is just one monomer unit long (usually

two chain atoms), is an extreme case of a microblock copolymer. Strictly speaking, these

27

re not block polym
properties. Hovme
I.
3. long side eh
itemizng pol )‘men
11. we can obtain 1‘

winner in equrtt

i‘1~‘?\“i§mer chain.

 

 

 

Me“-
Me)

are not block polymers since the blocks are too short for them to show their characteristic
properties. However, some of these polymers have reactive side groups, to which can be
grafted long side chains that will give the polymer block-like properties. These kinds of
alternating polymers can be formed by copolymerization when r1 = r2 = 0. From equation
14, we can obtain F1 = 0.5 for this case, which means the two monomers enter into the
copolymer in equimolar amounts in a nonrandom, alternating arrangement along the

copolymer chain.

'B(CeF5)4
Me

Me Ti+\

 

13 14

The alternating copolymerization of ethene/propene using a metallocene catalyst
reported by Leclerc and coworkers is one example of these reactions. With the zirconium
metallocene catalyst 13 {[(3-MeCp)(Me2C)(Flu)]ZrMe2} (Cp = cyclopentadienyl, Flu =
fluorenyl), they obtained a highly alternating copolymer. The percentage of alternating
structures (M1M2M1 and M2M1M2) was estimated to be 81% based on 13C NMR analysis
of the triad distribution. Titanocene complexes based on an amido-fluorenyl ligand
bridged by a dimethylsilylene group, catalyst 14

[(1]l:ns—Cl3H3SiMe2NCMe3)TiMe]+[B(C6Fs)4]', was use to catalyze the synthesis of a

28

rcriectly alternate -
péhstirene structur

The WM 1‘.
:fixged by select:
mariner. R1011.
has-or 1111 Used '.
03-2111 and maleic .
hxcopoljmer \Wl’t
-. 1m hes (Schemt

3. .,.;
utlmltS. the\' CI

Alternating

aerrides uere 1H

T“ C01301\trrers h;

.21

4.511" -
5 mOdlfication

 

 

1131
he Mm“ bad

.
11ers» '

~241an
‘ C()l)‘-‘1.Vlnt"

perfectly alternating ethylene/styrene copolymers with a well-defined isotactic

polystyrene structure.48

The usual homogeneous morphology of simple alternating copolymers can be
changed by selectively grafting to functional groups purposely incorporated in the
copolymer. Radical copolymerization with 2,2'-azobisisobutyronitrile (AIBN) as
initiator was used to synthesize a series of alternating copolymers of straight-chain or-
olefins and maleic anhydride with a molecular weight of 2,500-37,000. Derivatives of

this copolymer were prepared by reaction of the anhydride residues with alcohols, water,

and amines (Scheme 2).49 Because of the amphiphilic characteristic of these copolymer

derivatives, they can be use to prepare Langmuir-Blodgett (LB) multilayers.

Alternating copolymers from isopropenyl isocyanate and N-substituted

maleimides were synthesized by AIBN initiated radical copolymerization (Scheme 3).50
The copolymers have an isocyanate group in the constitutional repeating unit which
allows modification and functionalization in a polymer reaction. The preparation of
amphiphilic copolymers having a hydrophobic backbone and a hydrophilic chain attached
to the polymer backbone at every other repeat unit were demonstrated as well as an

alternating copolymer with an NLO chromophore attached to the polymer.

29

Scheme 2. 5}

Wires and dcrhu’.

 

9H3
(Cw

4' M

I“DOC

Scheme 2. Synthesis of derivatives of a-olefln maleic anhydride alternating

copolymers and derivatives.

Cl'b(CHa)x-1CH=CHz + A
O O

O

J AIBN

CH;
(CH?>x-1

cr-b (EH3

«EH»... (CHz>)x.1H\‘<€:—?>—‘(_3L
w w n 1

HOOC COOH HOOC coon ”000 /C\N/

30

1

Scheme 3. 1"

1:73:31 isocyanate

 

 

 

Scheme 3. Functional polymers from N-substituted poly(maleimide-alt-

isopropenyl isocyanate)s

 

R
AIBN l benzene/6O QC
(l3Ha
Gee-1+
NCO n
O l O
R
R1OH l 2-butanone/DMF
(IDHS
CHz—C
I
NH n
0 0 <'3=o
R bn‘
R R‘
0141119 (CHZCH20)6CH3
C18H37 (CHZCHZO)GCH3

N= N02
CGHS CHeCHz/ . .

31

1 Ionic 11‘ mg

1.181,, arehr
r sequential r
of wane-isoprene
of surene with ser
Were Scheme 4 1.

In initiator. In illh

sxcznens cast fro

 

strictures.
Dtt‘unctitmal
175%

u: route has the a

W - '
.u monotttnetion'

erie
‘5' .a
.1311» 13} and but
il‘iijr‘g .. .
. dnlomc pm]

“Ci“ a:
- ‘-’h114ne/dieth r
-.l
Altman -
- ‘ ZallOn
- dip]
Earth-i . .
t3» 'htch is
1111‘
I. ‘ Carbg
nVI Or-
Mu.

2. Ionic living polymerization

(AB)n architectures are synthesized by ionic living polymerization techniques
through sequential monomer addition. For example, well-defined multiblock copolymers
of styrene-isoprene (ley)n (where n = 1-4) were synthesized by initiating polymerization

of styrene with sec-butyl lithium followed by the sequential addition of isoprene and

styrene (Scheme 4).19 Each block length is controlled by varying the ratio of monomer
to initiator. In this example, the polystyrene fractions are kept at 0.5 and all the film
specimens cast from toluene solutions were found to have an alternating lamellar

SII'UCIUI'CS .

Difunctional initiators can also be used to initiate sequential ionic polymerization.
This route has the advantage of requiring half the sequential monomer additions needed
with monofunctional initiators. With careful modification of the reaction conditions,
multiblock copolymers with more than two kinds of segments also can be synthesized.

For example, a series of, pentablock copolymers consisting of methyl methacrylate (M),

styrene (S) and butadiene (B), (MSBSM) were successfully synthesized51 by sequential
living anionic polymerization. Butadiene polymerization was initiated at room
temperature with the di-adduct of tert-butyllithium and m-diisopropenylbenzene in a
cyclohexane/diethyl ether mixture. Styrene was added, and on completion of the styrene
polymerization, diphenyl ethene was added to terminal styrene anion to decrease the
reactivity, which is necessary to prevent nucleophilic attack at the methyl methacrylate
(MMA) carbonyl group. The solvent was changed to a cyclohexane/T HF mixture and
MMA was polymerized at -78 °C (Scheme 5). In addition to classical phase

morphologies such as cylindrical and lamellar phases, these materials show two

32

rehclnsical morph

by 1131.

 

Teleehelie r
zipait} to react u:
ulnmiymerx. Th
itfifiaxanety of ele
flawed in q
stsae'mmetric arm
01 he amide pr

5‘3351'm 1' .
"*“numg dftrr

Ill C-ficpl

Mg redCllt'i

Scheme 4

r/

.—

n

O

 

nonclassical morphologies, i.e., catenoid-lamellar and strut phase structures as observed

by TEM.

Telechelic polymers, polymers that containing one or more end groups with the
capacity to react with other molecules, are useful for synthesizing block and other types
of copolymers. These polymers can be prepared by terminating living anionic polymers
with a variety of electrophilic reagents. As shown in Scheme 6, (o-amidopolystyrene was
synthesized in quantitative yields by the reaction of poly(styryl)lithium with
stoichiometric amounts of N,N-diisopropyl-4-(1-phenylethenyl)benzamide. Deblocking
of the amide protecting group by acid hydrolysis quantitatively provides the

corresponding aromatic carboxyl chain-end functionalized polystyrene which can be used

in coupling reactions.52

Scheme 4. Sequential anionic polymerization of styrene and isoprene

/

: see-BuLi _ 9 MB”

 

Benzene, 30 9C Ph Ph

 

A6
1
repeat step 1 and 2...
e
W 2__ WE”
n <-—
Ph ‘—‘ Ph

33

Scheme 5

styrene-hmethfl n‘

e

 

U -
Elm-kc

Scheme 5. Synthesis of poly[methyl methacrylate-b-styrene-b-butadiene-b-

styrene-b-methyl methacrylate] pentablock copolymer.

tBu tBu

    
 

cyclohexane

2 t-B L' e
+ U ' so QC, 2h

Li*e

 

(I)

CHz=CHCH=CHz
Cyclohexane/ether 25 ‘2C, 12h

U[(CH20H=CHCHZ) xteHCHayrbt(cwcwytcwcebcmwmj Li
CH

0142 3 CH2

/
25 9C, 2h O

Le -KCIDHCH'Z)n(Cl'lzCl'l=Cl‘|C|'|2)2x((l3HCH2)2y(Cl'12C|3"DEl-Li+
Ph (3H Ph

sas CH2

250
© 0 003.9,:

Li+'CCHzSBSCH2C'Li+ 1' MMA' ’78 'C_ OH(CCH2 escwc H20)...H

© 0 2. MeOH '

34

EC)

Scheme 6. Synthesis of a typical telechelic polymer

! Li+ 'CH—CHz-fCH—Csz—1
n-

C=CH2

o +

 

35

3. Step Ct

Typieai
ptrijnrzenzatior
isocyanates.
of low moleet

oezerriene elm

Starting
from: other po
ethylene oxide
ttiystjrene to
Deanediate u

SIEp-gri
d’iflwmes an

Q11". 1,.
t‘thL

111111115

1 .
“litttayborl in”;

r.
0. be L156 0f ll]
“as foilrid that

3. Step copolymerization

Typically, microblock copolymers are prepared by the step-growth
polymerization of difunctional monomers derived from carboxylic acids, such as
diisocyanates, anhydrides, diesters, and diacids with diols or diamines, often in the form

of low molecular weight oligomers. In a typical example, as shown in Scheme 7, an

oligomeric diisocyanate is reacted with a polyol to yield a polyamideurethane.53

Starting materials for blocks used in step copolymerization can be synthesized
from other polymerization methods. For example, Finaz et 01.54 prepared styrene-
ethylene oxide (AB)n copolymers by using phosgene to convert a dicarbanion-terminated
polystyrene to a diacyl chloride-terminated oligomer, followed by condensation of this

intermediate with polyethylene glycol (Scheme 8).

Step-growth polymerizations involving functional groups other than acid
derivatives are also readily available and widely used. For instance, coupling of
oganolithiums and chlorosilanes is an effective way to make copolymers that contain
hydrocarbon and silicon segments in their backbones. Shown in Scheme 9 is an example
of the use of this kind of reaction to make a o—rt conjugated altenating copolymer.SS It
was found that the 6- It conjugation was enhanced when the number of silicon atoms in

the silylene block was increased.

36

Scheme 7. Syr.

OCN—R—

+CONH—i

Scheme 8. S} :-

 

Scheme 7. Synthesis of polyamideurethanes

OCN—R—CONH—RZ—NHCO—R—NCO + HO—Fl"—OH

l

+60NH—R—CONH—Rz—NHCO—R—NHco—o—RLo);

Scheme 8. Synthesis of styrene-ethylene oxide (AB)n copolymers

Na+ 'CHCHQWCHzCH' Na+

O 0

COCI2
O 0

II II
CICCHCHQWCHZCHCCI

O O

l H(OCH2CH2)YOH
o o
II II
{cfcmHz CHzCHfix—C—QOCl-bCHzil—Oa:

O 0

Scheme 9. Synthesis of o—Ir conjugated alternating silylene-diacetylene

 

copolymer

or or CI+Si:-)—Cl
\ /

0:0 [Cl 4 n-BuLi

/ \ —>LiE-ECCCCLi “ch000}
CI C=C THF '

cr/ \Cl m=1,,,346

 

37

.1 Metathesi‘

in recent }
again in the a!
Mmenzanon pr '
ROMP» and My
mead via the s-
double bond to a n
m C=C double
bond remains cont.
{07115 the basis (‘
reversible. the int
«“3 the rates of in

first.

shmm in S Chen

35:2? a ,
“Mflobumn
c

 

r‘-‘5}mfir3. A3 n
. m

WK ~ .
.menZathns 0'”

"‘MC .
b) ‘prOd UCI

5,5.» h
1'3?
x, e - .

4. Metathesis Polymerization

In recent years metathesis polymerization has made an increasingly significant

impact in the advanced materials arenas6 There are two kinds of metathesis
polymerization processes involving alkenes, Ring Opening Metathesis Polymerization
(ROMP) and Acyclic Diene Metathesis Polymerization (ADMET). Both polymerizations
proceed via the same basic mechanism involving a 2 + 2 cycloaddition of an alkene
double bond to a metal alkylidene (or carbene) to give a metallocyclobutane intermediate.
If the C=C double bond is constrained within a ring, then the newly formed C=C double
bond remains connected to the metal alkylidene. The mechanism shown in Scheme 10
forms the basis of the ROMP reaction. ROMP can be living when the steps are
irreversible, the intermediates are stable on the time scale of the polymerization reaction,
and the rates of initiation and propagation reaction are of similar orders of magnitude,

then.

ADMET polymerization involves step-growth polymerization of dienes. As
shown in Scheme 11, the polymerization cycle involves the formation of
metallocyclobutane intermediates that lead to dimer, trimer, and eventually to high
polymers. As noted in the scheme, each step is reversible. Like many step-growth
polymerizations, obtaining high molecular weight polymer relies on the generation of a
volatile by—product, in this case ethylene, which is readily removed under vacuum to

drive the equilibrium to favor the condensation process.

38

Scheme 10. R:

 

+ i
M:C
_ I
M:
SCheme 11. Ac
\ \
+ ‘\
M:CHR
' V l,/‘\
§ ll . .
. + E
M l

Do

Scheme 10. Ring—opening metathesis polymerization (ROMP)

Q—fi—«x
+‘—__ I
M__E AA R

M=CHR R

— - Q
“WW? 51

 

 

 

 

Scheme 11. Acyclic diene metathesis (ADMET) polymerization

1(7— ‘——:_‘II+IL

+ M——
M=CHR I"'12 M R

J3 _. ”2%

—— f m 2 +

H + m
M M— —

 

 

 

 

 

 

polymer -——*~ W

 

39

The olefin
Lung it as 3 p4.
merited. This v
{timely stable
taxman: have be:

of a transition m

 

examples. Wagcnc

palmenze 1.9‘dCK

Cum POI}‘mel.

Kildfiifils catah \

01 organic functio

The olefin metathesis reaction has been known for many years,57 but progress in
using it as a polymerization technique was slow until well-defined catalysts were
invented. This was especially true for ADMET since it requires highly active yet
relatively stable and long lived catalysts. Traditionally, metathesis polymerization

reactions have been carried out in solution using dual-component formulations consisting
of a transition metal halide and a main group alkyl metal co-catalyst.58 In early
examples, Wagener and his colleagues59 employed the WCldEtAlClz catalyst system to

polymerize 1,9-decadiene and 1,5-hexadiene, and Nubel et a1. 60 used a modified catalyst
WCldEtAlClglPrOAc, to synthesize polypentenamer from 1,5-hexadiene. However, both
catalysts polymerized hydrocarbon diene monomers with limited success. Since classical
metathesis catalysts are generally strong Lewis acids, they do not tolerate a wide variety

of organic functional groups in monomers.

O

N
F3C H _ /H
ng'lM— C

mgr 3?
F30

CH3

15

Well-defined Lewis acid-free transition metal alkylidene complexes were
developed in the late 80’s and early 90’s. These catalysts have been very successful in

carrying out ROMP and ADMET polymerization of cyclic olefin and acyclic diene

4O

monomers h‘dVli
caaEpLs are n‘

cos often6 1 ‘54

mu‘oriersbs'é

The 11:
Diet? ~ .
lun aIIIn1[\

iDiffz‘

ROMP and A

0,“ e
(“-e p
. ll, ”1013]

V .

monomers having different organic functionalities. The most widely used metathesis

catalysts are molybdenum and tungsten complexes 15 developed by Schrock and
coworkers61'64 and ruthenium complexes 16 and 17 developed by Grubbs and

coworkers.65'68

P
TRa ---- Ph Cl I CY3 /H
""""""""" 'Ru=C

C'")Ru=~"" ‘Ph Cl/ l
C' I PCY3

PR3 X

(R = Ph or Cy) (X = H or Cl)

16 17

The ligands in the Schrock’s catalysts were carefully chosen to combine high
olefin affinity and low Lewis acidity, so that they selectively react with olefins and
tolerate polar functional groups. Schrock’s catalysts are very effective in initiating both
ROMP and ADMET polymerization. However, these catalysts are very sensitive to
oxygen, moisture, and some reactive functional groups, and are inconvenient to

synthesize.

In contrast, Grubbs’ ruthenium carbene metathesis catalysts65‘68 16 and 17 are
much less sensitive to oxygen and water, and they are more tolerant of organic functional

groups. In fact, reactions using these complexes as catalysts can even be carried out in

aqueous media.69 Although they are effective for both ROMP7O and ADMET

4l

miymenzatio:

Schnx‘k's cat;

Both A
u-eideszgned
can be pol yme
bitch and one
of 5.6-dl"h€fl}'l
1

Ki'h'EZ-‘llm- “I
-.-. alum I ‘

scantuents alo.

Metathe:

monomers. Wk

 

polymerization,71 their activity for ADMET polymerization is much less than for the

Schrock’s catalysts.

Both ADMET and ROMP have been used to prepare microblock copolymers. A
well-designed monomer that contains different segments and polymerizable double bonds
can be polymerized by metathesis methods to give a polymer with perfectly alternating
blocks and one double bond in each repeating unit. For example, (Scheme 12) treatment

of 5,6—diphenyl-l,5,9-decatriene, with Schrock’s tungsten catalyst, allowed Wagener and

Konzelman72 to selectively form an unsaturated polymer with perfectly alternating

substituents along the backbone.

Metathesis polymerization can also be used to generate copolymers from two
monomers. When the metathesis reactivity of the two monomers is similar, they form
random copolymers (Scheme 13). The process can be easily explained since either

monomer can add to the reactive species in the polymerization cycle, thus producing a
random copolymer. Heroguez et al.73 reported a ROMP copolymerization of two

norbomene macromonomers containing either polystyrene74 or polyethylene oxide75
units (Scheme 14). Starting with a mixture of both macromonomers, ROMP was
triggered by the addition of Schrock’s molybdenum catalyst, and after 1 h, the
polymerization was terminated with the addition of benzaldehyde. During GPC
measurements, they found that the polymer was homogeneous to both UV and refractive
index (RI) detection, which implies that the copolymer is not a block-like polymer.
When the two macromonomers were added sequentially, a block copolymer can be

obtained because of the living nature of ROMP.

42

Scheme 1.

segments along I

W

Scheme 13

Scheme 12. Synthesis of unsaturated polymer with perfectly alternating

substituents along the backbone

O [m O

- CHQCHQ
\\ \\ ‘\\ ,{”\\

Scheme 13. Generalized metathesis copolymerization scheme

Q + Q . J- ' 7:

ROMP 4n — —

 

 

/

 

 

 

 

 

 

 

 

all

HzC=CH—X—CH=CH2 + HzC=CH—Y—CH=CHQ

ADMET 1 catalyst. - CzH4

—ECH=CH—)gn—ECH=CH—Y3r—n

43

Scheme 1

a

Scheme 14. Ring opening copolymerization of macromonomers

" Q

 

 

 

Block C
ADMET cop”
buzenylene] 18
cemhmenzatit
weight?6 becaL
insoluble oligo
scheme 15,.”
tungsten catal}
solution of bit
communion, 1

milei'le and l

i L
bipienflene w

Penectly we.“

slums-5‘

Block copolymers with an (AB)n structure can be synthesized by controlled
ADMET copolymerization. For example, both poly[(hexamethyltrisiloxanediyl)-
butenylene] 18 and polybiphenylene 19 can be obtained by ADMET polymerization, but

copolymerization of the monomers does not yield a copolymer with high molecular

weight76 because of the dimerization and trimerization of the aromatic monomer to give

insoluble oligomers. The cross metathesis was achieved with a controlled experiment

(Scheme 15).77 Diallylhexamethyltrisiloxane was first oligomerized with Schrock’s
tungsten catalyst and diluted in a toluene solution. To this system, a dilute toluene
solution of biphenyldiene 20 was added over a period of 1 h. Because of its low
concentration, homopolymerization of this monomer was limited. With the evolution of
ethylene and propylene, the copolymer with alternating oligosiloxane butylene and
biphenylene was obtained. However, the block lengths are not exact, so this is not a
perfectly alternating system. The polymer structure was confirmed by NMR and TGA

studies.

00
n

19

45

Scheme ?

:ienyiene]

\\,.

J

Clix? CH3 5

f . t. I.
778K051.

Scheme 15. ADMET copolymerization to poly[(hexamethyltrisiloxanediyl)-

butenylene]

CH3 CH3 (3H:3
oral \/ CHG CHa
/\/Si\o ISi\O ,Si</\
l [W]catalyst
CH; CH; CH3
oral V 0.5% Gem I. \/ ll/CHa

Sl\ [SL‘ [Si\/\
N O O l\/\ n

18
J/“J l [W] catalyst

CHaCHa CHa Crb\ /Hac

C CH3\ I
HRSIK O,\Si/\Has O’ :Wn/Si\o ’\Si/\ (TQM?

46

5, C ompa

copol,”

Althou;
hie :d'iantage
his project 5
copiiymerizat
am block
zero is very lir
cmmi. but th=
lli Addition. te
mien of mo
5351 not be \er

ROM]

~ll .
an ICECIIOHS‘
Pill} median I;

11%th Sec
{0 HEWIE. ar
SIEp-

Cam-:1
i $771613

5. Comparison of different polymerization methods for obtaining (AB)n

copolymers

Although (AB)n block copolymers can be synthesized in many ways, each method
has advantages and disadvantages. Uniformity of segment length is a major concern in
this project since it greatly affects the crystallinity. Most conventional chain
copolymerization methods, such as radical and ionic polymerization, do not generate
uniform block lengths. Also, the number of monomer pairs with both ti and r2 equal to
zero is very limited. Living polymerization can generate monodisperse blocks with good
control, but the blocks are not of exact length and are described by a Poisson distribution.
In addition, termination and chain transfer reactions occur with the addition of each new
portion of monomers. Therefore, n, the number of repeating unit in an (AB)n copolymer

can not be very large.

ROMP is also a chain polymerization. If the monomer is designed to contain both
blocks, it can give exactly alternating microblock copolymers. However, as required by
all reactions, polymerization must result in a decrease of free energy, and in ring opening
polymerization, the ring strain determines the polymerizability of cyclic monomers. This
limits the scope of ROMP polymerizations. In addition, large cyclic olefins are difficult

to prepare, and thus most ROMP examples involve the opening of small rings.

Step-growth polymerizations are usually used to prepare most microblock
c0polymers because of easy access to the needed monomers. By carefully selecting
monomers, the resulting copolymers normally have exact block lengths. However, step-
growth polymerizations require exact stoichiometry for the polymerizations to reach high

molecular weight. Many step growth polymerizations are condensation reactions that

47

yield a small
removal of [hi
'n‘sh moleculu

condensation :

The A
mlyrnerizatio:
156 an) diene
needed for RC
enables 53.16:
Miners M15

COmp‘
EDIE 56mm“

There hate be

iepefldem 0n

yield a small molecule by-product such as water. Because of its equilibrium nature,
removal of the byproduct is crucial for driving the equilibrium to high conversions and
high molecular weights. Compared to chain-growth polymerizations, reaction times for

condensation schemes are usually long.

The ADMET scheme is a step growth process and compared to ROMP, ADMET
polymerization rates are much slower for the synthesis of the same polymer. However,
the (1,0) dienes needed for ADMET generally are easier to prepare than the cyclic olefins
needed for ROMP, allowing easy access to a wide variety of monomer structures. This
enables systematic studies of the evolution of the structures and properties of the

polymers with variations in the lengths of the individual microblocks.

Compared to traditional polymerization methods, metathesis polymerization is
more sensitive to impurities and functional groups due to the sensitivity of the catalysts.

There have been reports showing that the success of this kind of polymerization is largely

dependent on the purity of the monomer.59978,79

V. Target molecules in this research

We are interested in a set of block copolymers, (AB)n microblock copolymers,
where, the AB pattern is repeated n times and both blocks can crystallize. As shown in
Scheme 16, the polymers contain two blocks with distinctly different properties. The A
block is an exact length oligoethylene or oligoethylene that contains a single double
bond, while B block is an exact length oligoethylene oxide. Thus the A block is

hydrophobic, and the B block is hydrophilic. The amphiphilic character of these

48

Inicrobloeks r
surfactants. r

lOtllC con-duet

Scher

c, ... .
mklit'itx‘
oi the Neck

n -.

[30 L
A AlOlC)gl§

microblocks could lead to surfactant behavior and therefore have practical applications as
surfactants, polymer blend compatibilizers, and because of the polyether segments, as

ionic conductors.

Scheme 16. Target (AB)n microblock copolymers

branching or crosslinking site

{max—CH:CH—ICH2)x—(00H20H2)y03;

\

hydrophobic hydrophilic

\ /

—BCH2)2X+2—(OCH20H2)yO];

Based on the properties of the homopolymers, these copolymers are expected to
strongly phase separate and be highly crystalline. The crystalline systems that have been
studied to date have often been poorly defined in terms of the block lengths and their
connectivity. Being able to incorporate exact length segments can increase the regularity
of the block copolymer and therefore increase the crystallinity. Because of the shorter
block lengths in (AB)n copolymers, these polymers may exhibit more complicated
morphologies than simple AB block copolymers. One particularly interesting feature of
PE/PEO microblock polymers is that the PE and PEO blocks normally adopt strikingly
different crystal structures. PE crystallizes in a planar zigzag conformation, and PEO
crystallizes in a 72 helix with 7 ethylene oxide units completing two turns (Figure 5).
These features of the copolymer component can lead to competition between structures

and give rise to interesting copolymer properties.

49

 

The r
are of signifi

or for CIO\Sll

The
co- Jljmers
cnstil size
chain entar,

n
L

n
s

[hf IfllllViQr

$513315, T]

necrobiock c

‘1

pallifih-(rlens

4n:

n-
med Weft

Ii:
4:3: .
e L13 ll.

The regularly spaced double bonds in the unsaturated version of these copolymers
are of significance. They can be used as a site for branching to make grafted polymers,

or for crosslinking to form three dimensional network materials.

The characterization of copolymers is often complicated, and crystalline
copolymers are even more challenging. Molecular weight distributions, variations in
crystal size and perfection, the presence of interlamellar polymer chains and polymer
chain entanglements all add complexity to block copolymers. To aid in understanding
the behavior of these polymers, we synthesized a series of exact length triblock oligomers
with the generic structure H(CH2)X(OCH2CH2)yO(CH2)xH, where x = 6, 8, 10, 12, 14 and
16, and y = 2-8, 10, and 14. The blocks in these model compounds have the same
chemical components as the target polymers, but because they are simple low molecular
weight molecules, it is easier to test the origin of a specific property in the model
systems. These model compounds may provide simple rules for the study of (AB)n

microblock copolymers.

VI. Several polymers directly related to this project
1. Polyethylene and polyethylene oxide

Polyethylene is one of the most widely used commercial polymers. Unbranched
polyethylenes, or long chain normal alkanes, are of specific relevance to this project.
Linear alkanes with about 150 carbon atoms can form chain-folded crystals. There is a

marked preference for integral folding, whereby the fold length l adopts values z Un,

where L is the extended chain length and n an integer.80 As described earlier, crystals

50

with dit’t’erer
my long t
temperature.

Q ' “V
LQFlLIlZdllL

Obits-anon I
O'I'i‘fgroa {h _5
POlVI
five-3 "Obi;
Of The alkan:
0 eh‘l'homh:
r
‘Om‘ “'18 oh
“fire .
31.50 C

with different thickness can be obtained by using different crystallization conditions. For
many long chain normal alkanes, the crystallization rates depend on the crystallization
temperature, i.e. at a certain temperature below the melting temperature, the
crystallization rate reaches a maximum. Interestingly, by further lowering the
crystallization temperature a few degrees, the crystallization rates reach their minimum.
This effect is interpreted in terms of “self poisoning” of the crystal growth surface, i.e.

obstruction to chain extension by frequent deposition of the nearly-stable chain-folded
overgrowth.8 1
Polymorphism also exists for n-alkanes. There are four polymorphic forms for

crystals obtained under different conditions. Under all circumstances, the conformations

of the alkanes are trans planar zigzag (See Figure 5). The most stable form adopts an
orthorhombic unit cell with four chains parallel to the c axis.82 A different orthorhombic

form was observed by Khoury et (11.83 and Kobayashi et al.,84 in which the chains are

inclined with respect to the plane defined by the chain-ends. Two monoclinic structures
were also observed for n-alkanes.85a86 With different solvent and crystallization

conditions, different structures or mixtures of different structures were obtained.87

51

.2835038 32.: new $58 2835223 no mEBosbm .m oSwE

one—3333 Boa: mo 8303i

 

02x0 2835930; We ocaoeam

52

4 m2

 

 

 

 

 

32> mob

Another 7
chain normal 21} \
reproxirnately l
DSC rune star .
noisier X-ray l
intensiiely stud ;
angle X-ray sea :
The nature of t
close to the PE i
Chm ends dc.
iSIJmerization. ‘
gauche conform ,;

more in the 10,

\

DOW Changes to ~.

1
completely diso l

m .
prowl-lies 3U ~l

[re .

P013’etm l~

 

Another commonly observed phenomenon for unbranched polyethylenes and long
chain normal alkanes is their premelting behavior seen in DSC scans. Starting from
approximately 10 °C below the melting point of the polyethylene extended crystal, the
DSC curve starts to deviate from its baseline, and the longest d spacings shown in the

powder X—ray diffraction pattern continually decrease. This phenomenon has been
intensively studied by Raman and IR spectroscopy,88‘90 DSC,90’91 l3C NMR,91 small

angle X-ray scattering,92 and electron diffraction93 both individually and concurrently.
The nature of the transformation is summarized as follows. When the temperature is
close to the PE melting point, the regular packing of the end-groups is disrupted and the
chain ends develop a disordered state that allows trans-gauche conformational
isomerization. The inner methylenes still hold their all-trans conformation. As the
gauche conformations increase to a certain percentage, the whole chain can rotate and
move in the longitudinal direction. The original orthorhombic or monoclinic packing
now changes to hexagonal packing to allow the movements. Final melting is achieved by
completely disordering the trans conformation and disrupting the packing order. Changes
in properties such as d-spacings, and chain conformations can be observed during this

transformation.

Polyethylene oxide is a hydrophilic polymer ,with a broad range of commercial

applications. PEO has a very high salt affinity and therefore, can act as electrolyte host

for ion conducting polymers.94 It is also an important component in surfactants and food
additives. There are two major synthetic pathways for polyethylene oxides. The first,
known as oxyalkylation, is the polymerization of ethylene oxides in the presence of

LCWis acid or base catalysts. The products are viscous liquids to waxy solids with a

53

rarimum m«
polymenzatie
system. The
ailiine earth

real: as high

Pure l
305 i. b = l
helical stmen
tile: period (

tJOCCOI :.

maximum molecular weight of approximately 10,000. Another method involves the

polymerization of ethylene oxide on a catalytic surface in a heterogeneous reaction
system. The catalysts effective for the second reactions are alkaline earth oxides95 or
alkaline earth carbonates.96 The molecular weight by this polymerization method can

reach as high as 5,000,000.

Pure PEO readily crystallizes. The crystal has a monoclinic unit cell with a =
8.05 A, b = 13.04A and B = 125.4°. The PEO molecule in the crystalline state has a 72
helical structure, which contains seven ethylene oxide repeat units with two turns in the
fiber period of 19.3 A (See Figure 5). The internal rotation angles of this molecule are
1(OCCO) = 65° and ”C(CCOC) 2 188°, which correspond to the succession of a nearly
trans, gauche, trans conformation along O-C-C-O bonds. These structural features have
been confirmed by X-ray structure analyses as well as through extensive spectroscopic
studies.97'104 The origin of this conformation has been carefully studied and is

concluded to be due to the presence of a polarizable environment created by a
neighboring PEO chain, and not to some intrinsic conformational preference.105 Booth
et al.106‘108 studied macrocyclic polyethylene oxides and found that they also adopt the
same structure. PEO takes a planar zigzag conformation under tension. 109 As indicated

by X-ray diffraction and Raman spectroscopy,110 the planar zigzag molecule passes
through a triclinic unit cell, where the packing of the PEO chains is very similar to that of
monoclinic polyethylene. However, the planar zigzag conformation is stable only under

tension. When stress is removed, the planar zigzag modification disappears rapidly. PEO

54

also lame"

‘ W
resOiClITOll 1 "

The T,

:C. The melt:
trier. levels oi
perfect ensta
Homilies. l
femition of
poznts depen
annealing at
filial {lit mm.

Cllwils ffrm

also assumes various conformations in crystalline complexes with urea, thiourea,111

resorcinol112 and HgC12,1 13,1 14.

The Tg determined for high molecular weight PEOs are between —65 °C and —60

°C. The melting point of unfolded PEO increases with molecular weight up to 6,000 and
then levels off at a value of about 65 °C.115 The thermodynamic melting point of a

perfect crystal of infinite dimension has been calculated to be 76 °C.116 When PEO
crystallizes, both integer and non-integer chain folding are widely observed. The
formation of crystals with different lamellar thickness and therefore different melting
points depends greatly on the molecular weight, solvent and thermal history. With

annealing at different temperatures, isothermal lamellar thickening and thinning occur,
and the non-integer folded crystallites are converted to integer folded forms.117'123

Crystals formed from complexes of PEO and nitrophenol also show similar behavior. 124
2. CKEy nonionic surfactants and CXEOYC, amphiphilic triblock oligomers

Since n-alkyl chains and PEO adopt strikingly different structures in their
homopolymers, when they are connected to form a block copolymer they must compete
to obtain the conformation that best meets their energy and kinetic requirements. The
resulting molecular structures can have a planar zigzag conformation throughout the
molecule like crystalline PE, a helical conformation for the whole molecule like
crystalline PEO, or a planar zigzag PE segment and a helical PEO segment can coexist in

the same molecule. Such structures are most commonly seen in nonionic

surfactants.125v126 The simplest such surfactants have the general formula CH3(CH2)X.

I(OCH2CH2),OH (simplified as CxEOY). Their solid state structures have been studied

55

by Rirnan SP6
nonionic surf.
segment cont}
élyl chain le
compounds it
molecular er
onethflene

alrans eont't.
cozforrnatnv
rotnt. C .13.,

‘fipenning (
CK.Ffrinienn
‘Liphdllc gm
“ith the al

&\i3l3l.lj

A
1.1151ka O
Rana“
Hr’CH1-l“. (
CI“W :1
example,
an»

41011:

7"».
\m‘PiES‘

by Raman spectroscopy127‘130 and X-ray crystallography.131 In a study of a series of
nonionic surfactants where x = 1-16 and y = 1-8, Matsuura et al. found that the PEO
segment conformation depends not only on the oxyethylene chain length but also on the
alkyl chain length, and that there exists at least six distinctive conformational forms. For
compounds where x S 4, the conformation of the PEO segment is helical. For x 2 5, the
molecular conformation depends on the oxyethylene chain length; as the number of
oxyethylene units increases, the conformation changes from an all trans conformation to
a trans conformation for the alkyl and a helical conformation for the PEO segment. This
conformational transition takes place at m = 3-4. Being coincident with this transition
point, C3133, C1253, and C16E3 crystallize into either the extended form or the diblock form
depending on the crystallization conditions. Combined electron and X-ray diffraction
experiments show that for relatively long polyethylene oxide segments, (Figure 6) the
aliphatic and polyether segments segregate in bilayers stacked parallel to the chain axis,
with the alkyl chains tilted about 25-30° with respect to the polyethylene oxide helix

ax13,131,132

A related set of surfactants is a series of methylene-oxyethylene-methylene

triblock oligomers.100v133'139 Booth et a1.100,133-138 used X-ray, DSC, IR and
Raman spectroscopy to study triblock oligomers with the general formula
H(CH2)x(OCHzCH2)yO(CH2)xH, where y z 15, x = 1-18 and y = 9, x = 1-26. Booth
claimed that the crystallinity of each segment greatly depends on the segment length. For
example, in compounds with long alkyl chains, the center oxyethylene segment tends to
be amorphous while the alkyl chains are crystalline, and vice versa. For all crystalline

samples, the oxyethylene segment takes a 72 helical conformation as in polyethylene

56

oxide. and t
alkyl group
euiylene oxi

not of exact

In a
block is a fi;
3-7. the mo]
coordinate c
mnsheheat

Chain len 31h

Oil'fiiht lene
than that of

COnt-Omani)

oxide, and the crystalline alkyl groups take their usual planar zigzag conformation. The
alkyl groups are tilted about 24° from oxyethylene helical axis. No planar zigzag
ethylene oxide conformations were observed. Note that the ethylene oxide oligomers are

not of exact length which can affect the results.

In a solid state study140'143 of a series of triblock ABA’ oligomers where the A
block is a fixed length alkyl the length of the A’ group was varied, i.e. C8E4Cx, where x =
2-7, the molecular conformations were determined by spectral analysis based on normal
coordinate calculations. The conformations of these ABA’ compounds change from the
trans/helical/trans form to the fully extended form (trans/trans/trans) with increasing alkyl
chain length (x). The extended structure of the oxyethylene chain is stabilized for x 2 3. It
was suggested that the end alkyl blocks stabilize the extended structure of the
oxyethylene block in the triblock compounds when the length is comparable to or longer
than that of the oxyethylene block. The results of these studies demonstrate that the

conformation of the oxyethylene chain is affected strongly by the adjoining alkyl chains.

57

 

 

Figure 6. Solid state structure of surfactants CxEOy

58

 

3, Mic:

oligt

One
been stud.
oxyethylene
(Lilli-dii‘l’tftil
thioetnflenr
Tibiik‘lt Oll
“ere also
lluoethflent
particularly

dimd on I

3. Microblock copolymers containing oligothioethylene, oligoethylene and

oligooxyethylene

One structural analog of the exact length (AB)n microblock copolymers that have
been studied here are the copolymers of ethylene/thioethylene, 21, and
oxyethylene/thioethylene, 22. Mathias et al. used nucleophilic displacement of

0t,(i)—dibromides by or,(i)—dithiolates to prepare these hydrocarbon-thioethylene and

thioethylene-oxyethylene microblocks (shown in Scheme 17).”4’145 A group of
triblock oligomers with formula CH3(CH2)9(SCH2CH2),S(CH2)9CH3, where y = 1-5,

were also synthesized (Scheme 18). Litt et al. reported an interfacial route to

thioethylene-oxyethylene microblocks.146 The DSC scans of these materials are
particularly interesting and complicated, and often contain multiple transitions that

depend on the thermal history of the samples.

Like polyethylene oxide, polythioethylene also adopts a helical conformation, a 21
helix. The conformations along one repeat unit S-C-C-S are gauche-trans-gauche. The

tendency to form helical conformations in the thioethylene system is strong and has been

ascribed to strong dipolar interactions between C-S-C groups in adjacent chains.147

Because of the strong interaction, polythioethylene is insoluble in virtually all solvents

and melts at over 200 °C.148 For these polymers, a single exothermic transition was
observed between two endothermic transitions, and polarized optical microscopy
indicated that at least some order was maintained up to the highest melting transition.
Vibrational spectroscopy studies of the model compound with the shortest thioethylene
segment, CloESICm, showed that it adopted a trans conformation for the thioethylene

core. However, the remaining compounds all have helical thioethylene cores. The x-ray

59

diffractiOY
be attribut
' if C _£S
planar strt
tnonmkn
\ihritionul
‘ncreisingl
(IESCT_
unmamm
gauche C()n
gauche to t
similar to 1
Confl-‘mlillltf

nmemePE

diffraction patterns of the CIOESyClo series show no distinct low angle reflections that can
be attributed to a lamellar structure. In addition, two melting transitions are observed for
the C .0ES3C10 and C 10ES4C10 model compounds. Based on solid state NMR experiments,
planar structures were assigned for these models in the temperature range between the
two melting transitions. At room temperature, (below the lowest melting transition),
vibrational spectroscopy and NMR data indicate that the thioethylene segments are
increasingly dominated by gauche conformations as the length of segments increase. In
CmESzC 10, the conformation around the center S atom is gauche while the two external S
atoms adopt trans conformations as shown in Figure 7. Similar to the model compounds,
gauche conformations dominate in the (CXES2)n copolymers. A significant amount of
gauche to trans isomerization was observed close to the melting temperature, which is
similar to the PE premelting behavior. For the series of (BOXESy)n copolymers, the
conformations of the ES segments are similar to those in polythioethylene homopolymers

since the PEO chains are more flexible.

60

Scher

egnents

SChem

Scheme 17. Synthesis of microblock copolymers containing thioethylene

segments

HfsMRH + NaH

BKMBI, Br /\/ O\/\O/\/\Br

tetraglyme

21 22
x=3,5-8,y=2 X=1,y=2,3

Scheme 18. Synthesis of triblock oligomers CH3(CH2)9(SCH2CH2)yS(CH2)9CH3

Cl‘la(CHz)93r + H/(WSH

or

cmtceagscwcwct + H/i ,4 SH

benzene NaOH, H20

 

CHa(Cl‘|2)9(SCH2C|'12)yS(Cl'12)9Cl'b

y=1-5

61

4. n“

Lila
alkanes are
been sexer'.

backbones.

Dih
their melt
studies den
solid-solid
oligomers
latnella sur
lanella sot

rEported fr.
incompatih
F3211 git Mt;
01 Solution

lingure 8

{17111810011 3

4. fluorocarbon-hydrocarbon microblock copolymers

Like normal hydrocarbons and polyethylene oxides, perfluoroalkanes and normal
alkanes are two very different species both in terms of structure and property. There have
been several kinds of copolymers and oligomers that combine these two segments in their

backbones.

Diblock oligomers F(CF2)n(CH2)mH (FnHm for short) have been studied both in
their melt and crystalline phases by Raman and X-ray scattering experiments. DSC
studies demonstrated that the materials undergo at least one, and in some cases even two,
solid-solid phase transitions before melting. For relatively short alkyl chains, the diblock
oligomers form monolayer crystals in which the molecules are tilted with respect to the

lamella surface below the solid-solid transition and become arranged perpendicular to the

lamella surface above the solid-solid transition.149,150 Bilayer lamellar crystals were

reported for molecules with longer hydrocarbon segments and can be explained by the
incompatibility of fluorocarbon and hydrocarbon segments.149'153 Based on studies of

F 12H20, Moller and Hopken154 suggested a model for the crystal and transition behavior
of solution and melt crystallized samples. A highly ordered bilayer lamellar crystal
(Figure 8 left) forms when crystallized from solution, which can have a reversible
transition at 250 K that corresponds to the disordering of the alkyl chains with no change
in the fluorocarbon segment. At 308 K, the lamellar crystal is irreversibly changed to a
concentric cylinder crystal (Figure 8 right), which is the same as crystallized from melt.
These models can be used to explain the behaviors observed in DSC and solid state 13C

NMR experiments, and are also supported by SEM observations.

63

 

A St
Rabolt (’1 L
perfluoroal
conformatu
chain in pl;
Rarnan-aet
eharaeteris
occurs at t
1h: Whole
VET) Close
hldfocarb.
Chaims tilt
Infill Slate
effi‘Cll \‘e I)
SengntS
mush 11
the link
Ollggmers
tempefatt

A series of symmetric triblock oligomers FnHmFn have been studied intensively by
Rabolt er al.155'157 These materials are prepared by coupling an onto-diene with a

perfluoroalkyl iodide followed by dehalogenation (Scheme l9).156,158 The molecular

conformation is presumably the fluorocarbon in a helical conformation and the alkyl

chain in planar zigzag conformation. It was concluded156 from solid state studies of the
Raman-active longitudinal acoustical mode (LAM) that the vibrational frequency is
characteristic of the entire extended molecule and no decoupling of the chain vibration
occurs at the juncture between the helical and planar zigzag segments. This means that
the whole molecular chain is crystalline, the alkyl chain and the fluorocarbon chains are

very close to colinear, and the segments have similar vibrational modulus. For PEO-

hydrocarbon oligomers, the modulus of PEO is only 1/ 10 of the alkanes,134 the alkyl
chains tilt > 20° from the PEO helix axis, and the vibrations are more perturbed. In the
melt state, however, disordering of the hydrocarbon segment at the melting point
effectively decouples the longitudinal oscillations. With the two rigid fluorocarbon
segments still in their crystalline conformation, their frequency is perturbed by each other
through the hydrocarbon linkage when the link is short, but the perturbation is lost when

the link is long. Liquid crystalline behavior is also observed for these triblock

oligomers.157 While lacking the rigid mesogenic groups typical of liquid crystals, the
temperature range for them to form a stable smectic B liquid crystal phase is very small

— O.4°C below their melting points.

Scheme 1

Eli-rm] l
"“‘JbOn segt

 

Scheme 19. Synthesis of triblock oligomer FnHan

HgC=CH(CHz)m-40H=Cl-12 + F(CF2)nl

l AIBN

F(CF2)nCH2—-(|3H(Cl-|2)m-4(|3H—CI-|2(CF2),,F
I 1

l Zn,H+

F(CF2)n(CHz)m(CF2)nF

Scheme 20. Synthesis of microblock copolymers containing fluorocarbon and

hydrocarbon segments

HQC=CH(CHg)m-4CH=CHz + |(CF2)n|

l AIBN

{(CthnCHz—clgHtcmmipn—orig};

l BuaSnH, AIBN

{canteen};

65

Stuc

Chg

Copolymers of tetraflouroethylene and ethylene can be synthesized by bulk
copolymerization initiated by azo compounds.159 However, the structure obtained can

only be statistically controlled and the segments are short. Griffin et al.160’16l
described the preparation of a highly regular microblock copolymer containing
alternating fluorocarbon and hydrocarbon segments with precise block lengths. These
copolymers are similar in structure to our target molecules. The polymer was synthesized
by a modification of the routes used to prepare the di- and triblock semifluoronated
oligomers. The iodo compounds used were difunctional — or,w-diiodoperfluorocarbons
and the reduction step was completed with HSn(Bu)3 (Scheme 20). The ethylene

tetrafluoroethylene alternating copolymer crystallizes in an orthorhombic cell with four
parallel planar zigzag chainsl62’163 although calculations of the isolated chain indicate

that the most stable form is a 32 helix.164 As shown in Figure 9, having the
fluorocarbon next to the hydrocarbon in adjacent chains (rather than fluorocarbon on
fluorocarbon) is required to accommodate the cross sectional difference in this polymer.
Studies of the polymers synthesized by Griffin et al. show the formation of liquid
crystalline domains analogous to those seen in low molecular weight analogs. This
mesophase, caused by the rigidity of the fluorocarbon, extends from the melting point of
the alkyl segments to the eventual melting (disordering) of the fluorocarbon segments.
Thus, fluorinated (AB)n microblock copolymers correspond to a combination of hard and

soft blocks analogous to thermoplastic polyurethanes.

66

A - ..-~.-..—_, _

 

Figure 9. Solid state packing of polymer (CHzCHzCFzCF2)n

67

on;

a-

w:

int:

BIC

RESULTS

1. Synthesis and Purification
1. Acronyms for the compounds in this research

All compounds synthesized in this research contain two segments — an ethylene
oxide chain and either an n-alkyl or an n-alkyl chain with one double bond. For
simplicity in referring to these compounds, a nomenclature system similar to that
commonly used for PEO/PE surfactants is used in place of the full names of the
compounds. Thus, a methylene unit is abbreviated as C and the ethylene oxide repeat
unit as E0. The two methine carbons of the double bond are abbreviated as 1:. An

example of the naming protocol is shown in Scheme 21.
Scheme 21. Examples of acronyms for compounds

H(CH2)X(OCHZCH2)yO(CH2)xH
C,,EO,Cx
CH2=CH(CH2)x (OCHZCH2)yO(CH2)xCH=CH2
anEoycxrt
[(CH2)x CH=CH(CH2)x (OCHZCH2)y]n
(anCxEOyh.
[(CH2)x(0CH2CH2)yln

(CXEOy)n

68

2. Exact length oligoethylene glycols

Having sufficient amounts of exact length ethylene glycol oligomers is critical for

this research. Exact length oligoethylene glycols are commercially available up to 6

repeat units and we adopted a modified version of the approach of Keegstra et al.165 to
prepare glycols where y is 6-10 and 14. The route to these PEGs is outlined in Scheme
22. Monotritylation of selected glycols was achieved in bulk by treating a large excess of
the glycol with trityl chloride in the presence of pyridine. The monotritylate of the
glycols were then coupled with ditosylates of another glycol by treatment with NaH to
yield an extended ethylene oxide chain with both ends protected by trityl groups. The
glycols were de-protected through high-pressure hydrogenolysis with a Pd/C catalyst.

The overall yield for this five-step synthesis was > 90%.

The starting ethylene glycols for the syntheses were the commercially available
di-, tri— and tetraethylene glycols, while the resulting glycols were exact length glycols as
long as tetradecaethylene glycol. The selected glycol combinations used in this project
are listed in Table l. The main reason for these combinations is the commercial
availability of the starting materials, and considerations such as minimizing side reactions
were also applied. The tosylation reactions were carried out in a THF/water mixed
solvent system as shown in Scheme 23 to give exclusively the desired ditosylate

products.

69

Scheme 22. Synthesis of exact length oligoethylene glycols

TrCl

 

 

 

 

 

H(OCH20H2)XOH (excess) > H(OCHZCH2)XOTr
Pyridine
EOx
NaH/THF
Ts(OCHZCH2)yOTs ‘7
Tr(OCH20H2)x+yOTr e Na(OCH2CH2)xOTr
50 atm H2 Pd/C
v
H(OCH20H2)x+yOH
E02x+y
Scheme 23. Synthesis of oligoethylene glycol ditosylates
TsCl / KOH
H(OCH2CH2)YOH = Ts(OCH2CH2)yOTs
THF / H20
70

mot
\

Char

Silijil'
DU? 1'

Table l. Combinations of TrEOxH + TsEOyTs used in the synthesis of E02,...y

 

 

 

 

 

 

 

 

 

 

 

 

y
x 2 3 4 6
2 E06 E07 E08
3 E09 E010
4 E010 E014
3. Triblock amphiphilic oligomers—model compounds

The ABA triblock amphiphilic oligomers are a set of compounds with interesting
properties and serve as model compounds for understanding the polymer behavior. A
library of these oligomers CxEOny where x = 6, 8, 10, l2, 14, 16, and y = 2-8, 10, 14,
was synthesized. They were prepared by treating the appropriate glycol with NaH and 2
equivalents of the desired alkyl bromide (Scheme 24). The reactivity of the sodium salts
of di and triethylene glycols was low, probably because of the ease of forming a chelate
complex by the terminal oxygen atoms. The reaction mixtures were heated to the reflux
temperature of the solvent to facilitate the reaction for these two cases. Depending on the
molecular weight, the products ranged from viscous oils to waxy solids. Products with
short chain lengths were initially purified by distillation, and all samples were also
purified by low temperature crystallization. Because the solubility of the amphiphiles

changes with chain length, the short chain compounds (y = 2,3) were crystallized from

71

 

 

ct!
.
W4

‘3."
Utkk

C1—
-4-
.1.

..

r3.

Cm.
30h

36ft

0f]

1
6,39

acetone while the longer chain compounds (y = 4-8,10,l4) were crystallized from

methanol.
4. Monomers

The monomers, (x,o)-alkenyloligoethylene oxides where x = 2—4, 8, 10 and y = 6-
8, 10, 14, were prepared by coupling the sodium salts of alkenols and oligoethylene oxide
ditosylates (Scheme 25). The alkenols, 3-buten-1-ol, 4-penten-l-ol, 5-hexen-1-ol, 9-
decen-l-ol and lO-undecen-l-ol were purchased from commercial sources. The
oligoethylene oxide ditosylates and the corresponding oligoethylene glycols were

prepared as described earlier.

The monomers previously prepared by Qiao166 have shorter ethylene oxide
segments (y S 5), therefore they have lower boiling points and were purified by
distillation. The boiling points for the monomers prepared in this study are too high for
distillation, and new purification methods were used for purifying these monomers. The
crude monomer was first isolated by column chromatography to give yellow oils or
solids. All of the monomers were isolated as pure compounds except for the nConyCzn
series of monomers. These monomers were contaminated by structurally similar isomers
where the terminal double bonds were isomerized into internal double bonds allylic to the
ethylene oxides (CnCEOyCrtC). Further study is needed to find a better way to separate

the isomers or to restrict the isomerization reactions.

Because of the amphiphilic nature of the segments in the monomers, the polarities
of the monomers change with composition. The polarities of the eluents for

chromatography were adjusted accordingly and Table 2 shows the eluents used for the

72

corresponding monomers. The monomers were further purified under argon by stirring
them as hexane solutions (except for tetradecaethylene oxide series nCXEOMan, where
the solvent is toluene,) over a fresh sodium mirror followed by filtration through a funnel
packed with Celite® and acidic alumina. The purification set-up is shown in Figure 10.

All the purified monomers were stored in a drybox for future polymerization.

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 2. Eluents for purification of monomers (anEOnyn) by column
chromatography
y
6 7 8 10 14
75/25 EtOAc 90/10 90/10 90/10
EtOAc / EtOAc/ EtOAc / EtOAc/
hexanes MeOH MeOH MeOH
EtOAc 90/10 90/10 90/ 10 90/10
EtOAc / EtOAc/ EtOAc/ EtOAc /
hexanes MeOH MeOH MeOH
75/25 90/10 90/10 90/10 90/10
EtOAc / EtOAc / EtOAc/ EtOAc / EtOAc /
hexanes hexanes MeOH MeOH MeOH
50/50 75/25 90/10 90/10 95/5
EtOAc / EtOAc / EtOAc / EtOAc / EtOAc /
hexanes hexanes hexanes hexanes MeOH
50/50 75/25 75/25 90/10 95/5
EtOAc / EtOAc / EtOAc / EtOAc / EtOAc /
hexanes hexanes hexanes hexanes MeOH

 

73

 

Scheme 24. Synthesis of triblock oligomers CxEOyCx

NaH
H(OCH2CH2)yOH W Na(OC H20H2)yONa

EOy
CH3(CH2)x-1 BI’

CH3(CH2)x-1 (00112C H2)y0(CH2)x-1 CH3

CX EOny

Scheme 25. Synthesis of monomers anEOnyn

 

N H
CHz=CH(CHz)xOH a CH2=CH(CHz)xONa
THF
Ts(OCHzCl-12)yOTs

CH2:CH(Cl'|2)x(0CHzCl‘12)y(CH2)xCH=CHz

ncxeoycxn

74

@338 cougar—d 8898—2 .3 9.33

 

 

 

 

558 8:68

HOEOEOE

 

 

 

 

\

comb“

 

 

 

\

EH59?»

 

3.55

 

 

 

 

 

 

 

 

 

 

 

ESE goo—mom [Iv

 

 

 

 

:m u
2253 oeaeasfiu

 

 

 

...........

 

 

 

eoEoU

 

 

 

 

 

75

nil:

lief

b}-

18,7

5. Polymers
Unsaturated polymers (Cx1thEOy)n

The unsaturated polymers (erthEOy)n were synthesized by ADMET
polymerization of oligoethylene oxide or, (o-dialkenyl ethers using Schrock’s
molybdenum alkylidene catalyst 15. The polymerizations, generalized in Scheme 26,

were carried out on a 5 g scale for most polymers.

The catalysts were added as a solid to the liquid monomers; for monomers with
melting points higher than room temperature, they were melted and kept at about 50 °C.
As the catalyst dissolved in the monomers to give a yellow homogeneous solution,
ethylene gas was released vigorously. Since the monomers and polymers have high
boiling points, high vacuum was applied to the reaction system throughout this bulk
polymerization stage. When the polymerization became too viscous to stir, dry toluene
was added to lower the viscosity and vacuum was occasionally applied. The reaction
solution color changed from yellow to dark brown during the polymerization, presumably
due to partial decomposition of the catalyst. The polymerization progress was monitored
by periodically taking samples from the reaction and measuring their molecular weight
by GPC. Once the desired molecular weight was reached, the polymerization was

terminated by adding 1 mL of methanol.

Except for monomer nCzEOyCzrt, whose purification needs further investigation,
all monomers were polymerized to give high molecular weight polymers in good yield
(88% and above). The polymerizable monomers for this research to date are listed in

Table 3.

76

Sch

l'C‘ICIEO.‘

Scheme 26. Synthesis of unsaturated polymers (Cx1thEOy)n
sawtooth
X y X
flCxEOnyTE

1. Schrock Mo initiator
2. 50 °C, vacuum
I 3. toluene, 50 °C

NWT:

(executionn

 

Scheme 27. Synthesis of saturated polymers from unsaturated polymers

Monti.

(c,.II:c,.Iso,,)n

(0.30.1203.

5 atm H2 Pd/C

(C2x+2EOy)n

77

The polymer work-up procedure included precipitating the toluene solutions of
the polymer into hexanes and drying the isolated polymer under high vacuum until
constant weight was obtained. In order to obtain high molecular weight samples, some
polymers were fractionated by precipitation from THF solutions into methanol or
isopropanol. Since the polymer polarity changes with respect to the two segment

fractions, solvents for precipitation were adjusted accordingly. They are listed in Table 4.

Table 3. Monomers anEOnyrt polymerizable by ADMET polymerization.

 

 

 

 

 

 

 

 

y

x 2 3 4 5 6 7 8 10 14
2 +° i i i i i-
3 +° +° +° +b + + + + +
4 +3 +3 +3 +3 + + + + +
6 +3 +°

8 +b + + + + +
9 +° + + + + +

 

 

 

 

 

 

 

 

 

 

 

 

(+) monomer has been polymerized into polymer
(i) further purification investigation is necessary
a: polymers obtained by Jun Qiao

b: monomers available, small scale polymerizations were tested successfully

78

Table 4. Solvents used for precipitating polymers (anCXEOy)...

 

 

 

 

 

 

y
x 6 7 8 10 14

3 Hexanes Hexanes Hexanes Hexanes / Hexanes /.
iso-propanol iso-propanol

4 Hexanes Hexanes / Hexanes Hexanes/ Hexanes /
iso-propanol iso-propanol iso-propanol

8 Hexanes / Hexanes / Hexanes / Hexanes / Hexanes /
Methanol Methanol iso-propanol iso-propanol iso-propanol

9 Hexanes / Hexanes / Hexanes / Hexanes / Hexanes/
Methanol Methanol iso-propanol iso-propanol iso-propanol

 

 

 

 

 

 

 

 

Saturated polymers

Several saturated polymers (CxEOy)n, where x = 10, y = 6-8, 10, 14 and x = 20, y
= 7, were synthesized by reducing their unsaturated analogs as outlined in Scheme 27.
The reduction reaction involved the hydrogenation of the unsaturated polymer with H;

under catalytic conditions.

The hydrogenation reactions were carried out at room temperature at 5 atm H2
pressure with a 5 mol% catalyst loading. Complete reduction took approximately 5
hours. The molecular weights of the hydrogenated polymers are lower than their
unsaturated analogs. The cause of the decrease in molecular weight will be discussed in

the Discussion.

79

 

11

ot

in

11. Properties of triblock oligomers CxEOyCx
1. Thermal behavior

The thermal properties of triblock amphiphilic oligomers were analyzed by DSC
and optical microscopy. In DSC studies, most samples were heated to 100 °C to erase
thermal history, quenched to —100 °C at 200 °C/min, heated at 10 °C/min to 100 °C,

cooled to —100 °C at 10 °C/min, and finally heated to 100 °C at 10 °C/min.

Figure 11 shows a typical therrnogram for sample C14E03C14. The runs shown
are the heating and cooling scans taken after quenching the melted sample to —-100 °C.
As shown in the figure, the sample showed a sharp endothermic melting peak with an
onset at 42.7 °C, and upon cooling, a sharp exothermic crystallization peak with an onset
at 38 °C, several degrees lower than its melting point. No other thermal transitions were
observed for this sample. Since the C14EO3C14 molecule is small and simple, the heating

scan after quenching is the same as that obtained after slow cooling.

The rest of the DSC therrnograrns are shown as a series of stacked plots with each
plot containing ABA oligomers with the same alkyl length, but different ethylene oxide
segment lengths. For better comparison, the DSC responses are normalized to the same
sample weight. The temperature ranges of the plots are narrowed to include only those
regions where transitions were observed. The DSC scans shown in Figure 12, 13, 14, 15,
16 and 17 are heating scans of oligomers CXEOny where x = 6, 8, 10, 12, 14 and 16
respectively, taken after the samples were quenched to —100 °C. All samples showed
distinct melting endotherms. Some samples also showed exotherms before their melting
endotherms, which is an indication of crystallization during the DSC heating scan. The

endothermic peaks can be categorized in three types as shown in Figure 18. Type I is a

80

nellodeti
such Lb

Type 111
ones 0‘

Clldtlillt"

"/'"._ /_ /__ /‘,_'_/_.

/”:"

well-defined symmetric peak like that of C14EO3C14. Type II is a relatively broad peak
such as in C14EOloC14, where the lower temperature side of the peak rises gradually.
Type III is multiple melting endotherm such as in C14EO7C14. Table 5 summarizes the
types of peaks for each ABA triblock sample. Exotherms that appear before the

endotherm are also noted in the table.

Table 5. Summary of the types of DSC endotherms observed for ABA triblock

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

oligomers CXEOny.
y 6 8 10 12 14 16
2 II II I I II II
3 I II I I I I
4 III“ II II I II II
5 III I II I 11 H
6 II II3 I“ II“ II“ 111‘
7 II II III III III III
* 8 II II I II 11 11a
h¥ 10 I II II II II II
‘14 I H II II 11 H
R

 

a: exotherm observed before endotherm(s).

81

 

90

 

 

 

 

 

 

 

 

 

 

 

 

80 3
7o - 'l
60 d heating
0
g ____’
5: 50
g M
.C I
40 _ cooling
30 —
20 —
10 1 I I
-100 -50 O 50

temperature (°C)

100

Figure 11. DSC heating and cooling scans of triblock oligomer CMEOaC“

82

Heat flow, Endo ———>

 

CGEO1405

 

 

A C.~,EO1OC.~3

A 0650806

 

 

 

 

 

A CGEO7CS
4/\ C6E0606
CGE0505

M

 

M CGEO4CG

C6EOZCS

 

l l l

 

 

-40 -20 0 20 4O
temperature (°C)

Figure 12. DSC heating scans of triblock oligomers CSEOVCS

83

All .
OUCW 30: unwme

Heat flow, Endo _,

 

 

J1

03501403

 

CaEOmCa

CBEOBCB

 

 

CaEO7CB

 

 

CgEOng

 

 

A
J1
/J\
J1

CBEOSCB

 

 

CBEO4C8

 

 

 

Jl
J

C8E03C3

0350208

 

 

 

l

 

-1 0 O 1 0 20
temperature (°C)

30

40

Figure 13. DSC heating scans of triblock oligomers CBEchs

84

50

Heat flow, Endo ——>

 

A cloeoucio

 

 

C1OE010010

 

CiOEOBCw

 

 

 

010507010

 

 

010506010

 

 

C1OEOSC1O

 

 

C1OECD4C1O

 

 

 

 

C10EOaC10

 

J1.
J\
J\/\
J
Jl
J
A
1 A 1

010502010

 

 

 

 

1 O 20 30
temperature (°C)

40

50

Figure 14. DSC heating scans of triblock oligomers CmEOwa

85

 

 

— .r—n— ——--

Ohvcm (so: «am:

 

Heat flow, Endo —>

 

 

C12EO14C‘12

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

#_/\

A C1215010012

C12EOBC12

A C12EO7012

A C12EOGC12

A C12505312

A C12E04012

j\ 012503012

A C12EOZC12

1O 20 30 40 50

temperature (°C)

60

Figure 15. DSC heating scans of triblock oligomers C12EOVC12

 

 

thu 3:: «Panel

 

 

Heat flow, Endo ———>

 

 

01412014011

C145010014

 

 

C14EOBC14

 

 

01450794

 

 

C14EOGC14

 

 

 

V

 

C14EOSC14

C14E()4C14

 

 

 

 

C14503014

 

C14E()2(314

 

 

 

 

10

J1

Jl/1
J1
J.
J1
J1
#1 ,

20 30
temperature (°C)

60

Figure 16. DSC heating scans of triblock oligomers CuEOYC“

87

 

 

OCCW (50: ~59:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

016E014C16 A
0155010016
4./\
Cieancie
/\
i CIGEOIC... A
o
'0 wt
::
LIJ
e;
f CtGEOSCtfi
In
a)
I
6161205016 J1
C16E04C1e / 1
0161203016 A
016E02016 A
10 20 30 40 50 60

temperature (°C)

Figure 17. DSC heating scans of triblock oligomers C15EOVC15

88

 

 

 

 

Flt

type ' type II type III

. 21 J

Figure 18. Types of DSC endotherm peaks seen for triblock oligomers

 

 

heat of fusion

 

/ \ melting point

Figure 19. Melting point and heat of fusion measured by DSC

89

also of
onset
lines I
consist
endoth
[ONES

a the

The melting points Tm and heats of fusion AHfus for these triblock oligomers were
also obtained from DSC measurements. As shown in Figure 19, the Tm was taken as the
on-set of the melting endotherm, which can be obtained by finding the intersection of the
linear portion of the low temperature side of the peak and the baseline. This method is in
consistent with the calibration of the DSC equipment. Except for samples with type III
endotherms, which show solid-solid transformations, Tms measured in this way also
correspond well with the results from polarized optical microscopy, where Tm is defined
as the point of total loss of sample birefringence under polarized light. The Tms of these
54 triblock oligomers are shown in Table 6. The heats of fusion, indicated as the shaded
area under the endotherm in Figure 19, are reported in Table 7. The Tm and AHfus trends

will be discussed in the Discussion section.

90

I \l

Table 6. Melting points (°C) of ABA triblock oligomers CXEchx.

 

 

 

 

 

 

 

 

 

 

 

 

y 6 8 10 12 14 16

2 -25.9 -l.9 19.5 31.6 41.5 50.1

3 —16.l 5.0 22.0 33.6 42.7 50.9

4 -21.7, -19.3 3.6 19.4 33.4 42.0 48.6

S -18.1, —l3.8 9.3 21.4 32.8 41.1 46.9

6 -11.5 0, 6.4 21.8 31.2 40.2 46.4

7 -2.6 9.4 18.5, 22.8 28.6, 31.9 38.1, 40.9 44.6, 48.1
8 2.2 13.6 23.7 30.9 38.8 41.4
10 15.7 21.1 26.7 35.0 40.5 43.6
14 26.5 26.0 35.5 38.5 43.5 47.5

 

 

 

 

 

 

 

 

91

Table 7. Heats of fusion (J/g) of ABA triblock oligomers CxEOny.

 

 

 

 

 

 

 

 

 

 

 

 

X
y 6 8 10 12 14 16
2 100 107 160 178 173 190
3 147 152 156 194 194 207
4 104 129 138 175 190 164
5 112 151 151 179 186 185
6 32 112 144 167 180 169
7 97 123 144 143 165 184
8 31 110 140 151 153 107
10 138 118 136 133 150 118
14 127 114 129 124 129 134

 

 

 

 

 

 

 

It was noted that many samples showed double melting behavior in the DSC
heating scans, especially for the series of triblocks with 7 ethylene oxide units. These
multiple transitions indicate that multiple crystal forms exist in these samples. The DSC
heating scans of this series after flash quenching were re-plotted in Figure 20. We can
see that for x _>. 10, all of the DSC scans showed double melting transitions. For x = 6

and 8, no double melting observed, but the peaks were significantly broadened. Because

92

 

of i

201

ct;

of its interesting behavior, this series was studied in more detail. Sample C14EO7C14 is a
good representative of this series and thus was chosen for most of the detailed

experiments.

A series of controlled experiments were carried out on C14EO7C14. One study
was the convertibility of those two peaks in DSC. It was observed that the higher melting
peak diminished with increased holding times at 50 °C, above the sample’s melting point
(41 °C). The melt-quenched sample was held at 35 °C, a few degrees below the lower
melting point of the sample for different periods. The sample was then heated and its
DSC heating scans was recorded as shown in Figure 21. As shown in the figure, the
lower melting peak gradually converted to the higher melting peak as the annealing time
became longer. This set of experiments showed that the two crystal forms obtained from

melt crystallization can be interconverted. Details will be discussed later.

The C14EO7C14 sample was also tested to see if solvent will affect the structure of
crystal formed from solution. Samples was crystallized from methanol and hexanes
respectively and the DSC heating scans were recorded on samples from room
temperature and are shown in Figure 22. The DSC traces for these two samples are

different, with the sample crystallized from hexanes melting at 39 °C, (AHfus 164 J/g,)

and the sample crystallized from methanol melting at 41°C, (AHIus 169 J/g).

93

 

 

C16EO7C16 l,‘

 

Heat flow, Endo—9

 

014507014

 

0111507012 J11

 

0.0507010 Jill

 

l l 1 1

 

-20 0 20 40
temperature (°C)

Figure 20. DSC heating scans of triblock oligomers C,,EO7Cx

94

 

 

 

 

 

 

 

 

 

 

 

I /\/\ 25 min

20 min
0
'U
C
1.11

52?. 15 min
‘5
m
:I:

10 min

5 min

0 min

35 4O 45 50

temperature (°C)

Figure 21. DSC heating scans of triblock oligomers c14E07C14 annealed at
35 °C for indicated time

95

heat flow, endo

 

from hexanes solution

 

 

from methanol solution

 

 

 

T I T T T T

20 3O 40 50 60 70 80 90
temperature (°C)

Figure 22. DSC heating scans of triblock oligomers C14E07C14
crystallized from different solutions.

96

 

100

 

IQ

2. Powder X-ray diffraction

Characterization by powder X-ray diffraction (XRD) was performed for most of
the triblock oligomers. The low angle powder XRD pattern of oligomer CmEOng, a
typical sample of an oligomer with a short ethylene oxide segment, is shown in Figure 23
and the higher angle data in Figure 24. In Figure 23, the well-defined series of 001 lines
indicates a layered structure was formed. The layer spacing was calculated using the

Bragg equation (equation 14) to be 51.3 A based on the 001 d-spacing.
d = l/Zsin 6 eq. 14

In Figure 24, in addition to the 001 peaks that extend to higher angles, several
peaks shown between 19° and 30° are very important in determining the crystal unit cell
and detailed packing. An analysis and comparisons based on these peaks will be made in

the Discussion.

For comparison, the XRD profiles of the series of triblock oligomers CMEOyCu
(y = 2-8, 10, 14), obtained by solution crystallization are displayed in Figure 25 for lower
angles and in Figure 26 for wider angles. All of these samples have well—defined 001
series peaks at lower angles (Figure 25), which confirms that all of the triblock
oligomers have lamellar structures in their crystalline phase. One can also see that the d-
spacing (best indicated by the first peak) became longer as the length of the ethylene
oxide segments increased, except for y = 7 and 8. The calculated d-spacing values are
listed in Table 8. In wide angle XRD profiles (Figure 26), the diffraction patterns are
similar for samples with y = 2-7 and also for y = 8, 10, 14. This suggests that the crystals

mainly exist in two kinds of packing formats.

97

relative Intensity

 

 

 

x10

 

 

 

 

 

 

 

20

Figure 23. Low angle XRD for C16E03016.

98

13

15

 

 

 

 

intensity

 

 

 

 

 

 

 

 

 

 

 

 

 

1 5 20 25 30 35
2 0

Figure 24. Wide angle XRD for C15E03015.

99

40

45

intensity

“ g>F>>
l

 

hi 0 C145010014
__A _A A A

 

 

(>

C14509014
J13") JLLA 4g 2

014508014

x10
A )1 A A A A

A

x10 C111E070»:

 

 

>>
I

I

I

x10

 

 

X10 C14505014

 

C14EO4014

 

x3 C141E02C14

 

 

 

 

 

03
U1
\1
(O
—L
.5
.5
W

2 6
Figure 25. Low angle powder XRD of triblock oligomers CuEOyC“.

100

15

intensity

 

 

 

 

 

C14EO14C14

C145010014

 

014508014

C14EO7C14

C14E06C14

C14E05014

C14EO4C14

C14EOSC14

C14502014

 

 

15 20

26

25

30

Figure 26. Wide angle powder XRD of triblock oligomers C14EOYC14.

101

intensity

“99>
I.
I

 

x10
,1 1 C16E014C16

x10

 

C14EO14C14

A ’/\_______. .

x5
C125014012
x5
(3105014010
A

081501403

 

 

 

 

 

 

 

 

 

 

 

I\)
(.0
A -
U1
0)
\1

Figure 27. Low angle powder XRD of triblock oligomers CXEO14Cx.

102

 

 

intensity

 

 

 

C:16EC)14C:16

 

C14EO14014

C12EO14C12

C:10EO14C1O

 

CBEO14CB

 

061501406

 

 

15 20

20

25

 

30

Figure 28. Wide angle powder XRD of triblock oligomers c,so,..c,,.

103

Table 8. d-spacings (A) for triblock oligomers (CMEOyCM) with tetradecyl alkyl

 

 

 

 

segments.
y 2 3 4 5 6 7 8 10 14
d (A) 41.3 46.4 48.7 53.1 54.4 60.1 57.7 64.5 75.1
Ad (A) - 5.1 2.3 4.4 1.3 5.7 -2.4 -

 

 

 

 

 

 

 

 

 

 

The XRD scans for a series of triblock oligomers CxEOqu, with a constant
ethylene oxide block length of y = 14 and x = 6, 8, 10, 12, 14 and 16 are shown in Figure
27 (lower angles) and 28 (higher angles). The XRD pattern for all the samples in this
series are similar from 20 to 30° 20 values, while in the lower angle portion, the d-
spacing increases as the alkyl segments become longer. However, the increase in the
increments Ad, defined by the d-spacing differences between the samples with values of x

and x+2, are not linear. Their values are tabulated in Table 9.

Table 9. d-spacings (A) for triblock oligomers (CXEOMCX) with

tetradecaethylene oxide segments.

 

 

 

 

 

x 6 8 10 12 14 16
d (A) 56.2 55.1 61.9 65.5 75.1 84.0
Ad (A) - -1.1 5.7 9.3 18.9 28.2

 

 

 

 

 

 

 

104

 

C14E07C14

As we already seen from DSC studies, triblock oligomers with 7 ethylene oxide
units show the most interesting behavior. As in the DSC studies, we chose C14EO7C14 as
a representative oligomer for most of the XRD studies. Other samples in this series were
also tested and were found to behave similarly to this compound. This compound was

subjected to a series of experiments to identify the structures and their transformations.

The first issue we focused on was the different structures that form when
C14EO7C14 is crystallized under different conditions. Powder XRD experiments were
performed on samples obtained by crystallization from methanol, from hexane, from the
melt with a slow cooling rate to room temperature, from the melt after fast quenching to
subambient temperature, and by self-seeded isothermal crystallization from the melt close
to the equilibrium melting temperature. Figures 29 (low angles) and 30 (wide angles)
show the XRD data from samples obtained by crystallization from solutions, and by slow
and fast cooling from the melt. All of the samples show characteristic lamellar behavior
as evidenced by the well-defined 001 peaks. Their d-spacings were clearly different, with
crystallization from methanol solution resulting in the longest, 60.1 A, crystallization
from hexanes solution the shortest, 52.7 A, and the two melt crystallization results in
between, 54.6 A from slow cooling and 56.3 A from fast quenching. Their high angle
diffraction patterns were also quite different. The flash quenched sample has a pattern at
20 = 19.7° and between 225° to 27° that is similar to that obtained from methanol.
However, small peaks at 186° and a shoulder at 193° seen in the flash quenched sample

also match peaks in the slow cooled sample. Crystals obtained from hexane bear the least

105

resemblance to the other samples. These results indicate that the samples crystallized

under different conditions do give very different crystals.

To further test the melt crystallized sample structure change with sample history,
we carried out another set of experiments. The sample was melted and held at 100 °C for
one hour to totally randomize any ordering in the melt sample, quenched to liquid
nitrogen temperature, and then was allowed to warm up to room temperature in a
desiccator to prevent moisture build up. The XRD pattern of the sample was taken
immediately, after 3 hours and after 15 hours. Their profiles are given in Figures 31 and
32. From Figure 31, we can see that the lowest diffraction angle, initially at 158° and
corresponding to a d-spacing of 56 A, shifted to lower angles after 3 h at room
temperature, and finally shifted to an angle that corresponds to the d-spacing given by
sample crystallized from methanol, 60.1 A. From their higher angle diffraction profiles,
we observed the change of their XRD pattern from one that is quite similar to that of
samples slowly crystallized from melt, to one like that obtained from methanol. It seems

that the crystal form obtained from methanol is the most thermodynamically stable form.

To further test this hypothesis, we used self-seeded isothermal crystallization to
obtain the most stable crystal from the melt. Self-seeding was achieved by carefully
melting a crystalline sample until only a few tiny crystalline needles were seen under a
polarized microscope. The system was then held at less than 1 °C below the crystal
melting point for crystals grow. By doing this, only the most thermodynamically stable
crystal seeds exist, and the only crystal that forms during crystallization are these with the
structure of the seed. The crystal thus obtained was characterized by XRD over a period

of 2 months to test its stability. The XRD results taken immediately after the crystal was

106

obtained, after being stored at room temperature for 2 days, and after 2 months are shown
in Figures 33 and 34. As can be seen from both figures, there was no change during this

storage period. This phenomenon was also confirmed by Raman and IR spectroscopy.

We also performed an experiment to test the isothermal conversion of one crystal
form to another above room temperature, which is similar to the DSC experiment
described earlier. The sample was flash quenched from the melt to liquid nitrogen
temperature, and then quickly heated to 35 °C. Diffraction patterns were taken at low
angles as a function of time. As can be seen in Figure 35, the sample’s highest peak,
originally at approximately 164°, shifted to a lower angle. At 14 min, this peak had
diminished while a new peak at 154° emerged. Eventually, all of the sample was

converted into the stable high temperature form.

107

 

from melt fast cooled, d=56.3A

 

L x10
M

from melt slow cooled, d=54.6A

 

 

0

k g

1....4’” A

Intensity

g

from hexanes, d=52.7A

 

x10
L 4.4/AL

from MeOH, d=60.1A

x10
~& 4

 

 

 

_. g

2 3 4 5

 

Figure 29. Low angle powder XRD of 6145076“ crystallized by different

methods.

108

 

 

 

 

 

mtensnty

 

 

 

WJ

 

Wmelt fast cooled

from melt slow cooled

 

from hexanes

from MeOH

 

 

 

15

l

20

29

25

30

Figure 30. Wide angle powder XRD of C14EO7C14 crystallized by

different methods.

109

intensity

 

14 hours

3 hours

 

 

 

 

 

0 hour

 

29

Figure 31. Low angle powder XRD of C14EO7C14. Crystal obtained
by flash quenching from the melt, then holding at room temperature

for the periods of time as indicated.

110

 

 

 

 

14 hours

 

intensity

 

 

N 3 hours

 

 

 

JV 0 hour

I

1 5 2O 25 30
2 6

 

 

 

Figure 32. Wide angle powder XRD of C14E07C14. Crystal obtained by

flash quenching from the melt, then holding at room temperature for the
periods of time as indicated.

111

 

 

 

/ L stored at room temperature for 2 months

A 2.. J

intensity

 

 

__.... A

J "L stored at room temperature for 2 days

 

 

K] L right after crystallization

 

 

20

Figure 33. Low angle powder XRD of C14EO7C14 crystals obtained by
isothermal crystallization at 41.5 °C.

112

 

 

 

 

 

intensity

 

 

 

 

 

 

M

l

 

i

15 2O 25
2 9

Figure 34. Wide angle powder XRD of C14E07C14 crystals obtained by

isothermal crystallization at 41.5 °C. Bottom: crystal tested right after
obtained. Top: crystal stored at room temperature for two months.

113

 

 

intensity

—F

M ‘ 135 min
A
A ‘A “ ‘A“ ‘ A

A A
AA A A. A“‘ A“A“AAA ‘

0 +4. + 60min
+ +++++++++++++++4

T

AA 00
’ o o o 0 ' o ’ .

14min
A‘AAAAAA.A.AA

9 .II. 7min
I
I I I I I I I I I .

 

°°0. 0min

 

 

l l l

1.6 1.7 1.8 1.9 2
29

Figure 35. Powder XRD evolution of C14EO7C14 annealed at 35°C.

114

3. Spectroscopic characterizations

Spectroscopic tools including 1H NMR, '3 C NMR, FT IR and Raman spectroscopy
were used to characterize the triblock oligomers. Detailed spectroscopic data such as the

NMR spectra appear in the Experimental section, and are not repeated here.

IR and Raman experiments which can show the details of molecular structures
such as packing information and molecule chain conformations, were used to elucidate
the triblock oligomer structures, especially that of C14EO7C14, which showed interesting
multiple crystalline phases. Samples for IR and Raman experiments were prepared either
by melt crystallization on a substrate, or by depositing the desired oligomer as a solution
onto a polished silicon slide, and evaporating the solvent to dryness in a moisture free

environment.

The IR spectra for CxEOyCx where y S 6 are similar. A typical spectrum of
C14EO3C14 is shown in Figure 36. Specific attention was paid to the low frequency
region since it contains useful information about crystal packing and molecular
conformation. For example, the band at 718 cm‘1 in Figure 36 can be assigned to planar

zigzag alkyl chains packed in a triclinic unit cell.

Samples with 7 ethylene oxide units, CXEO7CX, crystallized under different
conditions had different spectra. Figure 37 shows the IR spectra of C14EO7C14
crystallized from hexanes and methanol. It can be seen that the two spectra are quite
different in the low frequency region. Samples crystallized from hexanes showed bands

at 1147, 1111 and 851 cm’1 which are characteristic for low frequency PEO in a helical

115

conformation. 100,101 The bands for samples obtained from methanol are very similar to

that Of C14E03C14.

Raman spectra were also taken of the two C14EO7C14 samples. Again, their
spectra were very different (Figure 38). Bands at 1042, 1150, 1275 and 1497 cm],
which are known to be characteristic of planar zigzag PEO, were observed in spectra of
samples crystallized from methanol, while bands at 854, 864, 1002 and 1484 cm'1 for

helical PEO were observed in spectra of hexane crystallized samples.

Crystals of melt quenched C14EO7C14 were monitored while stored at room
temperature for several days (Figure 39). From the Raman data, it can be concluded that
the melt-quenched sample first adopted a helical conformation for the PEO segment and
then changed to a planar zigzag conformation. This is indicated by the obvious change in
the Raman spectra between days 2 and 4. Crystals obtained from melt quenched
C14E014C14 sample, however, did not show such a change. As shown in Figure 40, the
spectra for this sample were virtually the same through out the test period—indicating

that the PEO segment maintained a helical conformation.

116

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8 days

 

 

A 4 days
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5.5,
Q
(I)
C
2
.E
2 days
as obtained
0 500 1000 1500

Raman shift (cm")

Figure 39. Raman spectra of C14E07014. Samples were obtained by

quenching from the melt, and stored at room temperature. Spectra were
taken at the time intervals indicated in the figure.

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121

III. Properties of unsaturated (AB)ll microblock copolymers (C,,1I:C,,EO,)n
1. Physical properties

The molecular weights and polydispersity indexes (PDI) of the unsaturated
polymers are collected in Table 10. Our target molecular weight for the polymers was
50,000 g/mol and most polymerizations met that target. PDI values for polymers
obtained after precipitation in hexanes were near 2, typical for step-growth
polymerizations. Despite attempts to remove all catalyst residues, the purified polymers

had a slight yellow to green tinge, which is believed to be due to catalyst residues.

Because of the amphiphilic nature of the two segments, the polymers are soluble
in an unusually broad range of organic solvents, including polar and non-polar solvents.
The solubility depends on the segment lengths. Polymers with long alkenyl segments and
relatively short ethylene oxide segments are more soluble in non-polar solvents such as
toluene and carbon tetrachloride and are even slightly soluble in normal alkanes. In
contrast, polymers with an opposite ratio of components (short alkenyl segment, long
ethylene oxide segment) are more soluble in polar solvents such as chloroform, ethyl
acetate, acetone, acetonitrile and methanol. Polymers (C31IC3E014)., and (C41tC4E014),.
are even soluble in water because of their long ethylene oxide segments. Solvents like
THF and dialkyl ethers that contain both polar and non—polar groups, can dissolve all of

the polymers.

122

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 10. Molecular weights and PDI values of unsaturated polymers
(C,1tC,E0,),,."

Polymer Mn PDI Total yield (%)
(C31tC3E06)., 25,500 1.71 85
(C41tC4E06)., 48,800 1 .84 97
(CgithEOQn 58,500 1 .41 84
(C91tC9E06),, 67,800 1 .56 89
(C31tC3EO7)., 26,400 1 .89 98
(C41tC4E07)n 55,500 1 .79 98
(CurthEO7)n 58,300 1 .40 8 1
(C91tC9EO7)n 40,600 1 .41 85
(C31tC3EOg)n 47,200 1.73 95
(C41tC4E03),, 19,400 1 .61 85
(anCsEOg),, 65,700 1 .46 94
(CgrthEog)n 60, 100 1.5 1 9 l
(C31tC3EOm)n 54,500 1.57 97
(C41tC4E010),, 98,500 1.38 95
(CgtthEOm)n 41 ,300 l .74 99
(anCgEOm)n 52,700 1 .46 99
(C31tC3E014)n 17,400 2.00 97
(C41tC4E014)n 41 ,700 1 .52 98
(CansE014)., 21,100 1.87 93
(C91'CC9E014)“ 63,200 1 .64 97

 

 

a. The molecular weights refer to the highest molecular weight portion if the
sample was fractionated. Yields are the total yield after precipitation from hexane.

123

2. Morphologies of unsaturated polymers

All of the polymers are crystallizable, but some polymers have melting points
below room temperature. Thus at room temperature, polymers (CxtthEOy)n where x = 3
and 4, y = 6-8 are amorphous, while all of the other polymers are crystalline.
Micrographs of the crystalline polymers under cross-polarized light are shown in Figures
41 to 45. All of the crystallized polymers form spherulites as indicated by the
characteristic Maltese cross pattern, however, many of the samples differ in the details of
their morphologies. Both polymers (CarthEog)n and (C91IC9EO.;)n crystallized as
banded spherulites as shown in Figure 41 with similar small band widths. Polymers
(Cg1thE07)n and (C91tC9EO7)n also crystallize as banded spherulites (Figure 42),
however, the band widths were quite different, with the bands of (CgithEO-y)n about 30
times that of (anC9E07)n. Polymers crystals from (CgithEOg)n and (C91tC9EOs)n also

were banded spherulites (Figure 43) with the band width larger for (anCsEOg)...

Polymers in the (anCXEOlo)n series crystallized differently. As shown in Figure
44, (C31tC3EOm)n formed banded spherulites while (anCxEOm)n polymers where x = 4,
8 and 9 crystallized sluggishly. Polymer (C41tC4EOm).. needed to be sheared to induce
crystallization into ill-defined spherulites while polymers (C31IC3EOm)n and
(C91tC9EOm)n crystallized into tiny banded spherulites after an extended time at room
temperature. For polymers with 14 ethylene oxide units, none showed banding and the
spherulite sizes were relatively large (Figure 45). Normally, the bands of the banded

spherulites are visible under cross-polarized light, but not under normal light. For most

of the banded spherulites in this study, the bands can be clearly seen without cross-

124

polarized light. Shown in Figure 46 is a micrograph of a banded spherulite sample of
(Cg1thEO7)n taken without cross-polarized light. The bands are clearly seen and can be
compared to the same sample in Figure 42. Similar observations were reported for PEO
samples and were ascribed to the step-growin g or spiral-growth of spherulites rather than
from lamellae twisting.28 Further studies need to be carried out to clarify the cause of

banding in (C,.1CC,,EO,)u spherulites.

125

 

Figure 41. Micrographs of polymers (anCgE05). (left) and (C91IC9E06)u (right) under
cross-polarized light

   

- w ‘
,oc‘
_
r a}, ,
0:534 5

n9 ‘ s ‘
#Agttfu a -

Figure 42. Micrographs of polymers (Can3E07)n (left) and (C91rC9EO-7).. (right) under
cross-polarized light

126

 

Figure 43. Micrographs of polymers (CsTCCsEOs)n (left) and (C9flC9EOs)n (right) under
cross-polarized light

 

Figure 46. Micrograph of polymer (C31CC3EO7)n under non-crosspolarized light

127

 

 

Figure 44. Micrographs of polymers (C31tC3EOlo).. (upper left), (C41tC4EOm).. (upper

right), (CgtthEOMn (lower left), and (C91cC9EOm)., (lower right) under cross-polarized

light.

128

 

Figure 45. Micrographs of polymers (C31tC3E014)n (upper left), (C41tC4E014).. (upper
right), (ngrthEOm)n (lower left), and (C9WC9E014)n (lower right) under cross-polarized

light.

129

3. Spectroscopic characterizations

Since the polymers are homologous, their NMR spectra look very similar to each
other. For example, all have resonances in three main regions of the 1H NMR spectrum
— methylene protons of the alkenyl segments at 1.4—3.5 ppm, methylene protons of the
ethylene oxide segments at 3.5-3.7 ppm and the methine protons for the double bonds at
5.3-5.5 ppm. The methine protons can be used as quantitative indicator for the degree of
polymerization. As the polymerization proceeds, the peaks shown at 5.8 and 4.9 ppm for
the terminal double bonds gradually disappear, while peaks emerge at 5.4 ppm
corresponding to the internal double bonds. This change means the cam-diene monomer
was converted into oligomers and then to polymers. Similar transformations were also

observed in '3 C NMR and FTIR spectroscopy.

IR spectroscopy was also used to study the polymer conformation changes.
Polymer (C9KC9EO7)D was crystallized from the melt, hexanes and methanol, as was
done for the C14EO7C14 sample. However, as shown in Figure 47 (only the low
frequency region is shown), the spectra are basically the same for each sample. This
indicates there are no significant conformational differences for polymer chains

crystallized under different conditions.

130

 

 

absorption

it
is; \mJ/‘l‘./’1A\JWK

 

f”)

f
l
l
l
i

W}

l

‘t

\

fail, from hexanes

g

V ‘1
\wtgmwfi

from melt

in"

 

from methanol

 

 

 

1400

1 200

wave number (cm")

1000

800

600

Figure 47. Low frequency region IR for polymer (C,,1tC.‘.E07)n crystallized

using different methods.

131

4. Thermal behavior of the unsaturated polymers

The unsaturated polymers were analyzed by DSC to characterize their thermal
properties. Each sample was originally crystallized from the melt at room temperature
for at least one month to allow full crystallization. All samples were first heated at 10
°C/min from 20 °C to 105 °C and then held at that temperature for 5 minutes to allow
complete randomization of the polymer sample. The sample was then quenched to —100
°C at 200 °C/min, heated at 10 °C/min to 100 °C, cooled to —100 °C at 10 °C/min, and

finally heated at 10 °C/min to 100 °C.

Shown in Figure 48 to 51 are the heating scans taken after flash quenching the
polymers to —100 °C. The data presented are for polymers with the same alkenyl
segment length, i.e. polymers (anCxEOy)n where x = 3, 4, 8, 9 respectively. All of the
polymers show Tgs at low temperatures. Their values are shown in Table 11. As shown
in Figure 48 for polymer (C31IC3E06).., the scans are complicated. A Tg at —58 °C, is
followed by an exothermic crystallization at —49 °C and three overlapping melting and
crystallization peaks. One crystalline phase melts, which is then followed by two
alternating crystallization and melting processes as the temperature increases. Polymer
(C31tC3EO-7)n showed similar multiple melting and crystallization behavior except there
was no low temperature crystallization exotherm. Polymer (C31tC3E03)n showed one
major melting endotherm followed by a small endotherm. Polymer (C3TCC3EOm)n only
showed one broad endothermic peak, and polymer (C31tC3E014)n showed a narrow
endothermic peak. Polymers in the (C41tC4EOy)n series with y = 6-8 showed melting
transitions on both sides of a crystallization transition, while polymers with y = 10 and 14

only showed single endotherms (Figure 49). Polymers in the (anCgEOy)n series

132

followed the same trend as that of the previous series, except the second endotherm for
polymer (CgtthEOg)u was very small (Figure 50). Polymer (C91tC9E06)n showed three
endotherms with exotherms between each endotherm (Figure 51), like that of its analog
in (C31tC3EOy).. series. Other than this sample, the rest of the samples had DSC

transitions that resembled their homologs of the previous series.

Table 11. Glass transition temperatures (°C) of the unsaturated polymers (C,,1I:C,,EO,)u

 

 

 

 

 

 

y
6 7 8 10 14
-57.5 -53.3 -57.7 -65.4 -58.5
-55.8 -67.2 -56.6 -65.1 -55.5
—48.6 -52.5 -52.4 -66.0 -64.7
-45.8 -52.8 -53.9 -63.3 -62.8

 

 

 

 

 

 

 

In order to study the effects of melt crystallization conditions on crystal
formation, all of the polymers were subjected to a heating scan after the samples were
annealed at a selected temperature for 30 minutes. The annealing temperatures were
chosen to be either just below or just after an endotherm detected in the DSC heating
scans taken after quenching. These results were compared with scans of samples stored
at room temperature, samples that had been flash quenched from the melt, and samples

that had been slowly cooled from the melt. Figures 52 to 56 are the data for polymers

133

 

(C31tC3EOy)n where y = 6, 7, 8, 10 and 14 respectively. For polymer (C31tC3E06)n
(Figure 52), we can see that it is amorphous at room temperature. As shown by the
shape and area under the endotherms, slow cooling resulted in better low melting crystals
(sharper endotherms) than did fast quenching. The highest temperature endotherm
showed no change due to annealing. Polymer (C31tC3E07).. (Figure 53) also is
amorphous at room temperature. The multiple peaks at 15-25 °C were barely visible in
the slow cooled sample, which is opposite to the previous sample. However, annealing at
0 °C enhanced these higher melting peaks. Annealing at higher temperatures further
increased the areas of the higher melting peaks. Polymer (C3TCC3E03)n (Figure 54) and
polymer (C31tC3EO7)n have similar behavior. No endotherms were seen for polymer
(C31tC3EOm)n (Figure 55) for the room temperature sample, even though the sample
appears to be somewhat crystalline. Recalling the morphology results in the previous
section that showed that this polymer is hard to crystallize, this result is not surprising.
That annealing the sample at 18 °C for 30 minutes did not yield any crystalline phase also
confirmed the difficulty in crystallization for this sample. Annealing also gave rise to
higher melting peaks for other DSC traces. DSC scans of polymer (C31CC3EOg)n (Figure
56) annealed at room temperature showed two endotherms at about 27 and 30 °C
respectively. Melt crystallized samples annealed under different conditions only yielded
the lower peak. However, increasing the annealing time at 20 °C did shift the endotherm
to higher temperature. The remaining polymers behaved similar to the already described
(C31IC3EOy)n series, and are not described here. Their DSC plots are included in the

appendix for reference.

134

 

heat flow, endo

 

 

 

(C375035014)n

’—
'—

 

‘ l

(Cancanio)n

 

 

l

j
J
J M

 

 

l

(CSRCSEO7)n

 

J‘

 

 

 

 

 

 

 

(031:0;wa l

-1 00 -50 50 1 00
temperature (°C)

 

 

 

Figure 48. DSC heating scans of polymer (CartCaEOy),, after flash
quenched from the melt.

135

 

heat flow, endo

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(C4TEC4EO14):— l

l
(C4RC4E010)n J l

l
(C41TC4E08),,JVL
(C4WC4EO7ln 1W
(C41tC4E05)n J

-1 00 -50 0 50

temperature (°C)

Figure 49. DSC heating scans of polymer (C41tC4EOy),, after flash
quenched from the melt.

100

 

heat flow, endo

 

(CBRCBEO14)n

 

 

(CBWC8E010)n

 

(CafiCaEOa)n

 

 

I

 

 

 

(Cancansln

 

 

 

 

 

(CsncaEOfin W
0 50

-100 -50
temperature (°C)

Figure 50. DSC heating scans of polymer (CBKCBEOY),, after flash
quenched from the melt.

137

100

 

heat flow, endo

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(Con095014)n J
(CQTCCQEot O)n Jl
(CgithEOB)n A
(CQTCCQEO7)n fl
(anC9E05)n
-100 -50 0 50 100

temperature (°C)

Figure 51. DSC heating scans of polymer (anCQEOy),, after flash

quenched from the melt.

138

 

/ k hold at 12 °c

 

hold at 6 °C

 

hold at 2 °C

 

 

hold at -5 °C

/\/\
/\/\
/\/\/\
M h... a. -1000
M
M

 

heat flow, endo

 

slow cooled

 

 

fast cooled

 

 

room temp. obtained

 

 

 

L l l l J l

 

-20 -1O 0 1O 20 3O 40 50
temperature (°C)

Figure 52. DSC heating scans of polymer (canC3E05)n with different crystallization
histories.

139

 

 

 

 

 

 

 

 

 

 

 

 

 

/\ hold at 18 °c
A /\/\ hold at 10 °c
‘8 M hOId at 0 00
C
(D
a“
2
iii
0
2
AR slow cooled
m fast cooled
room temp. obtained
F
-20 -10 0 1O 20 3O 40

temperature (°C)

Figure 53. DSC heating scans of polymer (canC3E07)n with different
crystallization histories.

140

 

 

 

 

 

 

 

 

 

 

 

 

 

/\ hold at 15 °C
hold at 5 °C
A
/\/\ hold at 0 °C
0
'O
C
G)
3'
.0
§
.: A slow cooled
A fast cooled
room temp. obtained
/
-20 -1 0 10 20 30 40

temperature (°C)

Figure 54. DSC heating scans of polymer (CancaE03)n with different

crystallization histories.

141

50

 

 

 

hold at 18 °C

 

 

 

 

/\ hold at 14 °c
A

A hold at 0 °C
0
'0
C
Q)
i
2
'5
(D
.C

A slow cooled

A fast cooled

 

 

 

room temp. obtained

 

/

 

15

25

temperature (°C)

35 45

Figure 55. DSC heating scans of polymer (canC3EO1o),, with different

crystallization histories.

142

 

 

f hold at 28 °C

 

hold at 20 00 for 16 hours J
/

 

 

 

 

 

 

 

 

hold at 17 °C
0
'O
C
(D
a“
2
2% hold at 0 °C
3 /
slow cooled
fast cooled

 

 

 

4

room temp. obtained

 

l

 

 

 

0 10

20 30 4O 50
temperature (°C)

Figure 56. DSC heating scans of polymer (C31t03EO14),, with different

crystallization histories.

The temperatures of the polymer melting transitions are summarized in Table 12.
If a sample gives a different Tm transition under different annealing conditions, the

highest transition temperature is also listed with a note of the crystallization conditions.

Table 12. Melting transition temperatures (°C) of polymers (anCxEoy)...

 

 

 

 

 

 

 

y
x 6 7 8 10 14
3 -3.8, 5.4, 4.6, 13.4, 6.6, 18.8 10.0, 16.5” 25.9, 30.7”
13.7 20.7
4 -20, 16.0, -7.5, 8.0, 12.9, 18.7, 12.7 24.5, 30.6”,
17.3” 13.0c 20.0d 31.9”
8 14.7, 36.7, 18.7, 30.8, 20.7, 23.2”, 19.3, 30.0” 30.7, 31.3”
40.0”, 42.1f 31.1” 31
9 7.3.33.3, 14.0, 28.3, 20.0, 24.1, 23.1, 31.1” 28.0, 30.6”,
37.3, 43.4” 28.7” 34.4, 36.3” 34.4‘3

 

 

 

 

 

 

a. annealed at 14 °C for 30 minutes. b. annealed at room temperature for long time.
c. annealed at 10 °C for 30 minutes. (1. annealed at 17 °C for 30 minutes. e. annealed
at 28 °C for 30 minutes. f. annealed at 40 °C for 30 minutes. g. annealed at 20 °C for

30 minutes.

In addition to DSC experiments, we used DMA to further establish the nature of
the thermal transitions seen in the DSC scans. Temperature sweep DMA can be used to
detect glass transitions, crystallization and melting transitions. It is more sensitive than
DSC for observing subtle transitions. The combined information of probe position,
storage (E’) and loss modulus (E”), and tan 5 (5 is the phase angle) can give a more

complete description of the nature of the transformation. However, the amount of sample

144

 

required for DMA is much larger than for DSC and the operation is more complicated.
Therefore, DMA experiments were performed only on a few samples. One example is
shown in Figure 57 together with the DSC heating scan for polymer (C41tC4EO3)... The
DMA sample was prepared by the same protocol used to obtain the DSC results, flash
quenching from 105 °C using liquid nitrogen. The initially amorphous sample was run in
a parallel plate geometry at a frequency of 1 Hz. Decreases in the probe position were
found at —50 °C and near —5 °C. The first transition correlates to an exothermic transition
in the DSC data and an increase in E’, and thus corresponds to the densification of the
sample during crystallization. The second transition, near —5 °C, is related to a decrease
in E’, an increase in tan 5, and an endothermic transition in the DSC data. During this
transition, the sample softens and the probe eventually penetrates through the sample, an

obvious indication of melting.

145

 

 

DSC L.

k

,J

Probe Position

 

\

 

 

 

 

 

 

-1 00 -80 -60 -40 -20 0 20

Temperature (°C)

Figure 57. DMA and DSC of polymer (C47rC4E03),, heating scans. The
bottom 3 traces are DMA results for a sample in a parallel plate geometry.

146

5. XRD of unsaturated polymers

The polymer (CottCoEO7).l was characterized by XRD experiments. Data for
samples crystallized from hexane, methanol and the melt respectively are shown in
Figures 58 (low angles) and 59 (high angles). Since it is hard to obtain well crystallized
polymer samples, the XRD scans do not have an ideal signal/noise ratio. However, from
low angle XRD one can see that the highest ordered peaks appear almost at the same
position, corresponding to a d-spacing approximately 42.4 A. In the higher angle region,
samples crystallized from hexane showed a slight difference from the other two. The
peak at 195° is absent in the other two samples and the intensity ratios at 22-27° are also

different.

An attempt was made to correlate the multiple transitions in DSC heating scans to
polymer structure. XRD data were taken for polymer (CxtthEOy)u at different
temperatures. The polymer sample was first melt-quenched to liquid nitrogen
temperature, and then heated to temperatures just below or past the transition point
indicated in the DSC scan (Figure 60). XRD were taken at those temperatures and their
profiles are shown in Figure 61. At —80 °C, below the polymer’s T8, the sample
appeared to be amorphous and only a halo at around 20° was visible. As the temperature
increased to above Tg, where chain segments were able to move and rearrange into a
more ordered structure, diffraction peaks start to emerge. Peaks at low angles were
barely seen until —15 °C. At that temperature, after the second crystallization exotherm, a
broad diffraction at around 3.7° was seen that persisted until the sample was melted.
Presumably an ordered structure with a long spacing formed. In the high angle region, a

major peak at 228° first emerged with another smaller peak at 194° at just above Tg. As

147

the peak at 194° became sharper and better defined, it also shifted slightly to a lower
angle. The sample crystallinity was finally lost as the temperature increased to above the
melting points. All peaks disappeared except for the halo around 20°. Interestingly, its
peak position was shifted to a lower angle than the original halo position. Partial analysis

of the results appears in the Discussion section.

148

intensity

 

 

from melt

 

29

Figure 58. Low angle XRD of polymer (CgitcgEoy),, sample

prepared using different crystallization conditions

149

from methanol
5 I ,1"? l .
. ,3 111‘ from hexanes
1 { {Vii/‘1‘“
r. If" 3‘“: ’ fling. :VRU’. , IIJflJK'I‘izf‘.)l 9:1 . ”if; ’1?
1 T l l T
1 2 3 4 5 6

 

intensity

 

 

from melt

from methanol

from hexanes

 

 

 

 

15 20 25
2 9

Figure 59. Wide angle XRD of polymer (anC9E07),, samples
prepared using different crystallization conditions

150

5952.55 995 9:95.098 omx 99:5 59399.89 95 9552 9592
9.9: 95 :85 55:96 :96: :98 5.506 or am 9508 5:6 9:59.. cAmOmvoaoov 9:29. 8 Own. .oo 0.52“.

AOOV 929959

 

 

 

 

 

 

 

 

     

 

 

 

9» ON 0 ON- ov. om- om- oo 7
tr . p — _ p F ON
T om
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> w
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if 9
W
l 0
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OOVF Oom- Oom _.1 0o Fm”: 000m: Comm: OoOwl
OomFI 0005.. r ON

 

 

 

cm

151

intesity

 

 

 

 

 

 

 

 

 

 

 

l l

 

2 1 2 22 32

29

Figure 61. XRD of polymer (C47IC4E05),, as a function of temperature

152

 

IV. Properties of saturated (AB)n polymers (CxEOy)In
1. Physical properties

The molecular weights and polydispersities of the hydrogenated polymers are
given in Table 13 together with their corresponding unsaturated precursors. As can be
observed in the table, their molecular weights all dropped after hydrogenation. The
saturated polymers are white, presumably because most of the residue catalyst was
removed during the reaction and the work-up procedure. Since the polarity of the
saturated polymers is not significantly altered by hydrogenation, they exhibit the same
solubility trends seen for the unsaturated polymers. Both saturated and unsaturated

polymer can absorb moisture, therefore they must be kept in a desiccator.

153

Table 13. Comparison of the molecular weights and polydispersities of the

hydrogenated polymers (C2,,+2E0y)n and their unsaturated precursors (anCxEO,)n.

 

 

 

 

 

 

 

 

 

Unsaturated polymer Saturated polymer

polymer Mn PDI polymer Mn PDI Yield
(C47IC4E06)6 48,800 1.84 (C 1 0EO6),, 1 1,800 1.64 97%
(C41tC4EO7).. 25,100 2.27 (C I 0EO7),, 15,800 1.85 98%
(C4KC4E08)6 19,400 1 .41 (C 1 oEOg)n 13,200 1.98 98%
(C4RC4E010)n 28,300 2.01 (CloEOm)n 24,100 2.41 99%
(C411C4EOM)n 13,200 1.81 (C IOEOM)" 8,500 1.58 99%
(91:51:07)“ 11,800 1.44 (C20E07)n 9,500 1.45 99%

 

 

 

 

 

 

 

2. Morphology of saturated polymers

All of the saturated polymers are crystalline at room temperature. Crystals
obtained by crystallization at room temperature for at least 3 weeks were viewed using

cross-polarized optical microscopy.

Shown in Figure 62 are crystals of (C10E06)n and (CmEO-l)n viewed under
polarized light. Crystals from these two samples are banded spherulites, but unlike the
unsaturated polymers, the bandwidths are not uniform for all spherulites. In addition, the

bands were not always concentric. For example, in the (C10E06)n sample, the bandwidth

154

 

on the front spherulite is about half of that of the background spherulite. Furthermore,
spherulite bandwidths can increase with annealing time (at room temperature). This can
be clearly seen in Figure 63, for a crystalline sample of polymer (C10E07)n. Crystals
originally formed at room temperature have mainly small hands like that in the lower
middle section of the picture. After being stored for a while, they gradually grew into
large spherulites with larger bandwidths. The reasons behind this phenomenon needs
further study. One possibility could be unfolding of polymer chains to form more

extended chains, which results in lamellar thickening.

The remaining micrographs shown in Figure 64 are for polymers (C10E03)n,
(C10E010)n, (C10E014)., and (C20E07)... These crystals were ordinary spherulites except
for (C10E010)n, whose spherulites show obvious light extinction at the center. The
crystals that constructing the spherulites were also more sheaf-like comparing to the other

crystalline samples.

155

 

Figure 62. Micrographs of polymers (C10E06)n (left) and (C10EO7)n (right) under cross-
polarized light

 

Figure 63. Micrograph of polymer (CmEO7).1 under cross-polarized light showing
different band widths.

156

.9 ¢ .14
t. ‘rxcfix 5W»

 

(upper right).

Figure 64. Micrographs of polymers (C10E03)n (upper left), (C10E010).,

—polarized light.

and (C20E07)n (lower right) under cross

(CmEOML, (lower left)

157

3. Thermal behavior of the saturated polymers

The saturated polymers were also analyzed by DSC. The sample preparation and
experiment methods were the same as for the unsaturated polymers. Shown in Figure 65
are the DSC heating scans taken after flash quenching polymers (CmEOy)u where y = 6,
7, 8, 10 and 14 respectively. All of the polymers show Tgs at low temperature. Except
for polymer (C10E014)n, which showed only one endotherm, all of the polymers show a
melting—crystallization—melting sequence. When the ethylene oxide segments become
longer, the low temperature melting transition becomes more prominent for polymers
with y = 7, 8 and 10, indicating that the low melting structures favor long ethylene oxide
segments. The Tgs and melting transition temperatures for samples crystallized after

quenching and for samples annealed at room temperature are shown in Table 14.

In order to study the effects of melt crystallization conditions on crystal
formation, all of the saturated polymers were annealed and their DSC scans were taken in
the same way as for the unsaturated polymers. Figures 66 to 70 show the DSC heating
scans for polymers (CloEOy)n where y = 6, 7, 8, 10 and 14 respectively. For all saturated
polymers, samples stored at room temperature have the highest melting points among all
the crystallization histories. For polymer (C10E06)n (Figure 66), the DSC traces looks
similar for both quenched and slow cooled samples. However, annealing the quenched
sample at 3°C shifted the lower melting peak to an even lower temperature, which
appears abnormal at first glance. Moreover, similar phenomena were observed for
polymer (C10E07)., (Figure 67). The DSC heating trace taken after slow cooling shows
3 endotherms but only 2 after quenching. After annealing at 0 °C, the second endotherm

seen in the DSC scan of the slow cooled sample disappeared while the first endotherm

158

grew. This phenomenon will be discussed later. When crystallized and annealed at room
temperature, polymer (C10E014)n (Figure 70) showed two overlapping endotherms
indicating that two kinds of structures exist at room temperature. Flash quenching and
slow cooling both gave a lower melting crystal than the two crystals formed after long
term room temperature annealing. Annealing at 20 °C for 30 minutes increased the
melting point, and annealing at 30 °C for 30 minutes gave a mixture of crystals, those
obtained from short time annealing at 20 °C and one of the low melting crystalline forms
seen for long term room temperature annealing. Finally, annealing at 33 °C gave mainly
the highest melting crystal. The thermal behavior of polymers (C10E03)n and (CmEOm)n

was not surprising.

Table 14. Tg and Tms of saturated polymers. (°C)

 

 

 

 

 

 

 

 

Polymer Tg Tm
(C10E05)n -78.7 11.2, 21.8, 22.63
(C10E07)n ~63.1 6.8, 22.2, 25.0al
(C10E08)n -64.9 2.5, 19.6, 23.1a
(C10E010)n -65.9 14.6, 25.3, 28.4a
(C10E014)n -63.7 24.3, 26.6, 37.48
(C20E07)n -52.9 11.1, 28.9, 44.7, 45.7a

 

 

 

a. annealed at room temperature for more than 2 weeks

159

 

 

heat flow, endo

 

 

 

 

 

(010E014)n

 

(C1OEO10),,

 

(C10E08)n

 

 

 

J
J

(C1OEO7)n

 

 

 

(C10E06)n

 

 

 

 

 

0
temperature (°C)

50

100

Figure 65. DSC heating scans of polymers (C10E0y),, after flash

quenching.

160

 

 

 

 

 

 

 

 

 

 

/\ hold at 15 °C
0
'2 slow cooled
d)
a“
..-‘=’
‘6
a)
.C
M fast cooled
room temperature obtained

 

20 3O

tempearture (°C)

40 50

Figure 66. DSC heating scans of polymer (C1,,E05)n with different

crystallization histories.

161

 

hold at 18 °C

 

hold at 10 °C

 

 

 

slow cooled

heat flow, endo

 

A
fl
M

fast cooled

 

room temperature obtained

 

 

 

1 1 1 1

0 1 O 20 30 40 50
tempearture (°C)

Figure 67. DSC heating scans of polymer (C10EO7),, with different
crystallization histories.

162

 

 

hold at 18 °C

 

hold at 8 °C

M hold at -5 °C _
fast cooled

room temperature obtained

 

 

heat flow, endo _____,

 

 

 

v—f

 

 

l l

 

T T

-5 5 1 5 25 35 45
temperature (°C)

Figure 68. DSC heating scans of polymer (C10E03).. with different
crystallization histories.

163

 

 

 

 

 

 

 

 

 

 

hold at 25 °C
A
hold at 10 °C
0
'O
C
d)
3'
O
E J\/\ slow cooled
<13
m
.C
4” fast cooled
room temp. obtained
0 10 20 30 4O 50

temperature (°C)

Figure 69. DSC heating scans of polymer (C10EO10),, with different

crystallization histories.

164

 

heat flow, endo

 

 

/\

i
J
J

J

hold at 33 °C

 

hold at 30 °C

 

hold at 20 °C

 

slow cooled

fast cooled

 

room temp. obtained

 

 

 

temperature 0(°C)

60

Figure 70. DSC heating scans of polymer (C10EO14),, with different

crystallization histories.

165

 

4. Spectroscopic characterization

The most prominent change for a saturated polymer compared to its precursor is
the removal of the double bonds. This was clearly seen from spectroscopic
characterization. For example, in lH NMR, the peaks at 5.4 ppm, which correspond to
the internal double bonds, gradually diminish during the hydrogenation process. Other
than this change and some minor shifts of the protons on the carbons adjacent to the
original sp2 carbons, the spectrum looks similar to that of the unsaturated polymer.
Disappearance of bands that correspond to double bond vibrations were also sighted in IR

and Raman spectra.

IR spectroscopy was again used to study the polymer conformations. Polymer
(CmEO-I)“ was crystallized from hexanes and methanol, as previously done for the
C14EO7C14 sample. As shown in Figure 71 (only the low frequency region is shown),
the spectra are quite different which indicates that different conformations or crystal
packing exist in the polymer chains as crystallized from different solutions. The details

will be discussed later.

166

 

MN!”

 

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i

f

we"

 

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a :
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\lex l

. fps
Rye
Kayne}

from hexanes

"V

 

 

 

 

I

1 400

1 200

l T

1 000 800

wavenumber (cm")

600

Figure 71. IR spectra of polymer (020E07),, crystallized with different

solvents

167

5. XRD results for saturated polymers

We attempted to obtain XRD results for saturated polymers (CxEOy)n, however,
due to the limited amount of saturated polymer samples available with y 2 6, we were
unable to obtain spectra for these polymers with reasonable signal/noise ratios. These

samples will be tested once larger quantity of sample are available.

As was attempted for the unsaturated polymers, we tried to correlate the DSC
transitions of the saturated polymer (CmEOs)n with the polymer structure. The sample
was treated in the same way as described for the unsaturated polymer. The temperatures
where XRD data were taken are shown in the DSC curves of this sample in Figure 72.
The XRD profiles are shown in Figure 73. It is seen that even for fast quenching in
liquid nitrogen, some crystalline material formed as indicated by a sharp peak at about
20° and several small peaks on top of the amorphous halo. This implies that the saturated
polymers are very easy to crystallize. Heating the polymer to -25 °C, which is above the
polymer Tg, initiated additional crystallization. A new peak emerged at 24 °C and
became better defined as the sample was heated to 12 °C. After passing the first
endotherm, peaks appeared at 21.7° and 221° 26 values. These peaks disappeared after
the polymer was heated past the second DSC endotherm. All of the diffraction
disappeared once the polymer was melted. When the polymer was cooled to below its
crystallization temperature, the sample diffracted again. However, although the pattern
persisted, all of the peaks were shifted to higher angles. Further discussion is included in

Discussion section.

168

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intesity

 

 

l

 

 

 

 

[\N
at -77 DC A ‘ h
at -25 °C Ii
at 12 °C - m |

 

 

cooled to 0 °C

 

 

 

cooled to -130 °C J

——.——

 

 

l T l

12 22 32
2 6

Figure 73. XRD of polymer (C10E05),, as a function of temperature.

Note: peaks at 31 .7° 26 are diffraction from NaCI impurity.

170

DISCUSSION

1. Synthesis and Purification
1. Synthesis of exact length ethylene glycols

Because the physical properties of the block copolymers are sensitive to
distributions in the lengths of the blocks, compounds where the length of each block was
exact needed to be prepared. Exact length alkyl or alkenyl segments are readily
available, and thus the main synthetic challenge is obtaining the exact-length PEGs
needed for the desired ABA structures. PEGs are commercially available in a variety of
molecular weights, but only a limited number of exact-length glycols are available in
high purity. Chromatographic separation of glycols from commercially available PEG
mixtures was considered, but to ensure the purity of the glycols in the amounts needed
(tens of grams), we opted for an iterative synthetic approach that allowed us to access a
broad range of PEG lengths on large scales. With the increased interest in using PEGs in
polymer-supported solid phase synthesis, cyclic ethers, and as elements of new materials,

there have been several reports describing the synthesis of exact length PEGs. We
adopted a modified version of the approach of Keegstra et (11.165 to prepare glycols

where y is 6-10 and 14. The route to these PEGs is outlined in Scheme 22.

Success in any iterative synthesis demands that each step proceeds in high yield
and that each intermediate be readily purified. Our work incorporated modified work-up

protocols designed to simplify product isolation and minimize the need for chlorinated

171

solvents. For the preparation of the ditosylates, we used aqueous KOH instead of the
powdered KOH/CH2C12 mixture used by Keegstra. KOH and TsCl have limited
solubility in CHzClz and therefore the KOH needed to be powdered and the reaction
concentration can not be very high. By switching to a THF/water solvent system, the
solubility of all the reactants was greatly enhanced. In addition, ditosylate products are
insoluble or poorly soluble in water, and therefore were excluded from aqueous phase
and helped drive the equilibrium toward the products. In our hands we found that the
aqueous system gave purer products in higher yield. Furthermore, we noted that the

conditions used by Keegstra (dry CHzClleOH) are very similar to those used for

preparing chain extended polyethylene oxide polymers.167 By switching to an aqueous

system, we also eliminated chain extension as a potential side reaction.

The work-up procedure for the monotritylates was also simplified, enabling us to
obtain pure products in high yield. Both the monotritylate and ditritylate syntheses were
modified to eliminate the need for CHzClz. Water played an important role in the
modification. Previously, because it was thought that water might reduce the reaction
yield, water was strictly excluded from the reaction and during the work-up. We, on the
other hand, found that the monotritylates are almost insoluble in water, and the excess
reactant (ethylene glycol) and pyridinium hydrochloride, are very soluble in water.
Therefore, water was used to precipitate the monotritylates from the glycol solution and

then was used in the washing procedures.

In the deprotection reaction, the H3 pressure was increased to 50 atm from 5

atm165 to drive the reaction to completion in a shorter time. Washing the methanol

solution of oligoethylene glycol with hexanes also facilitated the removal of trace

172

amounts of the triphenyl methane byproduct. With these modifications, the overall yield
of most of the five step syntheses can be 2 90%, enabling us to obtain sufficient amounts

of exact length PEGs.
2. Monomer purification

Since Schrock’s molybdenum catalyst is very sensitive to impurities such as
water, oxidants and chelating functional groups, the monomers for ADMET need to be

very pure. Both the polymerizability and polymer molecular weight depend greatly on

monomer purity.78’79

Of the anEOyCm: monomers we synthesized, only the low molecular weight
monomers can be purified by vacuum distillation. When y 2 6, the boiling points of the
monomers are too high for distillation. We developed a new method to purify monomers
in this category. First, we used column chromatography to separate the monomer to >
95% purity. The remaining impurities were believed to be trace amounts of water,
alcohol and a side product that seems to contain an aldehyde. All of these can react with
sodium metal to give salts. However, only freshly exposed sodium metal can react with
them. We borrowed the purification method used to purify solvents for anionic
polymerization—the use of sodium mirrors. The fresh sodium surface was formed by
vacuum sublimation of a small chunk of the metal to form a mirror-like coating on inner
surface of the flask. The impurities react with the fresh sodium surface and eventually
are converted to a salt. In the conventional purification scheme, the sodium mirror
purification is followed by distillation, which is not applicable for y 2 6. We considered

an altemative—filtration. Since the salt particles formed are small and the ethylene oxide

173

segments of the monomer can solublize salts well, a competitive substrate needs to be
provided to absorb them. Because the impurities after the purification reactions exist as
anions, an acid is required, preferably a weak acid that can be easily separated from the
monomer. A solid phase weak acid would be an ideal candidate, and acidic alumina
satisfied all the requirements. In order to reduce excess absorption of the monomers and
the passage of small particles passing through the filter pad, the alumina was mixed with
Celite® in a 1:5 ratio. This material was packed in the middle of a small column flanked
by pure Celite® on both ends to further prevent leakage of small salt particles through the

filter, and the packing materials from being stirred by the solution stream (Figure 10).

This method was a key step in obtaining high purity monomers for this project,

and greatly expanded the scope of pure monomers available for ADMET polymerization.
3. Polarity changes of the compounds in this research

The building blocks of the copolymers in this research can be viewed as analogs
of polyethylene and polyethylene oxide. These two building blocks have opposite
polarities. Polyethylene is hydrophobic and soluble in non-polar organic solvents, while
polyethylene oxide is hydrophilic and soluble in most polar solvents including water. By
connecting these two kinds of blocks in one molecule, it is expected their polarities

should show systematic changes based on the volume fractions of the two blocks in the

copolymer.
The solubility parameter is defined as in equation 154

a: (Ali/V)”2 eq. 15

174

where AE is the energy of vaporization to a gas at zero pressure (i.e., at infinite separation
of the molecules), and V is the molar volume of the material. The quantity AE/V is the
energy of vaporization per cm3. This term is sometimes called the cohesive energy
density. Based on the simplest notion about solubility “like dissolves like”, polymers or
oligomers will dissolve in solvents that have similar 6 values.

The solubility parameter for a polymer structure may be calculated using

1/2
1

empirical group attraction constants, G (ca cmmmol'l), for each group.

5=— eq.16

where p (g/cm3) represents the density and M (g/mol) is the repeat unit molecular weight.

We made a simple estimate of the solubility parameters of the unsaturated
polymers synthesized for this project based on the known values for polyethylene and
polyethylene oxide. For a specific polymer, the formula (CxtthEOy)n indicates it
consists of a (CH2CH2)x segment, a (CH=CH) segment, a (OCH2CH2)y segment and one
O atom. The G values of (CH=CH) and the O atom are 222 and 70 respectively (units
omitted). 168 Giving the solubility parameter and density values of polyethylene (7.9 and
0.85 respectivelyl69) and polyethylene oxide (9.9 and 1.20 respectively169), the C
values of (CHzCHz)x and (OCH2CH2)y were calculated to be 260 and 363 respectively.

Therefore,
21? = 260x + 363y + 222 +70 eq. 17

Meanwhile, the repeat unit molecular weight can be calculated from the polymer

formula and the polymer density can be estimated based on the density of PE and PEO

175

and the component weight fractions. As a rough estimate the density of the alkenyl
segment was taken the same as that of PE. The polymer density estimation is now

written as:

Ppozymer = ,DPEOWPEO +13%“ ‘WPE0) eq. 18
where WPEO is the weight fraction of PEO segment in the polymer.

Using the known values, the solubility parameters 8 were calculated and are
shown in Table 15 and plotted in Figure 74. From the figure, we can see that the
solubility parameter increases as the ethylene oxide fraction increases. Also when the
alkenyl fraction increases, the solubility parameter drops. Solubility parameters of some

common solvents are given in the figure for comparison.

This systematic change in solubility parameters explains the requirement for a
series of solvent adjustments needed for monomer and polymer purification. For
example, all of the polymers have solubility parameters between 8.3 and 9.5 (cal/cm3)”2,
explaining why toluene ((5 = 8.9) can be used to dissolve all of the polymers. Hexanes,
with 6 close to 6.6 (cal/cm3)”2, can be used to precipitate all the polymers. Meanwhile,
only polymers with long alkenyl and short ethylene oxide segments can be precipitated in
alcohols. The values of the calculated solubility parameters can be used as a guideline
for choosing the solvent for purification and further manipulations of the polymers.
However, when each segment is long enough, this 5 model, based on the averaging the
effects of the two types of blocks, breaks down. At some block length, phase separation

is strong enough so that the blocks will act independently. This prediction was proved by

the solubility of polymer (C31tC3E014)n in water, whose calculated 5 value, 9.52, is 13.9

176

smaller than the 5 of water (23.4). The solubility is presumably due to the formation of
micelle-like structures in water, which is also observed in a preliminary result in some
triblock oligomers.

“2

Table 15. Solubility parameters 8 [(cal/cm3) ] of unsaturated polymers

(C,nc,Eo,),,.

 

 

 

3 8.57 8.80 8.96 9.08 9.18 9.25 9.31 9.40 9.52

 

4 8.51 8.73 8.89 9.01 9.11 9.18 9.25 9.34 9.47

 

8 8.34 8.52 8.67 8.79 8.88 8.96 9.04 9.15 9.30

 

 

9 8.31 8.49 8.63 8.74 8.84 8.92 8.99 9.11 9.27

 

 

 

 

 

 

 

 

 

 

177

 

 

9.6

 

 

 

 

 

 

 

 

Methanol 8 = 14.5
Acetone 8 = 9.9
9 4 _ Toluene 6 = 8.9
' n-decane 5 = 6.6
9.2 .
"E
g
:3, 9 «
DO
5
‘6
E
S
3 8.8 —
.5
L5
_:_
O
U)
8.6 «
I
8.4 - +3
+4
+8
+9
8.2 , 1
O 5 10

number of EO units, x

Figure 74. Estimated solubility parameters of unsaturated polymers

(anCxEOy),,. Numbers in the inset are x values.

178

15

4. Polymerization details
Polymerizability of monomers

Polymers were successfully synthesized from all the monomers made in this
research except for the nCzEOyCzn series of monomers. The monomers in this series
were contaminated by the allylic isomerization of the terminal double bonds as shown in
Scheme 28. Since the properties of these compounds are so similar, isolation of pure
nConyCzrt monomers was almost impossible. Double bonds allylic to the oxygen
atoms are thought to form a stable adduct during polymerization as shown in structure
23.170471 The oxygen atom chelates to the Mo atom and blocks the site for further
reaction, thus leading to poisoning of the catalyst. The possibility of forming a cyclic
product via ring closing metathesis was also proposed for some numbers of the
nCzEOyCztt series.166 However, since the problems persist for all of the monomers in
the series, this hypothesis seems unlikely to be correct. We believe the chelating effect of

the oxygen is the main reason for the failure of the polymerization in this series.

Molecular weight related factors

ADMET polymerization is a step growth polymerization. It has been shown166
for the polymerization of this family of ethylene oxide segmented polymers, that the

molecular weights increase with their degree of polymerization, Xn as
Xn = 1/(1-p) eq. 19

where p is the fractional conversion of the terminal vinyl groups to internal double bonds.

179

Scheme 28. Isomerization of nCzEOyCztt double bonds

WOWO/W

isomerization

WOWOM or WOWO/W

/
.MQW

23

Scheme 29. Back-biting for polymer degradation

LnMO LnMO

F

/

LnMo

180

The polymerization reaction competes with side reactions that can either

terminate the reaction, such as catalyst degradation, or lower the molecular weight, such

as “back biting”. Schrock’s molybdenum catalyst is unstable above 60 °C.64 When
polymerizing monomers in the bulk state, the reaction has to be run at 50 °C to melt the
monomers, but at this temperature, the catalyst slowly decomposes which leads to a
decrease in polymerization rate in addition to that caused by the reduction in the
concentration of the terminal double bonds. Occasional additions of small amounts of

catalyst were used to solve this problem for long reaction times.

The back biting reaction is shown in Scheme 29, where the propagating
intermediate attacks a double bond in its own chain instead of reacting with the terminal
double bond of another molecule to extend the polymer chain. The result of this reaction
is a new linear reactive intermediate and a macrocyclic ring. This side reaction is more
favored when the reaction system is dilute, since the chance of a reactive site meeting
another molecule to extend the chain is less than that of finding another double bond in
its own molecule. This phenomenon was best observed for high molecular weight
polymers. Diluting the polymerization with solvent always resulted in reduction of the
molecular weight. On the other hand, when the polymerization system is too viscous, the
reaction rate is low since it is diffusion controlled. To increase the diffusion rate, the
viscosity was decreased by both increasing the temperature (which can only be raised to
50 °C) and addition of solvent. According to our experience, adding one 15 mL portion
of toluene to a 5 g scale reaction after the bulk polymerization stage always gave good

results.

181

Saturated polymer molecular weight

When the unsaturated polymers were reduced to saturated polymers, their
molecular weight dropped substantially (see Table 13). This phenomenon was observed
for both catalytic hydrogenation and reactions using tosylhydrazine (TsNHNHz).
Previously, the molecular weight decline was suspected to be an artifact of the GPC

measurement. It was proposed that the hydrodynamic radii of the saturated polymers

might be smaller than for the unsaturated polymers.166 Since GPC is a relative method
that measures the molecular weight by measuring the particle size, it is possible to obtain
higher than expected molecular weight values if the polymer is highly swollen.
However, when we used membrane osmometry, which gives absolute molecular weights,
we found a similar molecular weight drop. This confirmed that degradation occurred

during the reduction of the unsaturated polymer.

Given the high salt affinity of the PEO segments, trace amounts of catalyst
residues were always present in the purified polymers, and the polymers appeared to be
colored as a result. However, the saturated polymers were always white solids
immediately after hydrogenation. If stored in air for more than several days, the white
color reverted to almost the same color as their unsaturated precursors. We terminated
the catalytic hydrogenation before the unsaturated polymers were completely reduced.
These samples were colorless after work-up. We believe that the residual catalyst was
reduced during hydrogenation to give a colorless oxidative state for molybdenum. If
molybdenum is in a lower oxidative state, it probably played a role in degrading the
polymers to lower molecular weight. Further experiments are needed to fully elucidate

the problem.

182

11. Structure and properties of triblock oligomers

In our triblock oligomers, which also serve as model compounds for our (AB)n
microblock copolymers, we incorporate exact length segments of polyethylene (A) and
polyethylene oxide (B) into the oligomers in a ABA pattern. The PEO and PE segments
strongly phase separate and unlike most block copolymers, both segments crystallize to
form a rich variety of crystalline phases. One particularly interesting feature of PE/PEO
microblock polymers is that the PE and PEO blocks normally adopt strikingly different
crystal structures. PE typically crystallizes in an orthorhombic unit cell with the chains

aligned along the c-axis in a planar zigzag conformation while PEO crystallizes as a 72
helix,97 although a stress-induced metastable phase which contains planar zig-zag chains

has been reported. 109,1 10 By chemically connecting these blocks into one molecule, we

observed a variety of structures in the ABA oligomers.
1. ABA oligomers CxEOny with y S 6

Since the A and B segments adopt different structures in their homopolymers,
they will have to compete to get the best structure in the same molecule. The PE
segments have a single link to the PEO segment, and their conformation should be the
ordinary planar zigzag conformation. This can be inferred from the 718 cm"l band in IR
spectra, a CH2 rocking vibration with a planar zigzag packing. The PEO segment is
flanked by two PE segments, and thus it is not easy for it to adopt its preferred helical
conformation. All triblocks show similar behavior in the IR (Figure 37), XRD (Figure
29, 30) and DSC (Figure 22) and therefore we believe they have similar solid state
structures. We chose a representative oligomer, C15EO3C16, to further investigate the

molecular structure. Powder XRD showed that this compound crystallized to form a

183

lamellar structure as evidenced by the well-defined series of 001 peaks. We calculated
the molecule’s end to end distance using a molecular mechanics routine considering two
different PEO conformations. As shown in Figure 75, the oligomer with PEO in a
helical conformation gives an end to end distance of 47.2 A, compared to 51.1 A for a
planar zigzag conformation. Comparing the calculated results with the 51.3 A layer d-
spacing from powder XRD indicates that the structure of triblock C1¢E03C16 has fully
extended chains oriented normal to the layers with the ethylene oxide core in a planar

zigzag conformation as illustrated in Figure 76.
2. ABA oligomers CXEOyC, with y = 7
Crystallization of oligomers from solvent

Samples with 7 ethylene oxide units were the most interesting since XRD (Figure
29 and 30) and DSC data (Figure 22) depend on sample history. We first focus on the
structures of solvent crystallized C14EO7C14. This sample has a melting point of 41 °C
when crystallized from methanol, but melts at 39 °C when crystallized from hexane
(Figure 22). The XRD results however, show that these two samples have distinctly
different packing arrangements in the solid state. For the sample crystallized from
methanol, the XRD results give a layer spacing of 60.1 A, while the corresponding value
for samples crystallized from hexanes is 52.7 A. Thus, layered crystals of comparable
stability are formed but the individual molecules in the layers have different

conformations.

184

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Figure 76. Triblock oligomer C16E03Cm with lamellar structure.

 

from hexane

from methanol

 

 

 

 

 

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The nature of the difference between the two structures can be seen in Figure 77.
Shown are the Raman spectra for samples crystallized from hexanes and methanol
compared with a regular PEO sample and a PEO sample under tension. The sample
crystallized from methanol has bands at 1498 (CH2 bending), 1150 (CH2 rocking) and
1041 cm'1 (CC stretching), a pattern that is identical to that of highly oriented PEO held

under tension. Such samples have been shown by x—ray diffraction to have a planar

zigzag backbone conforrnation.109,110 The spectra also match the data from a
C14E03C24 oligomer that has a planar zigzag conformation. Thus the chain conformation
for samples crystallized from methanol must be the fully extended trans conformation
shown in at the top of Figure 78. The same conclusion is reached from an analysis of the
IR data (Figure 37). Meanwhile, the d-spacing measured for this sample (60.1 A) agrees
well with the calculated molecular end to end distance (60.4 A) in a fully extended

conformation.

To assign the chain conformation of samples crystallized from hexanes, we again
focused on the Raman and IR data. The spectra show the bands characteristic of helical
PEO (Figure 77), and the structure that best fits the data has a PEO core axis with the
conformation of a 72 helix flanked by alkyl groups in their usual planar zigzag
conformation (evidenced by the 718 cm”1 IR band). The calculated length of the linear
structure is larger than the layer spacing observed by XRD, but by tilting the alkyl chains
21° relative to the PEO core (see bottom structure in Figure 78), the overall length fits

the layer spacing, and provides more efficient packing for the alkyl groups. Similar
conformations also have been proposed for AB nonionic surfactant5128’13la132 and for

a series of ABA oligomers where m = 9.1362138

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Solvent crystallization mechanism

To understand why we obtain either a helical or a trans conformation for the PEO
core under different crystallization conditions, it is reasonable to consider a step—wise
process for the crystallization of the ABA oligomers. In particular, we believe that given
the amphiphilic nature of the oligomers, the A and B sub-units pre-organize before
crystallization. Thus the outcome of the crystallization process should be governed by
the relative solubilities of the A and B segments in a given solvent. As shown in Figure
79, in hydrophobic solvents the alkyl portions of the oligomers should be more soluble
than the PEO core, and the less soluble PEO core should crystallize first and choose its
most stable conformation, the 72 helix. When the alkyl fragments crystallize, they adopt
their normal planar zigzag conformation, but tilt with respect to the PEO core axis to
accommodate the helical structure of the PEO core and to increase the packing density.
This situation should be reversed when hydrophilic solvents are used for crystallization.
For example, crystallization from methanol should yield a pre-organized structure where
the alkyl portions are poorly solubilized. Thus the alkyl portions of the oligomers should
crystallize first in a trans zigzag conformation. When the PEO segments crystallize, they
must conform to the structure defined by the alkyl segments and thus adopt a trans
conformation. We note that this mechanism is not unlike that of protein folding, where

the hydrophobic residues associate and help define the structure of the protein.

Even though spectral data show that ABA oligomers with PEO cores shorter than
7 repeat units all have planar zigzag conformations, the abrupt formation of a helical unit
in these oligomers at m = 7 should not be surprising. To insert a stable helix into a

polyethylene chain and retain high crystallinity requires that the junctions between the

191

PEO and PE chains have similar symmetries, a condition satisfied when the length of the
PEO helix corresponds to one unit cell. This result points to a general strategy for
incorporating stable crystalline polymer sub-units into materials. By using segment
lengths that correspond to multiples of the polymer unit cell, such segments can be
expected to self-assemble into crystalline sub-units that have the same structure as the

parent polymer.
Melt crystallization of oligomers

When the oligomer C14EO7C14 was crystallized from melt, it also gave different
crystal structures depending on the crystallization conditions. The powder XRD results
of a flash quenched sample which had been held at above its melting point for an
extended time showed that the d-spacing is 54.6 A (Figure 31). Annealing this sample at
room temperature showed that its d-spacing gradually shifted to a higher value (Figure
31) within hours. The majority of the resulting crystal has a d—spacing corresponding to
that of a fully extended conformation. If the sample was annealed at a higher temperature
the conversion was faster. Figure 35 shows that the crystal with the shorter d-spacing
was mostly converted to that of the extended form within 14 minutes at the annealing
temperature of 35 °C. Similar conversions at 35°C were also seen in DSC experiments
(Figure 21). These transformations were also noticeable in the wide angle XRD profiles
(Figure 32), where the profile for the initially obtained crystal is very different from that
after annealing. The wide angle XRD of the annealed sample resembles that of samples
crystallized from methanol. Raman spectroscopy experiments showed the conformation
changes of the PEO segment in this sample. With time, the melt quenched sample which

had a helical PEO core, was converted to a planar zigzag conformation as evidenced from

192

bands emerging at 1498, 1150 and 1062 cm". The oligomer C14EO7C14 was also
isothermally crystallized at equilibrium temperature since this should yield the most
thermodynamically stable structure. The powder XRD of this sample showed a d-
spacing corresponding to the fully extended molecular conformation, and this d-spacing
did not change with time (Figure 33). The wide angle XRD of this sample (Figure 34)

also looks very similar to that obtained from the sample crystallized from methanol.

From the information given above, we can infer that the melt quenched crystal has
a helical PEO core and a planar zigzag alkyl chain. The structure is very similar to that
obtained from hexane, but since the d-spacing is shorter, the alkyl chain tilt angle with
respect to the PEO helix axis should be smaller. We estimate it to be about 10°. This
conformation is not stable at room temperature and slowly transforms to the fully

extended molecular conformation.

More interestingly, these samples seem to show a memory effect with respect to
its conformations. When a planar zigzag sample was melted and then quenched to
recrystallize the sample, the crystal form obtained was decided by the time the sample
was held in the melt state. For short times, the crystal obtained had more planar zigzag
molecules than helical PEO molecules. Longer holding times gave opposite results. If
the sample was held at melt long enough, the quenched sample contained no extended
molecules; all of the sample was converted to molecules with helical PEO cores. These
differences can be quantified from DSC experiments by measuring the relative peak areas
corresponding to the different crystal forms (see Figure 20). The higher temperature

endotherm corresponds to the fully extended molecule and the lower temperature

193

endotherm to the helical form. In solvent crystallization experiments, memory effects

were also observed. Systematic experiments are underway to study these behaviors.

The mechanism of the crystal formation from the melt can be explained as
follows. When the sample is melted, both kinds of segments start to adopt their most
stable conformation. Therefore, a helical PEO core and planar zigzag alkyl chains were
always obtained. Crystals with this combination of conformations are kinetically favored
since no reorganization is required. When these crystals are annealed at room
temperature or higher, they were converted to the thermodynamically more stable
conformations — the fully extended molecule with a planar zigzag conformation
throughout the whole chain. It is not hard to see that this conformation is more uniform
and has a higher degree of symmetry. The cross sections of the packed molecules are

smaller because of this uniformity.
Summary of crystalline forms of triblock CXEO-IC, oligomers

These triblock oligomers all crystallize in lamellar structures. The PEO core of
this series of oligomers can adopt either helical or planar zigzag conformations depending
on the crystallization conditions. When crystallized from polar solutions or isothermally
crystallized close to the melt-crystallization equilibrium temperature, the oligomers adopt
a fully extended structure with a trans zigzag conformation throughout the molecules.
When crystallized from non-polar solvents or from the melt with large supercooling, the
oligomers crystallize with the PEO core in the conformation of a 72 helix flanked by alkyl
groups in their usual planar zigzag conformation. The alkyl chains are tilted with respect

to the PEO helix axis. The tilt angle was 21° for crystal from hexane and 10° for crystals

194

formed by quenching from the melt. The fully extended crystal is the thermodynamically

stable crystal.
3. ABA oligomers CXEOny with y > 7

Seven ethylene oxide units are needed to make the perfect 72 helix for the PEO
core in the oligomers. Moreover, the geometry of the PEO structure also sets the two
planar zigzag alkyl chains parallel to each other. The oligomers can be crystallized in a
form that contains both helical and planar zigzag segments. When there are less than the
7 ethylene oxides needed to complete one 72 helix repeat unit, it is unfavorable for the
PEO core to adopt a helical form since the two alkyl chain can not align parallel to each
other. When the number of ethylene oxide units is > 7, it is easy to form the helical
conformation. Even for the oligomers with non-integer multiples of 7, the colinear
problem can be easily accommodated by small adjustments of each PEO segment.
Plotted in Figure 80 are the d-spacings for a series of C14EO,C14 oligomers measured by
powder XRD. Also plotted in the figure are the calculated molecular end to end distances
of the oligomers assuming either a helical or a planar zigzag conformation for the PEO
core. The alkyl chains are adjusted to be colinear with the PEO helix axis for calculation
of oligomers with helical PEO cores. From the figure, we can see that when y S 7, the d-
spacings fit the calculated values for fully extended molecules, while when y 2 7, the d-
spacings fit the calculated curve of molecules with helical PEO. The transformation can

be seen happening at 7 ethylene oxide units.

Raman spectroscopy also showed that all triblock oligomers with more than seven
ethylene oxide units have a helical PEO core. The spectrum of oligomer C14E014C14 is

shown in Figure 81. For comparison, spectra of stretched and unstretched PEO and

195

oligomer C14EO7C14 (planar zigzag conformation for PEO) are also shown in the figure.
Through this comparison, we can conclude that the PEO segments of C14E014C14 are in a
helical conformation. A helical PEO conformation for oligomers with more than seven
ethylene oxide units is stable. Unlike the oligomers with 7 ethylene oxide units, it does
not convert to a planar structure when annealed at room temperature. The Raman spectra

shown in Figure 40 clearly indicated that this is true.

Therefore, the triblock oligomers with y 2 7 adopt a structure with a 72 helical
PEO core flanked by planar zigzag alkyl chains. Because of the good matches of the
calculated end to end distances and the measured d—spacings, the alkyl chains have a very

small tilt angle relative to the PEO helix axis if at all.

196

 

 

 

 

 

 

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197

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4. Melting trends and odd-even effects in triblock oligomers

The melting points for the series of ABA triblock oligomers are plotted in Figure
82. For samples with more than one melting transitions, the highest melting transition
temperature was used since it corresponds to the thermodynamically more stable crystal.
For a given length of alkyl group, the melting points of a series of ABA amphiphiles
show a weak dependence on the length of the PEG segment when x 2 10. In contrast,
increasing the length of the alkyl chain by two carbon atoms shifts the melting points for
a series to higher temperatures due to the low PEO fraction in these oligomers. The trend
in melting points is similar to that of the n-alkanes. For example, the melting points of
CgEO-ng and C10E07C10 are 9 and 22 °C; the corresponding melting points for C16 and
C20 are 18 and 38 °C. When ethylene oxide fraction is higher (x S 8), it will play a more
important role in determining the oligomer’s melting point. As the ethylene oxide
segment becomes longer, the melting points of the oligomers with different alkyl chain
length get closer. It is believed that when the ethylene oxide segment is long enough, the
melting points will finally converge to a temperature that is very close to the melting

point of pure PEO.

Another feature of the melting point data is the oscillation of the melting points
within a series. ABA molecules with odd values of y have systematically higher melting
points than those where y is even when x S 12 or y S 6. Odd even effects are commonly
seen in the melting points of n-alkanes and molecules like liquid crystals, where
chromophores or mesogens are linked with short alkyl chains in a planar zigzag
conformation. In the ABA oligomers, the odd-even effect originates in the PEG segment,

where an odd number of EO units correspond to an even number of oxygen atoms and a

199

relatively high melting point. The odd-even effect can be understood by treating the
oxygen atoms in the chain as defects in a linear alkane caused by the difference in the C-
O-C bond angle relative to that of the C-C-C bond angle. Because the ABA chains adopt
a planar zigzag conformation when y S 7, successive oxygen atoms are anti to each other,
effectively canceling the distortions. Thus, ABA amphiphiles with odd values of y are
more linear and have higher melting points. When the alkyl chains are longer, the
bending of the molecule can be better accommodated with a series of small distortions
along the alkyl chain. The molecule looks more linear when the alkyl chains are longer.
A calculated result is shown in Figure 83: oligomer C3E04C3 bends 3° throughout the

molecule while oligomer C16E04C16 only bends 1°.

The odd-even effect can also be seen from trends in the heats of fusion for the
oligomers. Theoretical heat of fusion values were estimated by a linear combination of

PE and PEO’s heat of fusion based on their mole fractions. The heat of fusion for PE is

7.70 kJ/tnoil72 and the heat of fusion for PEO is 8.04 kJ/tnol.172 Since no heat of
fusion for planar zigzag PEO is available, we instead used the value for PEO. This may
cause some error in the estimation, but the trend for the series should hold. The
calculated and the measure heats of fusion are listed in Table 16. To better illustrate the
odd-even effect trend, the percentage difference in the calculated and experimental heats
of fusion values are plotted in Figure 84 versus number of ethylene oxide units for
oligomers CgEOng and C14EOyC14. The odd-even effect in oligomers with 8 carbon
alkyl chains is obvious. The experimental heats of fusion of oligomers with odd number
ethylene oxide are closer to the calculated value than those with even numbers. This

again can be explained by a planar zigzag PEO conformation in the oligomer. The

200

oligomers with odd number of ethylene oxide are more linear which enables them to pack
better in the crystal structure, thus higher heats of fusion. This trend is lost for oligomers
with longer alkyl chains because the long chains can achieve a linear structure through

small changes in the bond angles of the alkyl chains.

Table 16. Calculated and measured heats of fusion* for CxEOyCx oligomers.

 

 

 

 

 

 

 

 

 

 

 

 

 

(kJ/mol)

y 6 8 10 12 14 16

2 55/27 70/35 85/62 101/79 116/89 132/105
3 63/47 78/57 93/67 109/94 124/105 140/124
4 71/38 86/54 101/65 117/93 132/111 148/105
5 79/45 94/70 1 10/78 125/103 140/1 17 156/127
6 87/37 102/57 118/81 133/103 148/121 164/123
7 95/48 110/68 126/87 141/95 156/118 172/142
8 103/44 118/65 13491 149/107 164/117 180/88

10 119/86 134/80 150/100 165/106 181/128 196/107
14 151/102 166/98 182/118 197/120 213/132 228/145

 

 

 

 

 

 

 

 

* the value on top is calculated, while the bottom number is from DSC

measurements .

201

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202

 

 

 

Oligomer C3E04C3 bend about 3° throughout the chain

 

Oligomer C16E04C16 bend about 1° throughout the chain

Figure 83. Bending of the triblock oligomers caused by the angle difference
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203

percent deviation

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(bottom).

204

14

III. Structure and properties of (AB)n microblock copolymers
1. Melting point trend compare to the triblock oligomers

In Figure 85, the melting points of polymer (CmEOy)ll and its unsaturated analog
(CnrtCttEOy)n are plotted together with model compounds C6EOyC6 and CmEoycm.
The melting points of unsaturated polymers with short ethylene oxide segment show an
odd-even effect that tracks that of the model compounds, but deviate from the model
compounds when the ethylene oxide segment is longer. On the other hand, the melting
points of the saturated polymers deviate from the model compounds when y = 2 and 3,

but then follow closely the model compounds. A weak odd-even effect is seen to y = 8.

In the unsaturated polymers, the double bond is actually acting as a breaking point
for the polymer repeat units since the regular molecular conformation is disrupted at the
double bonds. The polymer can be thought of as a series of triblock oligomers with short
alkyl chains linked by the carbon carbon double bonds. Therefore, the repeat unit looks
more like CsEOst. This explains why the unsaturated polymers behave more like the
compounds C6EOyC6 rather than like CloEOyCm. By analogy, the unsaturated polymer
with y S 5 should have conformation with a planar zigzag conformation in all the atoms
but the double bond carbons. The odd-even effect originates from the trans PEO
conformation. When the PEO segment is longer, the polymer melting points deviate
from that of the model compounds, meaning that they may have different structures than

the model compounds.

205

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In the saturated polymers, the double bonds are removed, and there are no defects
in the molecules. The polymer chain can pack just like the model compounds. When the
PEO segments are very short, they played a small role in crystallization, and the
microblock copolymers behave more like a PE homOpolymer. Therefore, the melting
points of these polymers actually are more like those of long chain n-alkanes, which will
be higher than those of the model compounds. When the ethylene oxide segment is
longer, real diblock properties start to show. The polymers are more like a serial
connection of the corresponding model compounds. The melting point trend now follows

exactly that of the model compounds.

These resemblance of the polymers to model triblock oligomers validates our use
of these oligomers to study the polymer properties. The properties of these oligomers can
help explain the complicated properties of structurally similar crystalline (AB)n
microblock copolymers and provide molecular design rules for the preparation of

crystalline polymers with defined crystalline structures.
2. Polymer structure controls

Now that we know that the polymers resemble to a certain extent the triblock
oligomers, we would like to see if we could use the same method to manipulate the PEO

conformation in the polymers.

The unsaturated polymer (C9KC9EOy)n was crystallized from the melt, methanol
and hexane. The samples were studied with Fl" IR and XRD. The IR spectra shown in
Figure 47 for all samples are basically the same. The IR bands indicate that the PEO
segments in this polymer are in a helical conformation. The XRD results (Figure 58 and

59) show that they all have very similar d-spacings, 42.4 A, although the wide angle

207

XRD show some differences in details of the XRD pattern. It seems that the PEO
conformation manipulations that were used in the model system failed for this

unsaturated polymer.

The unsaturated polymer was then reduced to its saturated analog, (CmEO7).., and
was crystallized from methanol and hexane. For this sample, XRD shows no long d-
spacing feature. However, in IR spectra, we do observe distinct differences. As shown
in Figure 71, both spectra have bands at 718 cm", an indication of planar zigzag packing
for PB. The major differences are the bands between 1185 and 1085 cm". Samples
crystallized from hexane show two equal intensity bands at 1144 and 1115 cm", very
similar to the absorptions in the unsaturated polymer and model compounds with a
helical PEO conformation. Therefore, this sample should have helical PEO segments.
For the sample crystallized from methanol, the peak at this region is basically a singlet,

and the sample should have a planar zigzag PEO conformation.

To understand why the conformation control experiment could not get the desired
result for the unsaturated polymer, we have to study the detailed structure of the polymer.
Compared to the model compound, the major structural difference in this unsaturated
polymer is that there is a double bond in the middle of every alkyl segment. Since this
double bond can not have the same conformation as the rest of the alkyl chain, it acts as a
defect for the alkyl segment packing. As shown in Figure 86, double bonds lead to some
voids in the packing of the unsaturated polymer chains even if they are all in trans
configuration. The polymer still has about 15% of the double bonds with a cis geometry,
which can worsen the packing situation. Recall the mechanism for the crystallization of

model compound in polar solution, where the alkyl chains crystallize first and then

208

provides a template that essentially locks the PEO into the planar zigzag conformation. It
is impossible for that to happen in the unsaturated polymer with the poor packing caused
by double bond defects. With the void in the system, the alkyl chains can not pack
tightly and therefore when the PEO segments crystallize, there are enough spaces for
them to adopt their preferred helical conformation. Not surprisingly, when the double
bonds are removed, all the template effects work the same as in the model compounds
and PEO segments with different conformation were obtained. The deviation caused by
the unsaturation already showed in the comparison of their melting points with model
compounds. When the PEO segments are longer than 6 repeat units, instead of increasing
a little like in the model compounds, the melting points of the unsaturated polymers
jumped to a new level that is closer to those in the model compounds with longer alkyl

segments (Figure 85). It is believed that the PEO segments take charge of the crystal

melting point when y 2 6.

For all of the samples of (CnrchEOy).I crystallized with different methods, XRD
showed a long d-spacing of 42.4 A which indicated that there is some periodicity in this
range. Since we already know that the PEO segments are in a 72 helix, we estimate the
periodicity of the polymer chain given a helical PEO conformation. One of the obvious
repeating periods in this molecule is the repeating pattern of the segments between two
double bonds. The calculated distance from the first double bond carbon to the second
double bond carbon in the next repeat unit is longer than the 42.4 A d-spacing. We
estimated the packing by treating the unsaturated polymer the same way as in the model
compounds by tilting the alkyl chains with respect to the PEO helix axis. As shown in

Figure 87, by tilting the alkyl chains 23° relative to PEO helix axis, the d-spacing agrees

209

well with the repeating distance of the polymer between two double bonds. It is also
good to see that the tilt angle is very close to that in the model compound. The
hypothetical packing model of the unsaturated polymers is shown in Figure 88. When the
polymer is reduced, the periodicity of the double bonds is lost, and the d-spacing for the
polymer should correspond to the lamellar thickness of the polymer crystal which is in
the order of hundreds of angstroms. This distance is outside the range of the XRD
measurement we used. No distinct feature in our measuring range can be ascribed to the

long spacing.

210

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212

Figure 88. Packing model of unsaturated polymers (C91tC9EOy)n in crystalline state

3. Multiple thermal transitions of the polymers

Multiple transitions are seen for both saturated and unsaturated polymers,
especially when the PEO segments are short (see Figures 48-51 collectively). For
polymers, there are two possible explanations for this behavior—lamellae thickening and

thinning caused by chain folding, and polymorphism.

Since the multiplicity of the DSC endotherms disappeared when the ethylene
oxide segments become longer, it is likely that the multiple transitions are originated
from the PEO segments. In our low temperature XRD experiments (Figure 61 and 73),
we tried to observe changes for the polymers at different stages similar to the heating
process in DSC experiments. Peaks emerged as crystallization occurred during the
experiments. The peaks were similar in pattern to the PEO diffraction and the pattern
remained the same throughout the heating process before melting with very small shifts
in position. We think the crystal packing pattern is not changed significantly during the
transitions. This may let us infer that the transitions belong to lamellae thickening or
thinning since only they will substantially change the longer d-spacings without much
effect on the packing patterns. The process could also belong to the transformation of
non-integer folded to integer folded lamellae. One of the transformations in the
annealing of polymer (C10E06)n and (C10E07)n can probably be ascribed to this change.
For example, polymer (C10E07).. shows (in Figure 67) a melting transition that peaks at
15 °C after cooling at 10 °C/min. However, during the annealing at 0 °C, this peak

disappeared and was replaced by a transition at 9 °C. Annealing usually generates

crystals with better packing and higher melting transition. Cheng et al.117‘1229173

reported for a series of PEO samples, that mainly non-integer folded crystals were

213

generated during fast cooling or low temperature crystallization. These crystals can be
annealed to integer folded crystals during annealing process. The lamellar thickness can
either increase or decrease during this process. As the crystallization temperature
increased, the formation of the higher melting crystal with least folding increased.
However, at a certain crystallization temperature, formation of the high melting crystal
was depressed which is very similar to our polymer case. We think that these transitions
correspond to lamellar thinning or thickening. The crystal at 15 °C corresponds to a
folded crystal that converted to a thinner lamellar thickness crystal that melts at 9 °C. We
should be able to see the long d—spacing change during this process, however, the
thickness of the polymer lamellae is outside the range of our XRD, and we were not able

to see this shifting.

Polymorphism can not be excluded at this stage since in model compounds,
crystals were in fact obtained with different melting points that originated from different
conformations of the molecular structures. Giving the good resemblance of the melting
point trends of the polymers and model compounds, similar transformations may also
occur in the polymer. Further experiments are needed to fully clarify the nature of these

transitions.

IV. Comparison to other structurally similar (AB)n copolymers

The polymers prepared in this work are most closely related to the thioethylene-

segmented polymers (CXES,)n prepared by Mathias et al.144,145 which differ structurally
only in that oxygen has been replaced by sulfur. For these polymers, a single exothermic

transition was observed between two endothermic transitions, and polarized optical

214

microscopy indicated that at least some order was maintained up to the highest melting
transition. A series of model compounds (CloESyClo) were prepared and studied to
elucidate the structural transformations detected by DSC and microscopy. Vibrational
spectroscopy studies of the model compound with the shortest thioethylene segment,
CIOESIC 10. showed that it adopted a trans conformation for the thioethylene core, just as
we observed for the oxygenated analogs. However, the remaining compounds reveal
crucial differences between the oxyethylene and thioethylene systems. The x-ray
diffraction patterns of the CmESyCm series show no distinct low angle reflections that can
be attributed to a lamellar structure, and thus the details of the packing arrangement must
be different. In addition, two melting transitions are observed for the CmES3Cm and
CIOES4C10 model compounds. Based on solid state NMR experiments, planar structures
were assigned for these models in the temperature range between the two melting
transitions. At room temperature, (below the lowest melting transition), vibrational
spectroscopy and NMR data indicate that the thioethylene segments are increasingly
dominated by gauche conformations as the length of segments increase. Consistent with
that assignment is the absence of an odd-even effect for the melting points of the
polymers and model compounds, one of the signatures of the planar trans conformation
seen in the oxygenated compounds. The greater tendency to form helical conformations

in the thioethylene system has been ascribed to strong dipolar interactions between C-S-C

groups in adjacent chains. 147

In contrast, the fluorinated (AB)n polymers of Griffin et al.16()’161 exhibit

fundamentally different physical characteristics. Studies of the polymers and model

compounds160 show that the fluorocarbon segments are stiff due to the steric

215

stabilization of a helical structure for the (CF2)n segment. This rigidity leads to
mesophase formation that extends from the melting point of the alkyl segments to the
eventual melting (disordering) of the fluorocarbon segments. Thus, fluorinated (AB)n
microblock copolymers correspond to a combination of hard and soft blocks analogous to
thermoplastic polyurethanes, while the oxyethylene (AB)n system should be viewed as a
combination of flexible blocks. The conformational issues of the thioethylene and
oxyethylene (AB)n microblocks also are absent in the fluorinated systems; the methylenes
adopt a planar trans zig-zag conformation as expected and because of the homogeneous
character of the (C132)n segment, discussions about gauche conformations are replaced by

those of helix formation and periodicity.

216

EXPERIMENTAL

I. General Details

Unless otherwise specified, ACS reagent grade starting materials were used as
received from commercial suppliers. The reported melting points and boiling points are
uncorrected. Glassware used for the synthesis of Schrock’s molybdenum catalyst and
ADMET polymerizations were soaked in a potassium hydroxide/ethanol base bath

overnight, thoroughly rinsed with distilled water, and oven dried at 140 °C.

Proton and carbon nuclear magnetic resonance (1H and '3 C NMR) analyses were
carried out at room temperature in CDC13 on a Varian Gemini-300 spectrometer. The
chemical shifts were calibrated using residual CHC13 in the solvent and are reported
relative to tetramethylsilane. Infrared (IR) spectra for samples in solution were recorded
as CCl4 solutions under nitrogen at room temperature on a Nicolet IR/42 Fourier
Transform IR spectrometer. The spectrum of each pure compound was obtained by
subtracting the CC14 spectrum from that of the solution. Infrared spectra of solid samples
were measured on films prepared by evaporating a solution to dryness on a polished (19.4
mm diameter, 1.8 mm thick) silicon disk. The spectrum for each pure sample was

obtained by subtracting the silicon spectrum from that of the sample plus substrate.

Molecular weights of polymer samples were determined by gel permeation
chromatography (GPC) using a PLgel 20m Mixed A column at room temperature with

THF as eluting solvent at a flow rate of l mUmin. The concentration of the polymer

217

samples were 1 mg/mL. Detection was by a Waters R410 Differential Refractometer and

the results were calibrated with monodisperse polystyrene standards.
1. Thermal characterization of model compounds and polymers.

Therrnogravimetric analyses (TGA) of the polymers were obtained from a Perkin
Elmer TGA 7 instrument at a heating rate of 10 °C/min, usually in the temperature range
of 30 to 800 °C. DSC analyses of model compounds, monomers and polymers were
performed in aluminum pans under a helium atmosphere on a Perkin Elmer DSC 7
instrument, two-point calibrated with indium and hexyl bromide standards. The coolant
for the system was liquid nitrogen. Each sample was heated from room temperature to
100 °C at a rate of 10 °C/min, held at 100 °C for 5 minutes, quenched to -100 °C at a rate
of 200 °C/min, heated to 100 °C at a rate of 10 °C/min, cooled to -100 °C at a rate of 10

°C/min, and heated to 100 °C at a rate of 10 °C/min. The glass transition temperature, Tg,
was defined as midpoint temperature of the transition, and the melting point was taken as
the onset of the peak of the melting endotherm. Sample crystallinity and melting points
were studied by using a Nikon Optiphot2-POL polarizing optical microscope equipped
with a Mettler FP82-HT hot stage. The reported melting point range from microscopy
corresponds to the temperature where birefringence begins to be lost, and the temperature
where the sample becomes isotropic. The latter temperature correlates well with the
melting points determined by DSC. The heating rate used for melting point
determination was 10°C/min. Heats of fusion were calculated from the endothermic peak
using the accompanied functions of the DSC 7 software. Dynamic mechanical analyses
of polymer samples were performed on a Perkin Elmer DMA 7 instrument, calibrated

with an indium standard. DMA samples were held in a 8.5 mm diameter flat bottom

218

stainless steel cup and were probed with a 5 mm diameter flat top probe. DMA scans
were run under a helium flow. The coolant for the system was a mixture of liquid

nitrogen and dry ice.

XRD patterns were recorded on a Rigaku rotaflex 200B diffractometer equipped
with a rotating anode, Cu Kax-ray radiation (it = 1.541838 A) and a curved crystal
graphite monochromator. The x-ray instrument was operated at 45 kV and 100 mA.
Diffraction patterns were collected at 002° intervals between 1 and 15° values of 20 at a
scanning rate of 1° per minute and DS and SS slit widths of 1/6, and between 15 and 45°
values of 20 at DS and SS slit widths of 1/2. Powder samples were prepared by
spreading solid samples on the window of the glass sample holder with a spatula, or by
melting the sample directly on the window of the sample holder in an oven, and cooling
the holder to crystallize the sample as a film. XRD samples for low temperature
experiments were prepared by melting the polymer samples on the perforated copper
sample holder and flash-cooling to low temperature by immersion into liquid nitrogen.
The sample was installed while cold and the temperature was controlled at the desired

value and the XRD was recorded for each temperature.

2. Solvents

Reagent grade diethyl ether was distilled from sodium benzophenone ketyl under
nitrogen. Anhydrous dimethoxyethane (99.5%) was distilled from sodium benzophenone
ketyl under nitrogen. Reagent grade pentane (4 L) was vigorously stirred over
concentrated H2804 (300 mL), which was changed every 12 h until the acid remained
colorless. The pentane was then stirred over a 500 mL solution of KMnO4 (0.5 M) and

H2804 (3.0 M) for one day. After separation from the aqueous phase, the pentane was

219

washed with distilled water (4x500 mL), saturated aqueous NaHCO; (500 mL) and
distilled water (2x500 mL), and dried over anhydrous MgSO4. The pentane was filtered
and distilled from calcium hydride and then from sodium benzophenone ketyl under
nitrogen. THF was dried first by distilling from calcium hydride and then from sodium
benzophenone ketyl under nitrogen. Toluene was dried by distilling first from calcium

hydride and then from sodium benzophenone ketyl under nitrogen.
3. Argon

Argon used in air-sensitive reactions was deoxygenated by passing it through a 60
cm (8 cm in diameter) Mn0/Si02 column. The raw column filling material is Mn(NO3)2
blended with silica gel (60 - 200 mesh). The quartz column was wrapped with a heating
wire, filled with the raw filling material, and heated to at least 450 °C under a flow of
hydrogen gas. The color of the filling material turned from black to brown to green, and
moisture was evolved from the column. The generation process lasted about 10 h and
was followed by switching the H2 flow to argon for 2 h with continued heating. Traces of
H20 were removed by connecting the column to vacuum for 30 min. After it was used
for a period of time, the filling material in the column turned from green to brown, and

the column regeneration process was repeated.
4. Sodium mirrors

Sodium mirror coated Schlenk flasks were prepared by heating a piece of fresh
sodium metal (0.2 g) inside a clean flask with a hot plate under high vacuum until the

molten sodium vaporized and coated the walls of the flask.

220

5. Celite and Alumina packed funnel for monomer purification.

Celite® and Celite® acidic alumina mixtures (volume ratio 4/1) were dried in oven
at 140 °C overnight. A Schlenk-style fritted funnel was packed with successive layers of
Celite® (0.5 cm), Celite® and acidic alumina mixture (3 cm), Celite® (0.5 cm). The

packed funnel was placed under vacuum until used.

11. Synthesis of chemicals in this project
1. Synthesis of ethylene glycol oligomer ditosylates

Diethylene glycol ditosylate [Ts(OCH2CH2)2OTs, 2(2)]. A solution of
diethylene glycol (130 g, 1.22 mol) and p-toluenesylfonyl chloride (701 g, 3.66 mol) in
THF (1.5 L) was placed in a 3 L three necked round bottom flask and stirred
magnetically. The flask was cooled with an ice/water bath, and a solution of KOH (450
g, 8.00 mol) in water (500 mL) was added slowly over a period of 1h. The ice-water bath
was removed and the system was stirred for additional 7h. The resulting suspension was
poured into a mixture of 1 L CH2C12 and 500 mL ice water and the aqueous layer was
extracted with 2 250 mL portions of CHzClz. The combined organic solutions were
washed three times with distilled water, and dried over MgSO4 overnight. After removal
of MgSO4 and solvent, the solid was recrystallized twice from methanol to give 89%

yield of 2(3) as a white crystalline product. 1H NMR (300 MHz, CDCl3) 5 7.76 (d, 4H),
7.33 (d, 4H), 4.07 (t, 4H), 3.59 (t, 4H), 2.43 (s, 6H). mp 87.5-88.5 °C. (lit.174 87-87.5

°C).

221

Triethylene glycol ditosylate [Ts(OCH2CHz)3OTs, 2(3)]. 2(3) was prepared
similarly to give 87% yield of a white crystalline solid. lH NMR (300 MHz, CDC13) 8
7.77 (d, 4H), 7.32 (d, 4H), 4.12 (t, 4H), 3.63 (t, 4H), 3.51 (s, 4H), 2.43 (s, 6H). mp 80-81
°C. (lit.174 80-81 °C).

Ditosylates for y = 4 - 10 [Ts(OCH2CH2)yOTs, 2(y)]. Ditosylates 2(y) for y = 4
— 10 was prepared the same way as diethylene glycol ditosylate. After the reaction was
finished, 200 mL ice water was added, the solution was separated and the aqueous layer
was extracted with diethyl ether (3 x 100 mL). The combined organic solutions were
washed with saturated aqueous NaCl solution (3 X 200 mL) and dried over MgSO4

overnight. After removal of MgSO4 and solvent, a clear colorless to light yellow viscous

liquid was obtained. The product is pure enough for further use.

Tetraethylene glycol ditosylate [Ts(OCH2CH2)4OTs, 2(4)]. Yield 99%. Clear
colorless oll.175 1H NMR (300 MHz, CDC13) 5 7.78 (d, 4H), 7.32 (d, 4H), 4.12 (t, 4H),
3.65 (t, 4H), 3.57 (s, 4H), 3.54 (s, 4H), 2.43 (s, 6H).

Pentaethylene glycol ditosylate [Ts(OCH2CH2)50Ts, 2(5)]. Yield 99%. Clear
colorless oil. 176 ‘H NMR (300 MHz, CDCl3) 5 7.78 (d, 4H), 7.32 (d, 4H), 4.12 (t, 4H),
3.65 (t, 4H), 3.57 (s, 4H), 3.55 (s, 8H), 2.43 (s, 6H).

Hexaethylene glycol ditosylate [Ts(OCH2CH2)6OTs, 2(6)]. Yield 99%. Clear

colorless oil.177 'H NMR (300 MHz, CDC13) 6 7.78 (d, 4H), 7.32 (d, 4H), 4.12 (t, 4H),

3.65 (t, 4H), 3.58 (s, 4H), 3.55 (s, 12H), 2.43 (s, 6H).

222

Heptaethylene glycol ditosylate [Ts(OCH2CH2)7OTs, 2(7)]. Yield 99%. Clear

colorless oil.178 ‘H NMR (300 MHz, CDCl3) 8 7.78 (d, 4H), 7.32 (d, 4H), 4.12 (t, 4H),

3.65 (t, 4H), 3.56 (m, 20H) 2.43 (s, 6H).

Octaethylene glycol ditosylate [Ts(OCH2CH2)3OTs, 2(8)]. Yield 99%. Clear

colorless oll.165 'H NMR (300 MHz, CDC13) 5 7.78 (d, 4H), 7.32 (d, 4H), 4.12 (t, 4H),

3.65 (t, 4H), 3.56 (m, 24H) 2.43 (s, 6H).

Decaethylene glycol ditosylate [Ts(OCH2CH2)mOTs, 2(10)]. Yield 98%. Clear
colorless oil. ‘H NMR (300 MHz, CDC13) 5 7.78 (d, 4H), 7.32 (d, 4H), 4.12 (t, 4H), 3.65

(t, 4H), 3.56 (m, 32H), 2.43 (s, 6H).

Tetradecaethylene glycol ditosylate [Ts(OCH2CH2)14OTs,]. Ditosylate 2(14)
was prepared as described for tetraethylene glycol ditosylate except the reaction time was
extended to 16 hours. After the reaction was finished, a mixture of 10/1 CHzClz and ice
water was added to the reaction mixture until the solids dissolved. The organic layer was
separated, and the aqueous layer was extracted with CHzClz (3 x 100 mL). The
combined organic solutions were washed with saturated NaCl solutions (3 x 200 mL) and
dried over NazSO4 overnight. Removal of NaSO4 and solvent gave a clear, colorless,
viscous liquid product in 97% yield. 1H NMR (300 MHz, CDC13) 8 7.78 (d, 4H), 7.32 (d,

4H), 4.12 (t, 4H), 3.65 (t, 4H), 3.56 (m, 48H), 2.43 (s, 6H).

2. Ethylene glycol oligomer monotritylates and ditritylates.

Diethylene glycol monotritylate [Tr(OCH2CH2)2OH, 3(2)]. A 500 mL three

neck round bottom flask equipped with a mechanical stirrer, thermometer, and nitrogen

223

inlet was charged with di(ethylene glycol) (106 g, 1.00 mol) and pyridine (11.9 g, 0.150
mol). With the mixture heated and maintained at 45°C, powdered trityl chloride (27.9 g,
0.100 mol) was added to the reaction mixture under vigorous stirring. After stirring at 45
°C for 16 h, the suspension was filtered and the white solid was washed with distilled
water (5 x 50 mL). The crude product was recrystallized from isopropanol and twice
from 2/1 EtOAc/hexanes to give a white crystalline solid. Yield 71%. 1H NMR (300

MHz, CDCI3) 5 7.46 (d, 6H), 7.25 (m, 9H), 3.58-3.77 (m, 6H), 3.24 (t, 2H), 2.06 (t, 1H).

mp 1130-1145 °C (lit.165 112.7-114.5°C).

Triethylene glycol monotritylate [Tr(OCHzCH2)3OH,]. 3(3) was prepared as
describe for diethylene glycol monotritylate. After the reaction was finished, the reaction
mixture was poured into a separatory funnel and an equal volume of distilled water was
added. The mixture was shaken vigorously, and allowed to settle for 2 hours. The
bottom layer was separated from the aqueous solution, and the aqueous solution was
extracted with toluene (3 x 50 mL). The product was dissolved in toluene and combined
with the toluene extract. The toluene solution was washed with distilled and dried over
MgSO4 overnight. Removal of the solid and solvent gave a yellow viscous gel-like
liquid179 in 99% yield. The product was used for next reaction without further
purification. 1H NMR (300 MHz, CDC13) 5 7.46 (d, 6H), 7.25 (m, 9H), 3.59-3.75 (m,

10H), 3.22 (t, 2H), 1.70 (s, 1H).

Tetraethylene glycol monotritylate [Tr(OCH2CH2)4OH,]. 3(4) was prepared

and purified as describe for 3(4) to give a yellow viscous gel-like liquid180 in 99% yield.

224

1H NMR (300 MHz, CDC13) 5 7.46 (d, 6H), 7.20-7.45 (m, 9H), 3.25-3.15 (m, 12H), 3.12-

3.08 (t, 2H), 3.26 (t, 2H), 2.35 (s, 1H).

General procedure for the preparation of ditritylates. Heptaethylene glycol
ditritylate [Tr(OCH2CH2)7OTr, 4(7)]. A 500 ml. Schlenk flask with an argon inlet was
charged with NaH (3.00 g, 0.125 mol). A solution of diethylene glycol monotritylate
(34.8 g, 0.100 mol) in 200 mL THF was added dropwise and the mixture was stirred for
24 h. Ts(OCH2CH2)3OTs (23.0 g, 0.050 mol) in 150 mL THF was added dropwise, and
the mixture was stirred for 96 h at room temperature. The solid was removed by
filtration, and the organic filtrate was washed with saturated aqueous NaCl (3 x 150 mL),

dried over MgSO4, and concentrated to give a quantitative yield of 4(7) as a yellow gel-
like liquid.165 ‘H NMR (300 MHz, CDC13) 5 7.45 (d, 12H), 7.18-7.30 (m, 18H), 3.59-
3.69 (m, 24H), 3.19-3.25 (t, 4H).

Hexaethylene glycol ditritylate [Tr(OCH2CH2)6OT r, 4(6)]. A yellow gel-like
liquid,165 prepared by reacting Tr(OCH2CH2)20H with Ts(OCH2CH2)20Ts in 100%
yield. lH NMR (300 MHz, CDC13) 5 7.45 (d, 12H), 7.18-7.28 (m, 18H), 3.62 (m, 20H),
3.20 (t, 4H).

Octaethylene glycol ditritylate [Tr(OCHzCH2)sOTr, 4(8)]. A yellow gel-like

liquid,165 prepared by reacting Tr(OCH2CH2)20H with Ts(OCH2CH2)4OTs in 99%
yield. ‘H NMR (300 MHz, CDC13) 5 7.48 (d, 12H), 7.18-7.23 (m, 18H), 3.60-3.78 (m,

28H), 3.20-3.30 (t, 4H).

Nonaethylene glycol ditritylate [Tr(OCH2CH2)oOTr, 4(9)]. A yellow gel-like

liquid, prepared by reacting Tr(OCH2CH2)3OH with Ts(OCH2CH2)3OTs. Yield 98%. IH

225

NMR (300 MHz, CDC13) 5 7.45 (d, 12H), 7.18-7.30 (m, 18H), 3.58-3.69 (m, 32H), 3.19-

3.25 (t, 4H).

Decaethylene glycol ditritylate [Tr(OCH2CH2)loOTr, 4(10)]. A yellow gel-like
liquid, prepared by reacting Tr(OCH2CH2)4OH with Ts(OCH2CH2)2OTs. Yield 99%. 1H
NMR (300 MHz, CDCI3) 8 7.44 (d, 12H), 7.17-7.30 (m, 18H), 3.57-3.68 (m, 36H), 3.20

(t, 4H).

Tetradecaethylene glycol ditritylate [Tr(OCH2CH2)140Tr, 4(14)] was
prepared by reacting Tr(OCH2CH2)4OH with Ts(OCH2CH2)6OTs. Removal of the
MgSO4 and concentration of the solvent gave a brownish-yellow solution. The solution
was refluxed with charcoal overnight and filtered to give a colorless to light yellow
solution. Removal of the solvent gave a light yellow viscous gel-like liquid in 97% yield.
1H NMR (300 MHz, CDC13) 5 7.44 (d, 12H), 7.17-7.30 (m, 18H), 3.57-3.68 (m, 52H),

3.20 (t, 4H).

3. Exact length ethylene glycol oligomers:

General procedure for the synthesis of exact length ethylene glycol oligomers.
Heptaethylene glycol [H(OCH2CH2)7OH, 1(7)]. A high pressure Monel bomb with a
glass insert was charged with 36.6 g (45.0 mmol) heptaethyelene glycol ditritylate, 150
mL CHzClz, and 0.677g of 10% palladium on carbon. Hydrogenolysis was carried out at
room temperature under 50 atm Hz for 48 hours. Upon completion of the reaction, the
catalyst (which can be reused) was filtered and washed with CHzClz. The filtrate was

concentrated to give a mixture of a white solid (triphenylmethane) and an oil. The

226

mixture was dissolved in boiling methanol and the majority of the triphenylmethane
crystallized when the solution was cooled to 0 °C. The mixture was filtered and the
filtrate was washed with hexanes (6 x 100 mL) to remove trace amounts of

triphenylmethane. The solvent was removed to give a clear colorless oil. Yield 97%. bp

180-195 °C/50 mtorr. (lit.181 200-208 °C/3OO mtorr.) 1H NMR (300 MHz, CDC13) 5

372-367 (t, 4H), 3.66-3.61 (m, 20H), 3.60-3.55 (t, 4H), 2.9 (s, 2H).

Hexaethylene glycol [H(OCH2CH2)6OH, 1(6)]. A clear colorless oil. Yield
99%. 'H NMR (300 MHz, CDC13) 5 3.72-3.67 (t, 4H), 3.66-3.61 (m, 16H), 3.60-3.55 (t,
4H), 2.9 (s, 2H). bp 197-205 °C/100 mtorr (1it.182 201-205 0(:/700 mtorr).

Octaethylene glycol [H(OCH2CH2)30H, 1(8)]. A clear colorless oil. Yield

97%. 'H NMR (300 MHz, CD03) 5 3.72355 (m, 32H), 2.7 (s, 2H).

Nonaethylene glycol [H(OCH2CH2)90H, 1(9)]. A clear colorless oil. Yield

92%. 1H NMR (300 MHZ, CDC13) 5 3.72-3.55 (m, 36H), 2.7 (s, 2H).

Decaethylene glycol [H(OCH2CH2)100H, 1(10)]. A clear light yellow oil.

Yield 96%. 1H NMR (300 MHz, CDC13) 5 3.72-3.56 (m, 40H), 2.58 (s, 2H).

Tetradecaethylene glycol [H(OCH2CH2)14OH, 1(14)]. A white waxy solid.

Yield 96%. 1H NMR (300 MHz, CDC13) 5 3.72-3.56 (m, 56H), 2.58 (s, 2H). mp 37-39

°C.

227

4. Model compound syntheses:

Preparation of model compounds [CH3(CH2)X.1(OCHzCH2)yO(CH2),.1CH3,
CxEony]. Under Ar, the appropriate ethylene glycol oligomer (5.00 mmol) in 20 mL of
dry THF was added dropwise to a 100 mL Schlenk flask charged with NaH (12.5 mmol).
The reaction mixture was stirred for 24 h, and then the appropriate alkyl bromide (10.2
mmol) in 15 mL THF was added and stirred for 72 h at room temperature, or at reflux (y
= 2,3). Upon completion of the reaction, 5 mL of water were added slowly and the
solution was stirred for 10 min. The layers were separated and the water layer was
extracted with ether (3x20 mL). The combined organic solutions were washed with
saturated NaCl solution (2x80 mL), dried over MgSO4, and concentrated. Hexyl and
octyl derivatives (y = 2, 3, 4, 5,) were distilled under vacuum to give clear colorless oils.
All other compounds were recrystallized from acetone (y = 2, 3), or methanol (y = 4, 5, 6,
7, 8, 10, 14) at low temperature. Liquid products are clear colorless and solid products

are white and crystalline. The melting points of all model compounds were determined

by DSC.

CoEOng. A clear colorless liquid. Yield 53%. 1H NMR (300 MHz, CDC13) 5
3.62 (m, 4H), 3.57 (m, 4H), 3.42 (t, 4H), 1.49-1.59 (quintuplet, 4H), 1.20-1.34 (m, 12H),

0.86 (t, 6H). mp —25.9 °C.

C3E02C3.. Yield 52%. 1H NMR (300 MHz, CDC13) 5 3.62 (m, 4H), 3.57 (m, 4H),

3.42 (t, 4H), 1.50-1.60 (quintuplet, 4H), 1.20—1.32 (m, 20H), 0.86 (t, 6H). mp —1.9 °C.

CroEosz. A clear colorless liquid. Yield 77%. 1H NMR (300 MHz, CDC13) 5

3.62 (m, 4H), 3.57 (m, 4H), 3.41 (t, 4H), 1.20-1.60 (m, 32H), 0.86 (t, 6H). mp 19.5 °C.

228

 

C12E02C12. A white crystalline solid. Yield 79%. lH NMR (300 MHz, CDC13) 5

3.62 (m, 4H), 3.57 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 40H), 0.86 (t, 6H). mp 31.6 °C.

C14E02C14. Yield 82%. lH NMR (300 MHz, CDC13) 5 3.63 (m, 4H), 3.57 (m,

4H), 3.42 (t, 4H), 1.20-1.60 (m, 48H), 0.86 (t, 6H). mp 41.5 °C.

CmEOsz. A white crystalline solid. Yield 85%. lH NMR (300 MHz, CDCl3) 5

3.62 (m, 4H), 3.57 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 56H), 0.86 (t, 6H). mp 50.1 °C.

C6EO3C6. A clear colorless liquid. Yield 55%. lH NMR (300 MHz, CDC13) 5
3.60-3.65 (m, 8H), 3.57 (m, 4H), 3.42 (t, 4H), 1.49-1.59 (quintuplet, 4H), 1.20-1.34 (m,

12H), 0.86 (t, 6H). mp —16.1 °C.

C3E03Cg. A clear colorless liquid. Yield 53%. 1H NMR (300 MHz, CDC13) 5
3.60-3.65 (m, 8H), 3.57 (m, 4H), 3.42 (t, 4H), 1.49-1.60 (quintuplet, 4H), 1.20-1.32 (m,

20H), 0.86 (t, 6H). mp 5.0 °C.

C10E03C10. A white crystalline solid. Yield 59%. 1H NMR (300 MHz, CDC13) 5
3.60-3.65 (m, 8H), 3.57 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 32H), 0.86 (t, 6H). mp 22.0
°C.

C12E03C12. A white crystalline solid. Yield 72%. 1H NMR (300 MHz, CDC13) 5
3.60-3.65 (m, 8H), 3.57 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 40H), 0.86 (t, 6H). mp 33.6
°C. (lit.183 35.7-36.2 °C)

C14EO3C14. A white crystalline solid. Yield 85%. 'H NMR (300 MHz, CDC13) 5
3.60—3.65 (m, 8H), 3.57 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 48H), 0.86 (t, 6H). mp 42.7

°C.

229

C16E03C16. A white crystalline solid. Yield 82%. 1H NMR (300 MHz, CDC13) 5
3.60-3.65 (m, 8H), 3.57 (m, 4H), 3.42 (t, 4H), 1.19-1.60 (m, 56H), 0.86 (t, 6H). mp 50.9

°C.

CnEOan. A clear colorless liquid. Yield 50%. 1H NMR (300 MHz, CDC13) 5
3.59-3.66 (m, 12H), 3.57 (m, 4H), 3.42 (t, 4H), l.49-1.59 (quintuplet, 4H), 1.20-1.34 (m,

12H), 0.86 (t, 6H). mp -21.9 °C.

C8E04C3. A clear colorless liquid. Yield 52%. 1H NMR (300 MHz, CDCl3) 5
3.59-3.66 (m, 12H), 3.57 (m, 4H), 3.42 (t, 4H), 1.50-1.60 (quintuplet, 4H), 1.20-1.32 (m,

20H), 0.86 (t, 6H). mp 3.6 °C.

CroanCm. A clear colorless liquid. Yield 71%. ‘H NMR (300 MHz, CDCl;) 5

3.62 (m, 12H), 3.57 (m, 4H), 3.41 (t, 4H), 1.20-1.60 (m, 32H), 0.86 (t, 6H). mp 19.4 °C.
C12E04C12. A white crystalline solid. Yield 84%. 'H NMR (300 MHz, CDCl3) 5
3.62 (m, 12H), 3.57 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 40H), 0.86 (t, 6H). mp 33.4 °C.
(lit. 184 33-34 °C)
C14E04C14. A white crystalline solid. Yield 85%. 1H NMR (300 MHz, CDCI3) 5

3.60-3.65 (m, 12H), 3.57 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 48H), 0.86 (t, 6H). mp

42.0 °C.

C15E04C16. A white crystalline solid. Yield 82%. 1H NMR (300 MHz, CDCl3) 5
3.60-3.65 (m, 12H), 3.57 (m, 4H), 3.42 (t, 4H), 1.18-1.60 (m, 56H), 0.86 (t, 6H). mp

48.6 °C.

230

 

CsEOSCs. A clear colorless liquid. Yield 46%. ‘H NMR (300 MHz, CDCl3) 5
3.59-3.67 (m, 16H), 3.56 (m, 4H), 3.42 (t, 4H), 149—1.59 (quintuplet, 4H), 1.20-1.34 (m,

12H), 0.86 (t, 6H). mp —l4.7 °C.

CgEOng. A clear colorless liquid. Yield 52%. 1H NMR (300 MHz, CDC13) 5
3.59-3.67 (m, 16H), 3.56 (m, 4H), 3.42 (t, 4H), 1.49-1.60 (quintuplet, 4H), 1.20-1.32 (m,

20H), 0.86 (t, 6H). mp 9.3 °C.

cmEoscm. A white crystalline solid. Yield 79%. 1H NMR (300 MHz, CDCl3) 5
3.59-3.67 (m, 16H), 3.56 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 32H), 0.86 (t, 6H). mp

21.4 °C.

CrzEOsCrz. A white crystalline solid. Yield 81%. 1H NMR (300 MHz, CDC13) 5

3.59-3.67 (m, 16H), 3.56 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 40H), 0.86 (t, 6H). mp

32.8 °C. (lit.184 33-34 °C)

CrrEoscr... A white crystalline solid. Yield 91%. 1H NMR (300 MHz, CDC13) 5
3.59-3.67 (m, 16H), 3.56 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 48H), 0.86 (t, 6H). mp

41.1°C.

CmEOsCm. A white crystalline solid. Yield 94%. 1H NMR (300 MHz, CDC13) 5
3.59-3.67 (m, 16H), 3.56 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 56H), 0.86 (t, 6H). mp

46.9 °C.

C6E06C6. A clear colorless liquid. Yield 39%. lH NMR (300 MHz, CDC13) 5
3.59-3.66 (m, 20H), 3.57 (m, 4H), 3.42 (t, 4H), 1.49-1.59 (quintuplet, 4H), 1.20-1.34 (m,

12H), 0.86 (t, 6H). mp —11.5 °C.

231

CgEOng. A clear colorless liquid. Yield 41%. 1H NMR (300 MHz, CDC];;) 5
3.59-3.66 (m, 20H), 3.57 (m, 4H), 3.42 (t, 4H), 1.49-1.60 (quintuplet, 4H), 1.20-1.32 (m,

20H), 0.86 (t, 6H). mp 6.4 °C.

CroEOng. A white crystalline solid. Yield 78%. 1H NMR (300 MHz, CDCl3) 5
3.62 (m, 20H), 3.57 (m, 4H), 3.41 (t, 4H), 1.20-1.60 (m, 32H), 0.86 (t, 6H). mp 21.8 °C.
(1it.185 30 °C)

C12E06C12. A white crystalline solid. Yield 90%. 1H NMR (300 MHz, CDC13) 5
3.62 (m, 20H), 3.57 (m, 4H), 3.41 (t, 4H), 1.20-1.60 (m, 40H), 0.86 (t, 6H). mp 31.2 °C.
(lit.185 33.5 °C)

C14E06C14. A white crystalline solid. Yield 90%. lH NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 20H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 48H), 0.86 (t, 6H). mp
40.2 °C. (1it.185 43 °C)

CmEOrCm. A white crystalline solid. Yield 92%. 1H NMR (300 MHz, CDC13) 5
3.58-3.65 (m, 20H), 3.55 (m, 4H), 3.41 (t, 4H), 1.54 (quintuplet, 4H), 1.18-1.32 (m,
52H), 0.85 (t, 6H). mp 46.4 °C. (lit. 18643 °C)

C6E07C6. A clear colorless liquid. Yield 60%. ‘H NMR (300 MHz, CDC13) 5

3.59-3.65 (m, 24H), 3.55 (m, 4H), 3.42 (t, 4H), 1.49-1.59 (quintuplet, 4H), 1.20-1.34 (m,

12H), 0.86 (t, 611). mp -2.6 °C.

C3EO7C3. A clear colorless liquid. Yield 64%. lH NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 24H), 3.55 (m, 4H), 3.42 (t, 4H), 1.49-1.60 (quintuplet, 4H), 1.20-1.32 (m,

20H), 0.86 (t, 6H). mp 9.4 °C.

232

 

CloEO7Cm. A white crystalline solid. Yield 80%. 1H NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 24H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 32H), 0.86 (t, 6H). mp

22.0 °C.

CrzEO-rClz. A white crystalline solid. Yield 88%. lH NMR (300 MHz, CDCl3) 5

3.59-3.65 (m, 24H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 40H), 0.86 (t, 6H). mp

32.3 °C. (lit.l87 32.5 °C)

C14E07C14. A white crystalline solid. Yield 88%. 1H NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 24H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 48H), 0.86 (t, 6H). mp

41.3 °C.

C16E07C16. A white crystalline solid. Yield 91%. 1H NMR (300 MHz, CDC13) 5
3.60-3.65 (m, 24H), 3.55 (m, 4H), 3.41 (t, 4H), 1.54 (m, 4H), 1.18-1.32 (m, 52H), 0.85 (t,

6H). mp 44.8 °C.

C6E03C6. A clear colorless liquid. Yield 62%. lH NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 28H), 3.55 (m, 4H), 3.42 (t, 4H), l.49-1.59 (quintuplet, 4H), 1.20-1.34 (m,

12H), 0.86 (t, 6H). mp 2.2 °C.

C3E03Cs. A clear colorless liquid. Yield 62%. 1H NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 28H), 3.55 (m, 4H), 3.42 (t, 4H), l.49-1.60 (quintuplet, 4H), 1.20-1.32 (m,

20H), 0.86 (t, 6H). mp 13.6 °C.

CroEOng. A white crystalline solid. Yield 81%. 1H NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 28H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 32H), 0.86 (t, 6H). mp

23.7 °C.

233

C12E03C12. A white crystalline solid. Yield 87%. lH NMR (300 MHz, CDCl3) 5
3.59-3.65 (m, 28H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 40H), 0.86 (t, 6H). mp

30.9 °C. (Lit.183 33.8-34.3 °C)

C14E03C14. A white crystalline solid. Yield 91%. 1H NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 28H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 48H), 0.86 (t, 6H). mp

38.8 °C.

CrsEOsCrs. A white crystalline solid. Yield 89%. 'H NMR (300 MHz, CDCl3) 5
3.60-3.65 (m, 28H), 3.55 (m, 4H), 3.41 (t, 4H), 1.54 (m, 4H), 1.18-1.32 (m, 52H), 0.85 (t,

6H). mp 40.4 °C.

canmca A clear colorless liquid. Yield 70%. 'H NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 36H), 3.55 (m, 4H), 3.42 (t, 4H), 1.49-1.59 (quintuplet, 4H), 1.20-1.34 (m,

12H), 0.86 (t, 6H). mp 15.7 °C.

CgEOng. A white crystalline solid. Yield 69%. 'H NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 36H), 3.55 (m, 4H), 3.42 (t, 4H), 1.49-1.60 (quintuplet, 4H), 1.20-1.32 (m,

20H), 0.86 (t, 6H). mp 21.1 °C.

CmEOroCm. A white crystalline solid. Yield 78%. 1H NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 36H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 32H), 0.86 (t, 6H). mp

26.7 °C.

CnEOmCrz. A white crystalline solid. Yield 83%. lH NMR (300 MHz, CDC13) 5
3.59-3.65 (m, 36H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 40H), 0.86 (t, 6H). mp

35.0 °C. (Lit.183 36.5-37 °C)

234

Crammer... A white crystalline solid. Yield 85%. 1H NMR (300 MHz, CDCl3) 5
3.59-3.65 (m, 36H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 48H), 0.86 (t, 6H). mp

40.5 °C.

C16E010C16. A white crystalline solid. Yield 87%. 1H NMR (300 MHz, CDC13) 5
3.60—3.65 (m, 36H), 3.55 (m, 4H), 3.41 (t, 4H), 1.54 (m, 4H), 1.18-1.32 (m, 52H), 0.85 (t,

6H). mp 43.6 °C.

C6E014C6. A white waxy solid. Yield 73%. 1H NMR (300 MHz, CDC13) 5 3.59-
3.65 (m, 52H), 3.55 (m, 4H), 3.42 (t, 4H), l.49-1.59 (quintuplet, 4H), 1.20-1.34 (m,

12H), 0.86 (t, 6H). mp 26.5 °C.

C3E014C3. A white waxy solid. Yield 74%. 1H NMR (300 MHz, CDC13) 5 3.59-
3.65 (m, 52H), 3.55 (m, 4H), 3.42 (t, 4H), 1.49-1.60 (quintuplet, 4H), 1.20-1 32 (m,

20H), 0.86 (t, 6H). mp 26.0 °C.

C10E014C10.A white crystalline solid. Yield 80%. 'H NMR (300 MHz, coch) 5
3.59-3.65 (m, 52H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 32H), 0.86 (t, 6H). mp

35.5 °C.

C12E014C12. A white crystalline solid. Yield 84%. 1H NMR (300 MHz, CDCl3) 5
3.59-3.65 (m, 52H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 40H), 0.86 (t, 6H). mp

38.5 °C.

C14E014C14. A white crystalline solid. Yield 84%. 1H NMR (300 MHz, CDCl3) 5
3.59-3.65 (m, 52H), 3.55 (m, 4H), 3.42 (t, 4H), 1.20-1.60 (m, 48H), 0.86 (t, 6H). mp

43.5 °C.

235

C16E014C16. A white crystalline solid. Yield 86%. .H NMR (300 MHz, CDC13) 5
3.60-3.65 (m, 52H), 3.55 (m, 4H), 3.41 (t, 4H), 1.54 (m, 4H), 1.18-1.32 (m, 52H), 0.85 (t,

6H). mp 47.5 °C.

5. General procedure for monomer syntheses and purification.

Hexaethylene glycol 0t,(l)-dibutenyl ether [rtConngn]. A 2 L round bottom
flask equipped with an addition funnel with a N2 inlet and outlet was charged with 95%
NaH (6.19 g, 0.250 mol) in dry THF (200 mL). To the stirred slurry, a solution of 3-
buten-l-ol (14.4 g, 0.200 mol) in 200 mL THF was added dropwise and stirred for 24 h,
Hexaethylene glycol onto-ditosylate (58.0 g, 0.0980 mol) in 1 L THF was added. The
addition funnel was replaced with a cold water condenser with an AI inlet and outlet and
the reaction mixture was refluxed for 5 days. The product was filtered and the clear
brown solution was washed with saturated aqueous NaCl (4 X 150 mL) and dried over
Mg804 overnight. Filtration and removal of the solvent gave a yellow oil which was
further purified by column chromatography (75/25 EtOAc/hexanes). The resulting
yellow oil product was dissolved in hexanes and stirred over a freshly made sodium
mirror under Ar overnight. The mixture was filtered under Ar through a funnel packed
with Celite and alumina. The process was repeated (2 to 3 times) until the filtrate was
colorless. The solvent was removed from the filtrate in vacuo to give a 34% yield (13.0
g) of a clear colorless liquid. The purified monomer was stored in dry box under helium

until used. 1H NMR (300 MHz, CDC13) 5 5.88-5.70 (m, 2H), 5.10-4.98 (m, 4H), 3.65-

3.60 (m, 20H), 3.59-3.52 (m, 4H), 3.52-3.47 (t, 4H), 2.37-2.27 (m, 4H). mp -10.1 °C.

236

All the other monomers were prepared in the same way. Since the monomers
derived from tetradecaethylene glycol series are not soluble in hexanes, dry toluene was

used in the sodium mirror process for this series.

nC3E05C31t. Isolated by column chromatography (silica gel, ethyl acetate) as a
clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid. Yield
24.2g (59%). 1H NMR (300 MHz, CDC13) 5 5.86-5.70 (m, 2H), 5.04-4.90 (m, 4H), 3.65-
3.59 (m, 20H), 3.58-3.53 (m, 4H), 3.47-3.41 (t, 4H), 2.13-2.03 (m, 4H), 1.71-1.60 (m,

4H). mp -139 °C.

nC4E06C41t. Isolated by column chromatography (silica gel, EtOAc : hexanes = 3
: l) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 23.0 g (53%). 1H NMR (300 MHz, CDC13) 5 5.86-5.71 (m, 2H), 5.02-4.89 (m,
4H), 3.65-3.59 (m, 20H), 3.57-3.53 (m, 4H), 3.46-3.40 (t, 4H), 2.09-2.00 (m, 4H), 1.63-

1.52 (m, 4H), 1.47-1.35 (m, 4H). mp —11.5 °C.

ltCsEosCsn. Isolated by column chromatography (silica gel, EtOAc : hexanes = 1
: 1) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 30.9 g (57%). 1H NMR (300 MHz, CDC];,) 5 5.86-5.71 (m, 2H), 5.01-4.87 (m,
4H), 3.65-3.59 (m, 20H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), 1.40-1.20 (m, 20H). mp 3.6 °C.

nCoEOrsCon. Isolated by column chromatography (silica gel, EtOAc : hexanes = 1
: l) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.

Yield 23.8 g (41%). 1H NMR (300 MHz, CDC13) 5 5.86-5.71 (m, 2H), 5.01-4.87 (m,

237

4H), 3.65-3.59 (m, 20H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), l.40-1.20(m, 24H). mp 10.] °C.

rtCzEO7C27t. Isolated by column chromatography (silica gel, ethyl acetate) as a
clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid. Yield 13.2
g (31%). 1H NMR (300 MHz, CDC13) 5 5.87-5.71 (m, 2H), 5.01-4.98 (m, 4H), 3.64-3.60

(m, 24H), 3.59-3.53 (m, 4H), 3.52-3.47 (t, 4H), 2.37-2.28 (m, 4H). mp —5.3 °C.

1tC3EO7C31t. Isolated by column chromatography (silica gel, EtOAc : hexanes =
9 : 1) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 26.8 g (59%). 1H NMR (300 MHz, CDC13) 5 5.85-5.71 (m, 2H), 5.03-4.99 (m,
4H), 3.64-3.58 (m, 24H), 3.57-3.52 (m, 4H), 3.46-3.40 (t, 4H), 2.12-2.03 (m, 4H), 1.70-

1.60 (m, 4H). mp —7.7 °C.

1tC4EO7C41t. Isolated by column chromatography (silica gel, EtOAc : hexanes =
9 : 1) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 16.0 g (49%). 1H NMR (300 MHz, CDC13) 5 586-571 (in, 2H), 5.01-4.87 (m,
4H), 3.65-3.59 (m, 24H), 3.57-3.53 (m, 4H), 3.46-3.40 (t, 4H), 2.09-2.00 (m, 4H), 1.63-

1.52 (m, 4H), 1.47-1.35 (m, 4H). mp —5.4 °C.

nC3EO7C31t. Isolated by column chromatography (silica gel, EtOAc : hexanes =
3 : l) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 28.8 g (49%). 1H NMR (300 MHz, CDCI3) 5 5.86-5.71 (m, 2H), 5.01-4.87 (m,
4H), 3.65-3.59 (m, 24H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), l.40-1.20 (m, 20H). mp 5.9 °C.

238

nCoEO-rColt. Isolated by column chromatography (silica gel, EtOAc : hexanes =
3 : 1) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 30.9 g (50%). 1H NMR (300 MHz, CDC13) 5 5.86-5.71 (m, 2H), 5.01-4.87 (m,
4H), 3.65-3.59 (m, 24H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), 1.40-1.20 (m, 24H). mp 16.0 °C.

nCzEOngn. Isolated by column chromatography (silica gel, EtOAc : MeOH = 9
: l) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 14.0 g (30%). 1H NMR (300 MHz, CDC13) 5 5.87-5.71 (m, 2H), 5.01-4.98 (m,
4H), 3.64-3.60 (m, 28H), 3.59-3.53 (m, 4H), 3.52-3.47 (t, 4H), 2.37-2.28 (m, 4H). mp

1.5 °C.

nC3E03C31c. Isolated by column chromatography (silica gel, EtOAc : MeOH = 9
: l) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 25.9 g (52%). lH NMR (300 MHz, CDC13) 5 5.85-5.71 (m, 2H), 5.03-4.99 (m,
4H), 3.64-3.58 (m, 28H), 3.57-3.52 (m, 4H), 3.46-3.40 (t, 4H), 2.12-2.03 (m, 4H), 1.70-

1.60 (m, 4H). mp -1.1 °C.

7tC4E03C41t. Isolated by column chromatography (silica gel, EtOAc : MeOH = 9
: 1) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 24.3 g (46%). 1H NMR (300 MHz, CDC13) 5 5.86-5.71 (m, 2H), 5.01-4.87 (m,
4H), 3.65-3.59 (m, 28H), 3.57-3.53 (m, 4H), 3.46-3.40 (t, 4H), 2.09-2.00 (m, 4H), 1.63-

1.52 (m, 4H), 1.47-1.35 (m, 4H). mp 0.8 °C.

anEOrngrc. Isolated by column chromatography (silica gel, EtOAc : hexanes =

9 : 1) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.

239

Yield 37.0 g (58%). 1H NMR (300 MHZ, CDCl3) 5 5.86—5.71 (m, 2H), 5.01—4.87 (m,
4H), 3.65-3.59 (m, 28H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), l.40-1.20 (m, 20H). mp 13.2 °C.

nCoEOgCon. Isolated by column chromatography (silica gel, EtOAc : hexanes =
3 : 1) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 37.0 g (56%). 1H NMR (300 MHz, CDC13) 5 5.86—5.71 (m, 2H), 5.01-4.87 (m,
4H), 3.65-3.59 (m, 28H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), 1.40-1.20(m, 24H). mp 17.5 °C.

nCzEOmCzn. Isolated by column chromatography (silica gel, EtOAc : MeOH =
9 : l) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 22.0 g (40%). 1H NMR (300 MHz, CDC13) 5 5.87-5.71 (m, 2H), 5.01-4.98 (m,
4H), 3.64-3.60 (m, 36H), 3.59-3.53 (m, 4H), 3.52-3.47 (t, 4H), 2.37-2.28 (in, 4H). mp

12.6 °C.

nC3EOmC37t. Isolated by column chromatography (silica gel, EtOAc : MeOH =
9 : 1) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.
Yield 28.0 g (48%). 1H NMR (300 MHz, CDC13) 5 5.85-5.71 (m, 2H), 5.03-4.99 (m,
4H), 3.64-3.58 (m, 36H), 3.57-3.52 (m, 4H), 3.46-3.40 (t, 4H), 2.12-2.03 (m, 4H), 1.70-

1.60 (m, 4H). mp 10.7 °C.

nC4E010C47t. Isolated by column chromatography (silica gel, EtOAc : MeOH =
9 : 1) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless liquid.

Yield 31.6 g (52%). 1H NMR (300 MHz, CDCl3) 5 5.86-5.71 (m, 2H), 5.01-4.87 (m,

240

 

 

4H), 3.65-3.59 (m, 36H), 3.57-3.53 (m, 4H), 3.46-3.40 (t, 4H), 2.09-2.00 (m, 4H), 1.63-

1.52 (m, 4H), 1.47-1.35 (m, 4H). mp 12.6 °C.

anEOngn. Isolated by column chromatography (silica gel, EtOAc : Hexanes
= 9 : l) as a clear yellow liquid. Purified by sodium mirror to give a clear colorless
liquid. Yield 34.4 g (48%). 1H NMR (300 MHz, CDC13) 5 5.86-5.71 (m, 2H), 5.01—4.87
(m, 4H), 3.65-3.59 (m, 36H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H),

1.60-1.49 (m, 4H), 1.40-1.20 (m, 20H). mp 19.8 °C.

TcCoEOmColt. Isolated by column chromatography (silica gel, EtOAc : Hexanes
= 9 : 1) as a cloudy yellow liquid. Purified by sodium mirror to give a white crystalline
solid. Yield 42.0 g (56%). 1H NMR (300 MHz, CDC13) 5 5.86—5.71 (m, 2H), 5.01-4.87
(m, 4H), 3.65-3.59 (m, 36H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H),

1.60-l.49 (m, 4H), 1.40-1.20 (m, 24H). mp 24.6 °C.

nC2E014C2n. Isolated by column chromatography (silica gel, EtOAc : MeOH =
9 : l) as a cloudy yellow liquid. Purified by sodium mirror to give a white waxy solid.
Yield 20.5 g (28%). lH NMR (300 MHz, CDCl3) 5 5.87-5.71 (m, 2H), 5.01-4.98 (m,
4H), 3.64—3.60 (m, 52H), 3.59-3.53 (m, 4H), 3.52-3.47 (t, 4H), 2.37-2.28 (m, 4H). mp

23.5 °C.

1tC3E014C31t. Isolated by column chromatography (silica gel, EtOAc : MeOH =
9 : 1) as a cloudy yellow liquid. Purified by sodium mirror to give a white crystalline
solid. Yield 31.6 g (42%). 1H NMR (300 MHz, CDCl3) 5 5.85-5.71 (m, 2H), 5.03-4.99
(m, 4H), 3.64-3.58 (m, 52H), 3.57-3.52 (m, 4H), 3.46-3.40 (t, 4H), 2.12-2.03 (m, 4H),

1.70-1.60 (m, 4H). mp 23.9 °C.

241

 

 

nCaEOMCut. Isolated by column chromatography (silica gel, EtOAc : MeOH =
9 : 1) as a cloudy yellow liquid. Purified by sodium mirror to give a white crystalline
solid. Yield 36.6 g (47%). 1H NMR (300 MHz, CDC13) 5 5.86-5.71 (m, 2H), 5.01—4.87
(m, 4H), 3.65-3.59 (m, 52H), 3.57-3.53 (m, 4H), 3.46-3.40 (t, 4H), 2.09-2.00 (m, 4H),

1.63-1.52 (m, 4H), 1.47-1.35 (m, 4H). mp 22.9 °C.

anEOqult. Isolated by column chromatography (silica gel, EtOAc : MeOH =
95 : 5) as a yellow waxy solid. Purified by sodium mirror to give a white crystalline
solid. Yield 36.8 g (41%). 1H NMR (300 MHz, CDC13) 5 5.86-5.71 (m, 2H), 5.01-4.87
(m, 4H), 3.65-3.59 (m, 52H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H),

1.60-1.49 (m, 4H), 1.40-1.20 (m, 20H). mp 27.7 °C.

7tC9E014C91t. Isolated by column chromatography (silica gel, EtOAc : MeOH =
95 : 5) as a yellow waxy solid. Purified by sodium mirror to give a white crystalline
solid. Yield 39.1 g (43%). 8657] (m, 2H), 5.01-4.87 (m, 4H), 3.65-3.59 (m, 52H),
3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), l.60-1.49 (m, 4H), l.40-1.20 (m,

24H). mp 28.4 °C.

6. Schrock’s Molybdenum Catalyst

Mo(CHCMe2Ph)(NAr)[OCMe(CF3)2]2, Schrock’s molybdenum alkylidene
catalyst was prepared starting from M002, using the five-step synthesis reported in the

literature.

242

 

r1

7. General procedure for the synthesis of ethylene oxide-segmented polymers

Polymer from hexaethylene glycol 0t, (o-di-3-pentenyl ether [(C31tC3E05).,]. In
a helium filled drybox, nC3E05C31t (5.00 g, 12 mmol) was placed in a 30 mL Schlenk
flask with a stir bar. Schrock’s Mo catalyst (15 mg) was added and the mixture was
vigorously stirred at room temperature as ethylene gas evolved from the liquid. The
reaction vessel was removed from the drybox and high vacuum (<0.02 mtorr) was
applied to the system to remove ethylene generated during the polymerization. After 6 h,
the reaction temperature was raised to 50 °C by heating with a silicone oil bath. When
the reaction mixture became too viscous to stir, toluene (10 mL) was added to the
polymer. During the polymerization, the pressure was released occasionally by opening
the reaction to vacuum. The polymerization was terminated after 10 days by exposing it
to air or adding 1 mL of MeOH. Some reactions took longer times to reach the desired
molecular weight. For these cases, a small amount of catalyst (5 mg) was occasionally
added. After termination, 40 mL of toluene was added to dilute the polymerization
solution, the solution was filtered through Celite®, and the polymer was precipitated into
hexanes. The cloudy suspension was centrifuged to separate the precipitate from the
solution. The precipitate was dried in vacuo at 85 °C until constant weight was reached.
The polymer samples were stored in a desiccator at room temperature. Yield 85% of a
yellow tacky gel-like solid (M, = 25,500, PDI = 1.71). 'H NMR (300 MHz, CDC13) 5
5.40-5.38 (m, 2H), 3.65-3.59 (m, 20H), 3.58-3.53 (m, 4H), 3.47-3.41 (t, 4H), 2.13-2.03

(m, 4H), 1.71-1.60 (m, 4H).

(CmCaEOs)... The polymer was purified by precipitation from toluene into

hexanes. Yield 97 % of a yellow tacky gel-like solid (Mn = 48,800, PDI = 1.84). 1H NMR

243

(300 MHz, CDCl3) 5 5.40-5.38 (m, 2H), 3.65-3.59 (m, 20H), 3.57-3.53 (m, 4H), 3.46-

3.40 (t, 4H), 2.09-2.00 (m, 4H), 1.63-1.52 (m, 4H), 1.47-1.35 (m, 4H).

(CglthEOQ... The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into MeOH. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 58,500, PDI =
1.41) in 41% yield. Evaporation of the MeOH solution gave a yellow gel-like solid (Mn
= 15,300, PDI = 1.59) in 43% yield. lH NMR (300 MHz, CDC13) 5 5.40-5.38 (m, 2H),
3.65-3.59 (m, 20H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), l.60-1.49

(m, 4H), 1.40-1.20 (m, 20H).

(ConC9E06)n. The polymer was purified by precipitation from toluene into
hexanes. Yield 89% of a yellow tacky gel-like solid (Mn = 67,800, PDI = 1.56). 1H NMR
(300 MHz, CDC13) 5 5.40-5.38 (m, 2H), 3.65-3.59 (m, 20H), 3.57-3.53 (m, 4H), 3.45-

3.39 (t, 4H), 2.06—1.96 (m, 4H), l.60-l.49 (m, 4H), l.40-l.20 (m, 24H).

(C37tC3EO-r)n. The polymer was purified by precipitation from toluene into
hexanes. Yield 98% of a yellow tacky gel-like solid (Mn = 26,400, PDI = 1.89). 1H NMR
(300 MHz, CDC13) 5 5.40-5.38 (m, 2H), 3.64-3.58 (m, 24H), 3.57-3.52 (m, 4H), 3.46-

3.40 (t, 4H), 2.12-2.03 (m, 4H), 1.70-1.60 (m, 4H).

(C41tC4EO—7)n. The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso-propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 55,500, PDI =
1.79) in 78% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid

(Mn = 25,100, PDI = 2.27) in 20% yield. 1H NMR (300 MHz, CDC13) 5 5.40-5.38 (m,

244

2H), 3.65-3.59 (m, 24H), 3.57-3.53 (m, 4H), 3.46-3.40 (t, 4H), 2.09-2.00 (m, 4H), 1.63-

1.52 (m, 4H), 1.47-1.35 (m, 4H).

(anCgEO-r)n. The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into MeOH. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 58,300, PDI =
1.40) in 44% yield. Evaporation of the MeOH solution gave a yellow gel-like solid (Mn
= 22,300, PDI = 1.47) in 37% yield. 1H NMR (300 MHz, CDC13) 5 5.40-5.38 (m, 2H),
3.65-3.59 (m, 24H), 3.57-3.53 (m, 4H), 345-339 (t, 4H), 2.06-1.96 (m, 4H), 1.60-1.49

(m, 4H), 1.40-1.20 (m, 20H).

(ColtCoEO-r)n. The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into MeOH. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 40,600, PDI =
1.41) in 58% yield. Evaporation of the MeOH solution gave a yellow gel-like solid (Mn
= 11,800, PDI = 1.44) in 27% yield. 1H NMR (300 MHz, CDC13) 5 5.40-5.38 (m, 2H),
3.68-3.59 (m, 24H), 3.58-3.52 (m, 4H), 3.46-3.39 (t, 4H), 2.00-1.90 (m, 4H), 1.60-1.50

(m, 4H), 1.40-1.20 (m, 24H).

(C37tC3E03)... The polymer was purified by precipitation from toluene into
hexanes. Yield 95% of a yellow tacky gel-like solid (Mn = 47,200, PDI = 1.73). 1H NMR
(300 MHz, CDCl3) 5 5.40-5.38 (m, 2H), 3.64-3.58 (m, 28H), 3.57-3.52 (m, 4H), 3.46-

3.40 (t, 4H), 2.12-2.03 (m, 4H), 1.70-1.60 (m, 4H).

(C4RC4E03)0. The polymer was purified by precipitation from toluene into

hexanes. Yield 85% of a yellow tacky gel-like solid (Mn = 19,400, PDI = 1.61). 1H NMR

245

(300 MHz, CDC13) 5 5.40-5.38 (m, 2H), 3.65-3.59 (m, 28H), 3.57-3.53 (m, 4H), 3.46-

3.40 (t, 4H), 2.09-2.00 (m, 4H), 163-1.52 (m, 4H), 1.47-1.35 (m, 4H).

(CgrthEOg)n. The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso-propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 65,700, PDI =
1.46) in 21% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid
(Mn = 30,400, PDI = 1.62) in 73% yield. 1H NMR (300 MHz, CDC13) 5 5.40-5.38 (m,
2H), 3.65-3.59 (m, 28H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), 1.40-1.20 (m, 20H).

(C91'CC9E03)n. The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso-propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 60,100, PDI =
1.51) in 53% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid
(Mn = 23,300, PDI = 1.52) in 38% yield. 1H NMR (300 MHz, CDC13) 5 5.40-5.38 (m,
2H), 3.65-3.59 (m, 28H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

l.49 (m, 4H), l.40-l.20 (m, 24H).

(C31tC3EOro)... The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso-propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 54,500, PDI =
1.57) in 63% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid

(Mn = 14,000, PDI = 2.10) in 34% yield. lH NMR (300 MHz, CDC13) 5 5.40-5.38 (m,

246

2H), 3.64-3.58 (m, 36H), 3.57-3.52 (m, 4H), 3.46-3.40 (t, 4H), 2.12-2.03 (m, 4H), 1.70-

1.60 (m, 4H).

(Can'CaEOm)... The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso-propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 98,500, PDI =
1.38) in 24% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid
(Mn = 28,300, PDI = 2.01) in 71% yield 1H NMR (300 MHz, CDClt) 5 5.40-5.38 (m,
2H), 3.65-3.59 (m, 36H), 3.57-3.53 (m, 4H), 3.46-3.40 (t, 4H), 2.09-2.00 (m, 4H), 1.63-

1.52 (m, 4H), 1.47-1.35 (m, 4H).

(CangEOm)... The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso-propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 41,300, PDI =
1.74) in 29% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid
(Mn = 23,200, PDI = 1.64) in 70% yield. 1H NMR (300 MHz, CDC13) 5 5.40-5.38 (m,
2H), 3.65-3.59 (m, 36H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), 1.40-1.20 (m, 20H).

(ColtCoEOm)n. The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso-propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 52,700, PDI =
1.46) in 28% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid

(Mn = 16,500, PDI = 1.73) in 71% yield. lH NMR (300 MHz, CDC13) 5 5.40-5.38 (m,

247

2H), 3.65-3.59 (m, 36H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), 1.40-1.20 (m, 24H).

(C31tC3E014)n. The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso-propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 17,400, PDI =
2.00) in 46% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid
(Mn = 15,600, PDI = 1.93) in 51% yield. 1H NMR (300 MHz, CDC13) 5 5.40-5.38 (m,
2H), 3.64-3.58 (m, 52H), 3.57-3.52 (m, 4H), 3.46-3.40 (t, 4H), 2.12-2.03 (m, 4H), 1.70-

1.60 (m, 4H).

(C41tC4E014)n. The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso-propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 41,700,.PDI =
1.52) in 58% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid
(Mn = 13,200, PDI = 1.81) in 40% yield. lH NMR (300 MHz, CDC13) 5 5.40-5.38 (m,
2H), 3.65-3.59 (m, 52H), 3.57-3.53 (m, 4H), 3.46-3.40 (t, 4H), 2.09-2.00 (m, 4H), 1.63-

1.52 (m, 4H), 1.47-1.35 (m, 4H).

(anCgE014)n. The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso—propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 21,100, PDI =
1.87) in 57% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid

(Mn = 15,900, PDI = 1.73) in 41% yield. 1H NMR (300 MHz, CDC13) 5 5.40-5.38 (m,

248

2H), 3.65-3.59 (m, 52H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), 1.40-1.20 (m, 20H).

(CortCoEOla)... The polymer was purified by precipitation from toluene into
hexanes. The precipitate was dissolved in THF and re-precipitated into iso-propanol. The
precipitate was dried in vacuo to give a white translucent solid (Mn = 63,200, PDI =
1.64) in 38% yield. Evaporation of the iso-propanol solution gave a yellow gel-like solid
(M, = 59,200, PDI = 1.62) in 59% yield. 1H NMR (300 MHz, CDC13) 5 5.40-5.38 (m,
2H), 3.65-3.59 (m, 52H), 3.57-3.53 (m, 4H), 3.45-3.39 (t, 4H), 2.06-1.96 (m, 4H), 1.60-

1.49 (m, 4H), 1.40-1.20 (m, 24H).

8. General procedure for preparation of saturated polymers.

Preparation of (C10E06)n. A 70 mL Fisher-Porter bottle was charged with
unsaturated polymer (C4RC4E06),, (0.200 g), 20 mL CHzClz, and 0.010 g 10% palladium

on carbon. Hydrogenation was carried out with stirring at room temperature under 5 atm
hydrogen pressure for 2 hours. Upon completion of the reaction, the catalyst (which can
be reused) was filtered and washed with CHzClz. The filtrate was concentrated and the
resulting polymer was dissolved in THF. Precipitation in hexanes followed by drying in
vacuo gave white saturated polymer (C10E06)n (Mn = 11,800, PDI = 1.64) in 97% yield.
1H NMR (300 MHz, CDCl3) 5 3.67-3.58 (m, 20H), 3.57-3.52 (m, 4H), 3.45-3.38 (t, 4H),

1.60-1.49 (m, 4H), 1.34-1.18 (m, 12H).

(C10E07).,. A white waxy solid (Mn = 15,800, PDI = 1.85) prepared by

hydrogenation of polymer (C415C4E06)n in 98% yield. 1H NMR (300 MHz, CDC13) 5

249

3.67-3.58 (m, 24H), 3.57-3.52 (m, 4H), 3.45-3.38 (t, 4H), 1.60-1.49 (m, 4H), 1.34-1.18

(m, 12H).

(C10E03)n. A white waxy solid (Mn = 13,200, PDI = 1.98) prepared by
hydrogenation of polymer (C4RC4E06)n in 98% yield. lH NMR (300 MHz, CDC13) 5
3.67-3.58 (m, 28H), 3.57-3.52 (m, 4H), 3.45-3.38 (t, 4H), 1.60-1.49 (m, 4H), 1.34-1.18

(m, 12H).

(CroEOw),,. A white waxy solid (Mn = 24,100, PDI = 2.41) prepared by
hydrogenation of polymer (CanC4E06)n in 99% yield. 'H NMR (300 MHz, CDC13) 5
3.67-3.58 (m, 36H), 3.57-3.52 (m, 4H), 3.45-3.38 (t, 4H), 1.60-1.49 (m, 4H), 134-1.18

(m, 12H).

(C10E014),,. A white waxy solid (Mn = 8,500, PDI = 1.58) prepared by
hydrogenation of polymer (C4nC4EO6)n in 99% yield. 1H NMR (300 MHz, CDC13) 5
3.67-3.58 (m, 52H), 3.57-3.52 (m, 4H), 3.45-3.38 (t, 4H), 1.60-1.49 (m, 4H), 1.34-1.18

(m, 12H).

(C20E07)... A white waxy solid (Mn = 9,900, PDI = 1.45) prepared by
hydrogenation of polymer (C41tC4E06)n in 99% yield. 1H NMR (300 MHz, CDCI3) 5
3.67-3.58 (m, 24H), 3.57-3.52 (m, 4H), 3.45-3.38 (t, 4H), 1.60-1.49 (m, 4H), 1.34-1.18

(m, 32H).

250

III.

Number of Compounds
H(OCH2CH2)yOH
1(y)
Ts(OCH2CH2)yOTs
2(y)
Tr((OCH2CH2)yOH
3U)
Tr(OCH2CH2)yOTr
4(y)
H(CH2)X(0CH2CH2)yO(CH2)xH
CxEOyC,‘
CH2=CH(CH2)x (OCH2CH2)yO(CH2)xCH=CH2
anEOnylt
[(CH2)x CH=CH(CH2)x (OCHZCH2)y]n
(CranEOy)n
[(CH2)x(0CH2CH2)y]n

(CxEOy)n

251

APPENDIX

252

 

ClGEOZClfi

 

Heat flow, Endo ———>

 

 

C14E02014 1

 

 

012150th2 J L

 

C10E02010

 

 

08150208 A

 

 

l 4 l l l

 

-40 -20 0 20 40
Temperature (°C)

Figure 89. DSC heating scans of triblock oligomers CxEOzCx

253

 

Heat flow, Endo ———p

 

CrsEOaCte

 

C14E03014

 

 

C12E03012

 

 

 

 

010503010

CgEO3Cg

 

 

1

 

Figure 90. DSC heating scans of triblock oligomers CxEOgCx

10
Temperature (°C)

254

30

50

 

 

Heat flow, Endo _,

 

016E04016

 

C14EO4014

 

C12504012

 

 

 

 

 

C10504010

 

CBEO4CB

 

 

Figure 91. DSC heating scans of triblock oligomers c,eo.c,

 

l l

O 20
Temperature (°C)

255

40

 

60

Heat flow, Endo ——__p

 

C16EOSC16

 

CMEOSCM

 

C12EC)5012

 

 

C10E05010

J1

 

08150508

 

 

 

 

 

Jl

 

1 1

 

 

Figure 92. DSC heating scans of triblock oligomers CxEOgCx

0 20
Temperature (°C)

256

40

60

 

 

 

016150.01. J
Caeoacr. . J]

 

 

 

 

C12E06012

 

 

Heat flow, Endo ——-—>

 

 

ClOEOBClo J

 

 

 

 

1 l l A

 

-20 O 20 40 60
Temperature (°C)

Figure 93. DSC heating scans of triblock oligomers CREOgCx

257

 

C16EOBC16 A

 

 

 

014E08C14 L

 

 

C12E08C12

cioeorcro A

(3815080.3 A

 

 

Heat flow, Endo

 

 

 

 

 

 

 

0.508%

-1 0 0 1 O 20 30 40 50 60
Temperature (°C)

1 l l 1

 

Figure 94. DSC heating scans of triblock oligomers chOQCx

258

 

C16E010016 J

 

 

Cr4E016014

 

 

Heat flow, Endo

 

 

C10E010C10

 

 

CgEOng

 

 

CBEO1OC6

J
11
A

11

 

 

 

1 l

 

-1 0 0 1 0 20 30 40 50

Temperature (°C)

Figure 95. DSC heating scans of triblock oligomers C,Eo,oc,

259

 

Heat Flow, Endo ————~>

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

016E014C16 A
014501.01. A
C125014012 A
C105014010
0.50.40. L
0,150,406 1

0 10 20 30 40 50

Temperature (°C)

60

Figure 96. DSC heating scans of triblock oligomers CXEOmCx

260

heat flow, endo

 

hold at 10 °C

 

hold at 0 °C

 

hold at -10 °C

/\
M

 

 

 

fast cooled

 

 

 

room temp. obtained

1 l l f l l I

-20 -10 O 10 20 30 40 50
temperature (°C)

 

 

 

Figure 97. DSC heating scans of polymer (C47tC4E05),, with
different crystallization histories.

261

 

hold at 10 °C

 

hold at 0 °C

 

hold at ~10 °C

 

 

 

heat flow, endo

fast cooled

 

.11
/1/
JV

room temp. obtained

 

/

l l l l l l

 

 

 

-20 -1 0 0 1 0 20 30 40
temperature (°C)

Figure 98. DSC heating scans of polymer (C41tC4EO-,),, with
different crystallization histories.

262

heat flow, endo ——>

 

hold at 17 °C

 

hold at 7 °C

 

hold at 2 °C

 

 

slow cooled

 

fast cooled

 

/\
A
is
A
A

room temp. obtained

 

 

 

temperature (°C)

40 50

Figure 99. DSC heating scans of polymer (C47tC4EOg),, with

different crystallization histories.

263

 

 

hold at 16 °C

 

hold at 0 °C

 

slow cooled

 

heat flow, endo ———>

fast cooled

 

room temp. obtained

 

 

. / .

 

 

0 1O 20 30
temperature (°C)

40 50

Figure 100. DSC heating scans of polymer (C41IC4EO1O)., with

different crystallization histories.

264

heat flow, endo ——>

 

hold at 28 °C

hold at 18 °C

hold at 0 °C

/

slow cooled

fast cooled

 

 

 

 

 

 

 

 

 

Figure 101. DSC heating scans of polymer (C4TCC4EO14),, with

temperature (°C)

different crystallization histories.

265

50

 

heat flow, endo

 

 

 

 

 

 

 

 

 

 

 

 

/\v hold at 40 °C ‘
/\ hold at 35 °c
I/w/Ak hold at 30 °c
M hold at 22 °C
H hold at 16 °c
flrfl hold at 10 °C
W hold at 0 °C
\v A slow cooled
fast cooled

 

 

 

M

room temp. obtained

 

 

J I

 

20 40
temperature (°C)

60

Figure 102. DSC heating scans of polymer (Cr,rl:CgE06)n with

different crystallization histories.

266

heat flow, endo ——>

 

hold at 25 °C

 

1

hold at 17 °C

 

hold at 6 °C

 

W

 

slow cooled

 

 

 

fast cooled

 

room temp. obtained

 

M
M
A

 

20 40
temperature (°C)

60

Figure 103. DSC heating scans of polymer (CancgEO7),, with

different crystallization histories.

267

 

 

heat flow, endo

 

hold at 43 °c /—

hold at 30 °(

‘1

 

hold at 20 °C

 

hold at 15 °C

 

 

 

hold at 0 °C

slow cooled

 

 

 

fast cooled

 

room temp. obtained

 

/\
//\
A
A
A
./\.

l

 

 

1O 20 30
temperature (°C)

40

Figure 104. DSC heating scans of polymer (anCgE03)n with

different crystallization histories.

268

50

 

heat flow, endo

 

hold at 23 °C

 

 

 

 

 

 

 

/"
hold at 15 °C /\
hold at 0 °C A

f’* f
slow cooled A
fast cooled M

 

room temp. obtained

 

 

I l l J 1

 

 

0
0'1

temperature (°C)

Figure 105. DSC heating scans of polymer (CancaEOm)n with
different crystallization histories.

269

10 15 20 25 3O 35 4O 45

50

 

heat flow, endo

 

hold at 30 °C

hold at 19 °C

hold at 0 °C

 

 

 

slow cooled

 

 

fast cooled

 

 

room temp. obtained

 

/\
/\
/\
A
A
0/{\

 

 

 

temperature (°C)

Figure 106. DSC heating scans of polymer (CancaEO14),, with
different crystallization histories.

270

50

heat flow, endo ———>

 

hold at 36 °c /”’"\

hold at 32 °C

 

hold at 22 °C M

 

 

hold at 0 °

 

 

/

hold at 15 ° W

slow cooled

S

 

fast cooled

 

 

room temp. obtained A

 

 

r 1 l

 

0 20 40 60

temperature (°C)

Figure 107. DSC heating scans of polymer (C§,11.'C9EO¢;)n with
different crystallization histories.

271

 

 

heat flow, endo

ll 5%:

 

hold at 40 °C

 

hold at 20 °C

 

hold at 10 °C

 

hold at 0 °C

 

 

 

slow cooled

 

 

fast cooled

 

room temp. obtained

 

 

 

I l

 

O 20 4O 60

temperature (°C)

Figure 108. DSC heating scans of polymer (09nC9E07)n with
different crystallization histories.

272

 

 

heat flow, endo

 

/\ hold at 35 °c

hold at 32 °C

 

hold at 25 °C

 

hold at 20 °C

 

 

slow cooled

 

 

fast cooled

 

 

 

/\
/\
m
M m... 10°C
[A
4.——/\
A

room temp. obtained

 

 

l l l

 

0 20 4O 60

temperature (°C)

Figure 109. DSC heating scans of polymer (ancgE03)n with
different crystallization histories.

273

 

 

 

heat flow, endo

 

hold at 33 °C /’"'" M

 

hold at 30 °C /

 

hold at 26 °C /\

 

 

hold at 20 °C /\——/\

hold at 0 °C

 

 

/_____,

A
slow cooled A
,/\

fast cooled

 

 

 

room temp. obtained N

 

 

O 1 O 20 30 4O
temperature (°C)

Figure 110. DSC heating scans of polymer (C9KC9E010),, with
different crystallization histories.

heat flow, endo —>

 

hold at 25 °C

hold at 20 °C for 16 h

hold at 0 °C
f

slow cooled

fast cooled

room temp. obtained

 

1

 

A

 

 

l l

 

 

0 10

Figure 111. DSC heating scans of polymer (091tC9EO14)n with

20 3O
temperature (°C)

different crystallization histories.

275

40

50

 

 

hold at 40 °C

 

 

hold at 20 °C M

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0 hold at 0 °C

2 Ff

G)

3'

..—‘3

*5

0)

.2
slow cooled fir”
fast cooled /V/\
room temp. obtained /\

r
0 20 40 60

temperature (°C)

Figure 112. DSC heating scans of polymer (GREG-0,, with different
crystallization histories.

276

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