SYNTHESIS OF POLY(IONIC LIQUIDS) BOTH IN SOLUTION AND ON
SURFACE OF SILICA NANOPARTICLES AS NOVEL QUASI-SOLID STATE
ELECTROLYTES
By
Heyi Hu

A DISSERTATION
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
Chemistry - Doctor of Philosophy
2013

ABSTRACT
SYNTHESIS OF POLY(IONIC LIQUIDS) BOTH IN SOLUTION AND ON
SURFACE OF SILICA NANOPARTICLES AS NOVEL QUASI-SOLID STATE
ELECTROLYTES
By
Heyi Hu
Ionic liquids (ILs) are compounds composed of cations and anions with
low melting point, usually below room temperature. ILs have some unique
properties, such as high intrinsic ionic conductivity, non-volatility, nonflammability, thermal and chemical stability. Based on these properties, ILs have
been considered as promising electrolyte materials. However, the sealing and
fabrication of IL electrolytes remained a challenge in industry applications due to
their liquid property. One way to solve this problem was to polymerize the ILs.
Compared to ILs, poly(ionic liquids) (PILs) have enhanced mechanical stability,
improved processability and durability. However, PILs have their own drawback,
which is that once polymerized, the ionic conductivity of PILs drops a lot, usually
several orders of magnitude lower than that of their monomers. To successfully
apply PILs as electrolyte materials, the ionic conductivity must be improved.
To have high conductivity, the PILs synthesized must have low Tgs. A
series of low Tg polymer polyepichlorohydrin (polyEPCH) with molecular weight
ranging from 22,000 to 76,000 were synthesized by anionic ring-opening
polymerization. After quaternarization and ion exchange, a novel family of PIL
electrolytes were synthesized and characterized. The PILs obtained showed not

only low Tg, high conductivity and good thermal stability, but also a high viscosity,
which is beneficial in fabricating process.
To get even higher conductivity, another low Tg monomer, 2-((2-(2-(2methoxyethoxy)ethoxy)ethoxy)methyl)oxirane (ME3MO), was synthesized and
randomly copolymerized with EPCH by cationic ring-opening polymerization. The
resulting copolymer (polyEPCH-co-polyME3MO) was quaternarized and ion
exchanged to form a PIL copolymer (polyGBIMTFSI-co-polyME3MO). By tuning
the monomer composition, a series of PIL copolymers from polyGBIMTFSI-copolyME3MO-8/1 to polyGBIMTFSI-co-polyME3MO-1/4 were synthesized. All PIL
copolymer samples showed higher ionic conductivity than PIL homopolymer.
Among them, polyGBIMTFSI-co-polyME3MO-1/1 showed the highest ionic
-4

conductivity (around 1.2 x 10

S/cm at 25 oC), which was more than 1 order of

magnitude higher than PIL homopolymer (9.3 x 10

-6

S/cm at 25 oC).

We also synthesized PILs on the surface of silica nanoparticles via
surface initiated atom transfer radical polymerization (ATRP). A gel electrolyte
was formed by dispersing the PIL/silica nanocomposites in 1-methyl-3propylimidazolium iodide and heating for 1 h. The gel electrolyte was used as a
quasi-solid state electrolyte in DSSC and a 0.37 % conversion efficiency was
achieved.

To My Beloved Family

iv

ACKNOWLEDGMENTS

I would like to sincerely thank my advisor, Professor Gregory L. Baker for
his guidance, assistance and patience during my graduate study at Michigan
State University. I would like to express my deep gratitude to all my committee
members, Dr. Xuefei Huang, Dr. Merlin Bruening, Dr. Kevin Walker and Dr.
Milton Smith, for their guidance and helpful suggestions.
I would like to thank all past and present Baker group members: Qin,
Sampa, Hui, Gina, Wen, Quanxuan, Yiding, Zhe, Greg and Salinda. I would like
to thank Dan Holmes, Kathy Severin and Mike Rich for their help on various
instruments.
Finally, I would like to thank my family for always supporting me and my
girl friend, Qingmei, for her love.

v

TABLE OF CONTENTS
LIST OF TABLES .............................................................................................. ix
LIST OF FIGURES ............................................................................................ .x
LIST OF SCHEMES ....................................................................................... .xiii
Chapter 1. Introduction ..................................................................................... 1
Ionic liquids............................... ........................................................................ 1
Histroy and formation of ILs ............................................................................ 1
Application of ILs ............................................................................................ 3
ILs used as green alternatives to volatile organic solvents .......................... 4
ILs used as absorbents of CO2 ................................................................... 5
ILs as electrolyte .......................................................................................... 9
ILs in lithium batteries.................................................................................9
ILs in fuel cells ......................................................................................... 12
ILs in DSSCs ........................................................................................... 14
Poly(ionic liquids) (PILs) .................................................................................. 16
Formation of PILs ......................................................................................... 16
PILs composed of polycations and free anions .......................................... 17
PILs composed of polyanions and free cations .......................................... 18
Zwitterionic PILs ......................................................................................... 19
Synthesis of PILs.............................................................................................20
Direct polymerization of IL monomers..........................................................20
Chemical modification of existing polymers..................................................21
Application of PILs..........................................................................................23
Factors affecting ionic conductivity of PILs...................................................23
Anion effect on ionic conductivity of PILs...................................................23
Effect of spacer structure and length on ionic conductivity of
PILs.............................................................................................26
Effect of alkyl chains on imidazolium ring on ionic conductivity
of PILs.........................................................................................29
Effect of cation structures of ionic conductivity of PILs..............................30
Effect of immobilizing anions on the backbone with free cations
on ionic conductivity of PILs........................................................32
Effect of degree of polymerization on ionic conductivity of PILs................35
Effect of crosslinking on ionic conductivity of PILs.....................................36
Effect of copolymer on the conductivity of PILs.........................................43
REFERENCES .................................................................................................. .51
Chapter 2. Synthesis and characterization of novel low Tg PILs ....................... 64
Introduction..........................................................................................................64
Results and discussion ...................................................................................... 69
Synthesis of polyepichlorohydrin based PILs ................................................ 69

vi

Thermal analysis of polyEPCH and polyGBIMTFSI samples ........................ 81
Ionic conductivity and viscosity measurement.................................................84
Conclusion...........................................................................................................87
Experimental section............................................................................................88
Materials..........................................................................................................88
Synthesis of polyEPCH with monomer to initiator molar ratio from 100 to
500...................................................................................................................88
Synthesis of poly(1-glycidyl-3-butylimidazolium chloride) (polyGBIMCl).........89
Synthesis of poly(1- glycidyl-3-butylimidazolium
bis(trifluoromethanesulfonyl)imide) (polyGBIMTFSI).......................................90
Characterization...................................................................................................91
Ionic conductivity measurements.........................................................................92
REFERENCES....................................................................................................94
Chapter 3. Synthesis and characterization of novel low Tg PILs random
copolymers..................................................................................... 98
Introduction..........................................................................................................98
Results and discussion......................................................................................100
Synthesis of polyGBIMTFSI-co-polyME3MO.................................................100
Thermal analysis of polyGBIMTFSI-co-polyME3MO samples.......................111
Conclusion.........................................................................................................115
Experimental section..........................................................................................117
Materials........................................................................................................117
Synthesis of ME3MO.....................................................................................117
Synthesis of polyEPCH by cationic ring-opening polymerization...................118
Synthesis of polyME3MO...............................................................................119
Synthesis of polyEPCH-co-polyME3MO random copolymer.........................120
Synthesis of poly GBIMTFSI-co-polyME3MO................................................121
Characterization.................................................................................................121
Ionic conductivity measurements.......................................................................122
REFERENCES..................................................................................................125
Chapter 4. Direct polymerization of IL monomers from surface of silica
nanoparticles: kinetics, characterization, and application in
DSSCs...........................................................................................126
Introduction........................................................................................................126
Results and discussion......................................................................................128
Synthesis of VBBIT........................................................................................128
Surface-initiated ATRP of VBBIT from silica nanoparticles...........................137
Application as novel quasi-solid state electrolyte in DSSCs.........................145
Conclusion.........................................................................................................148
Experimental section..........................................................................................149
Materials........................................................................................................149
Synthesis of VBBIT........................................................................................149

vii

Synthesis of ATRP initiator modified silica nanoparticles..............................150
Synthesis of polyVBBIT/silica nanocomposites.............................................152
Characterization.................................................................................................152
Calculation of initiator content on the surface of silica nanoparticles.................153
Kinetic study.......................................................................................................154
DSSC fabrication...............................................................................................154
REFERENCES..................................................................................................157
APPENDIX.........................................................................................................162

viii

LIST OF TABLES

Table 1.1.

Tg of macromonomers and PILs .................................................. 25

Table 2.1.

Polymerization of epichlorohydrin initiated by NOct4Br / iBu3Al ............................................................................................ 71

Table 2.2.

Number average molecular weight (Mn), Weight average
molecular weight (Mw) and PDI of polyEPCH 100 , 200 and
500 from GPC, PS as standard .................................................... 78

Table 2.3.

Number average molecular weight (Mn), Weight average
molecular weight (Mw) and PDI of polyEPCH 100 , 200 and
500 from GPC, PEO as standard ................................................. 79

Table 2.4.

Tg of polyEPCH and polyGBIMTFSI with different monomer
to initiator ratio.............................................................................. 83

Table 3.1.

Molecular weight of polyEPCH synthesized using different iBu3Al/NOct4Br ratio ..................................................................... 106

Table 3.2.

Molecular weight of polyME3MO synthesized using different
i-Bu3Al/NOct4Br ratio ................................................................... 107

Table 3.3.

Molecular weight of polyEPCH, polyME3MO and polyEPCHco-polyME3MO synthesized using BF3OEt2 and 1,4butanediol as initiator ................................................................... 109

Table 3.4.

Tg of the polyGBIMTFSI, polyME3MO and their random
copolymers with varying molar composition ................................. 113

Table 4.1.

Short circuit current density (Jsc), open circuit voltage (Voc),
fill factor (ff) and conversion efficiency of DSSCs with
PMII/polyVBBIT/silica nanocomposites gel electrolyte ................. 147

ix

LIST OF FIGURES

Figure 1.1.

Temperature dependence of the ionic conductivity of
macromonomers ( ● ,X = TFSI; ▲ , X = Cl) and their
corresponding polymers (○, X = TFSI, △, X = Cl). ..................... 26

Figure 1.2.

Effect of spacer structure and length on the ionic conductivity
for PILs ......................................................................................... 29

Figure 1.3.

Effect of alkyl chain on the ionic conductivity and Tg for
macromonomer 1, 3, 4 and their corresponding PILs. ................. 30

Figure 1.4.

Conductivities of PILs with different cation structures .................. 32

Figure 1.5.

Temperature dependence of the ionic conductivity for
EImVS, EImC3S, and their polymers. ( ○ ) EImVS, ( ● )
P(EImVS), ( △ ) EImC3S, ( ▲ ) P(EImC3S). P implies
polymerized system. .................................................................... 35

Figure 1.6.

The photograph of film electrolyte composed of PIL and 3
mol% E3V cross-linker. ................................................................ 38

Figure 1.7.

The effect of cross-linker (E3V) concentration on the ionic
conductivity and Tg of the PIL film................................................ 40

Figure 1.8.

Temperature dependence of the ionic conductivity for PIL
films with different cross-linkers(x = 2 or 3). ................................. 41

Figure 1.9.

Temperature dependence of the ionic conductivity for PIL
films with different cross-linkers(y = 4 or 13-14). .......................... 42

Figure 1.10. Temperature dependence of the ionic conductivity for PIL
films with different cross-linkers(z = 2 or 9). ................................. 43
Figure 1.11. Temperature dependence of ionic conductivity for poly(HMAco-MEBIm-BF4)............................................................................ 46
Figure 1.12. Composition and glass transition dependence of ionic
conductivity for poly(HMA-co-MEBIm-BF4). ................................. 47

x

Figure 1.13. Temperature dependence of ionic conductivity for
poly(MEBIm-TFSI-co-MEBIm-BF4) .............................................. 48
Figure 1.13. Composition and glass transition dependence of ionic
conductivity for poly(MEBIm-TFSI-co-MEBIm-BF4) ..................... 49
Figure 2.1.

1

H NMR of polyEPCH with monomer to initiator ratio 500/1

(2.1a, top, CDCl3 as solvent) and the corresponding
polyGBIMTFSI (2.1b, bottom, DMSO-d6 as solvent). .................. 74
Figure 2.2.

gHSQC of polyEPCH with monomer to initiator ratio 500/1 ......... 75

Figure 2.3.

gHSQC of polyGBIMTFSI with monomer to initiator ratio
500/1 ............................................................................................ 76

Figure 2.4.

GPC traces of polyEPCH with different monomer to initiator
ratio. PolyEPCH 100, 200, 500 means polyEPCH with [M]/[I]
= 100, 200 and 500 respectively. DMF was used as solvent
at 50 oC and polystyrene was used as standard .......................... 78

Figure 2.5.

FT-IR of LiTFSI, butylimidazole, polyEPCH 500 and the
corresponding polyGBIMTFSI500. ............................................... 80

Figure 2.6.

Normalized TGA traces of polyEPCH with [M]/[I] 500 and the
corresponding polyGBIMTFSI ...................................................... 81

Figure 2.7.

DSC curves of polyEPCH100, 200 and 500 and the
corresponding polyGBIMTFSI. From top to bottome, curves
are for polyEPCH100, 200, 500 and polyGBIMTFSI100, 200,
500 respectively.. ......................................................................... 83

Figure 2.8.

Temperature dependence of ionic conductivities for
polyGBIMTFSI 100, 200 and 500.. ............................................... 85

Figure 2.9.

Temperature dependence of viscosities of polyGBIMTFSI
100, 200 and 500.. ....................................................................... 86

Figure 3.1.

1

H NMR of ME3MO ...................................................................... 102

Figure 3.2.

gHSQC of ME3MO ....................................................................... 103

Figure 3.3.

gHMBC of ME3MO ....................................................................... 104

xi

Figure 3.4.

1

H NMR of polyGBIMTFSI-co-polyME3MO-4/1 ........................... 110

Figure 3.5.

TGA traces of polyGBIMTFSI, polyME3MO and their random
copolymer with varying molar composition. .................................. 112

Figure 3.6.

Ionic conductivities of polyGBIMTFSI and its random
copolymers with varying molar composition. ................................ 115

Figure 4.1.

1

H NMR of VBBIT, DMSO-d6 as solvent ..................................... 130

Figure 4.2.

FT-IR spectra of (a) silica nanoparticles, (b) surface initiator,
(c) polyVBBIT/silica nanocomposite, and (d) polyVBBIT
homopolymer. Samples were made into pellets with KBr ............ 133

Figure 4.3.

TGA data for (a) silica nanoparticles, (b) nanoparticles
modified
with
surface
anchored
initiators,
(c)
polyVBBIT/silica nanocomposites (d) and polyVBBIT. All
samples were run in air and at a heating rate of 10 °C/min.......... 134

Figure 4.4.

500 MHz H NMR spectra of a representative sample for
kinetic study of surface initiated ATRP of VBBIT ......................... 136

Figure 4.5.

Kinetic study of surface initiated ATRP of VBBIT, the
concentration ratio of [M]0 : [Si-Ini] : [CuBr] : [PMDETA] is

1

approximately 100 : 1 : 2 : 6. [M]0 and [M] represent the
initial concentration of VBBIT monomer and the
concentration of monomer at specific time ................................... 137
Figure 4.6.

TEM images of dried Snowtex-XS nanoparticles (a, top), and
polyVBBIT/silica nanocomposites (b, bottom) .............................. 139

Figure 4.7.

DSC
curves
of
polyVBBIT
homopolymer
and
polyVBBIT/silica nanocomposites ................................................ 141

Figure 4.8.

Conductivity of pure PMII and PMII with different amount of
polyVBBIT/silica nanocomposites ................................................ 143

Figure 4.9.

J-V curve of the DSSC with PMII/polyVBBIT/silica
nanocomposites gel electrolyte .................................................... 146

Figure A1.

Ideal Nyquist plot of Scheme A1 .................................................. 164

xii

Figure A2.

Example of a typical Nyquist plot obtained from AC
impedance measurement. (Sample is polyGBIMTFSI-copolyME3MO-1/1 at 90 oC.) ........................................................... 165

xiii

LIST OF SCHEMES

Scheme 1.1. Structures of most commonly used cations and anions in ILs ...... 3
Scheme 1.2. Diels-Alder cycloaddition of cyclopentadiene with methyl
acrylate or methyl vinyl ketone in IL ............................................. 4
Scheme 1.3. Synthesis of polyimide by polycondensation reaction in IL .......... 5
Scheme 1.4. Carbamte mechanism for CO2 capature using aqueous
amine solutions ............................................................................ 6
Scheme 1.5. Reaction between CO2 and 1-ethyl-3-methyl-imidazolium
acetate via a carbene mechanism................................................ 8
Scheme 1.6. Two examples of reaction schematics between CO2 and IL
with amine group in its counter anion ........................................... 9
Scheme 1.7. Structures of the most common polycationic PILs........................ 17
Scheme 1.8. Structures of PILs with polyanions and free cations ..................... 18
Scheme 1.9. Polyanionic PILs with trifluoromethanesulfonamide anion
(left) and cations other than imidazolium like
tetraalkylammonium cations (right) ............................................. 19
Scheme 1.10. Zwitterionic PILs reported in literature ....................................... 20
Scheme 1.11. General synthetic route to PILs from methacryloyl IL
monomers bearing imidazolium species. (R: alkyl chain; X:
halide) .......................................................................................... 21
Scheme 1.12. Synthesis of poly(1-butyl-3-vinylbenzylimidazolium
chloride) by post-polymerization modification of poly(pchloromethylstyrene). ................................................................... 22
Scheme 1.13. Synthetic route to PS-b-PMVBI block copolymers via postpolymerization of a preformed diblock copolymer ........................ 23
Scheme 1.14. Structure of macromonomer (X = Cl or TFSI). ........................... 25

xiv

Scheme 1.15. Structures of macromonomers based on (meth)acryloyl
groups .......................................................................................... 28
Scheme 1.16. Monomers with different cation structures ................................. 31
Scheme 1.17. Structures of IL monomers with immobilizing anions and
free imidazolium cations ............................................................... 33
Scheme 1.18. Synthesis of IL monomer with alkyl spacer between vinyl
group and sulfonate ..................................................................... 34
Scheme 1.19. Monomer with vinyl imidazolium cation and vinyl sulfonate
anion ............................................................................................ 36
Scheme 1.20. Structure of acrylate based PIL with six repeating
methylene units as the spacer ..................................................... 37
Scheme 1.21. Structures of cross-linkers used ................................................ 37
Scheme 1.22. Structures of Nonionic-Ionic random copolymer and IonicIonic random copolymer ............................................................... 45
Scheme 2.1. ACE and AM mechanism for cationic ring-opening
polymerization of epichlorohydrin ................................................. 67
Scheme 2.2. Mechanism for NOct4Br, i-Bu3Al initiated anionic
polymerization of epichlorohydrin ................................................. 68
Scheme 2.3. Synthesis of polyEPCH and polyGBIMTFSI ................................. 71
Scheme 3.1. Mechanism for trifluoroborate etherate and 1,4-butanediol
initiated cationic polymerization of epichlorohydrin ...................... 99
Scheme 3.2. Synthesis of ME3MO.................................................................... 101
Scheme 3.3. Copolymerization of EPCH and ME3MO, followed by
quaternatization............................................................................ 108
Scheme 4.1. Synthesis of IL monomer-VBBIT .................................................. 129
Scheme 4.2. Synthetic route to polyVBBIT/silica nanocomposites. .................. 132
Scheme 4.3. Pictures of polyVBBIT/silica nanocomposites, PMII and their
mixture ......................................................................................... 142
xv

Scheme 4.4. Gels formed after conductivity measurement from 25 °C to
90 °C. PMII with 20 wt% polyVBBIT/silica nanocomposites
(a) and PMII with 15 wt% polyVBBIT/silica nanocomposites.
(b)................................................................................................. 144
Scheme A1. Equivalent circuit of the electrochemical response of the cell
used in conductivity measurement ............................................... 163

xvi

Chapter 1 Introduction
Ionic liquids.
Ionic liquids (ILs), also called molten salts, are compounds composed of cations
and anions with low melting point, usually below 100 °C. Room temperature ILs,
more specifically, are ILs existing in liquid state at room temperature.
History and formation of ILs.
IL was first synthesized in 1914 by Paul Walden,

1

who reported that by

neutralizing ethylamine with concentrated nitric acid, a salt, ethylammonium
nitrate with melting point 13 - 14 °C was obtained. However, though his discovery
was now widely accepted as the starting point of IL study, this paper did not
attract much attention at that time. It was not until 1975 that a real breakthrough
2

in IL research was made by Osteryoung group, in which he studied detailed
physical properties of 1-butylpyridium chloride and aluminium(III) chloride, the
[C4py]Cl-AlCl3 system and found that between 60 to 67 mol% of AlCl3, this
system was in liquid state at room temperature (melting point below 20 °C).
However, one serious limitation of this system was its narrow liquid range. In
3

1982, Wilkes and Hussey

developed a new system based on 1-ethyl-3-

methylimidazolium chloride and aluminium(III) chloride, [C2mim]Cl-AlCl3, which
showed a much wider liquid range from ~ 30 to 60 mol% of AlCl3. The biggest
problem related to this kind of AlCl3 based ionic liquid system was that it was
1 
 

moisture sensitive, which would be decomposed even when trace amount of
water existed. Due to this problem, synthesis and use of AlCl3 based ionic liquid
system was limited in glove box or other devices filled with inert gas. The first IL
which could be synthesized and used on bench was discovered by Wilkes and
4

Zaworotko in 1992. The new non-(moisture sensitive) IL still contained a 1-ethyl3-methylimidazolium ([C2mim]) cation, but with different anions, such as nitrate
-

-

-

(NO3 ), tetrafluoroborate (BF4 ) and acetate (CH3CO2 ). However, Wilkes and
Zaworotko's IL still needed to be used under inert atmosphere. Though they did
not react with water, they would absorb quite a lot of moisture from the air. To
5

solve this problem, Grätzel and coworkers prepared more hydrophobic anions,
such as

-

-

trifluoromethanesulfonate ([CF3SO3 ]), trifluoroacetate ([CF3CO2 ]),
-

bis(trifluoromethanesulfonyl)imide ([N(CF3SO2)2 ]) and heptafluorobutanoate
-

([C3F7CO2 ]). Since then, more and more papers studying ILs were published.
Common

cations

in

ILs

include

imidazolium,

tetraalkylammonium,

tetraalkylphosphonium, pyridinium, and pyrrolidinium. Common anions include
chloride,

bromide,

bis(trifluoromethanesulfonyl)imide

tetrafluoroborate,

hexafluoroborate,

and dicyanamide. Among them, imidazolium

based ILs were the most popular. Scheme 1.1 shows the structures of most
commonly used cations and anions in ILs.

2 
 

6

Scheme 1.1. Structures of most commonly used cations and anions in ILs.

Application of ILs
Currently, ILs have been used in a lot of areas, such as electrolytes in
7

8

electrochemical devices, absorbents of CO2, catalysts in organic synthesis and
polymerization,
chemistry.

9

green solvents,

10,11

and separation reagents in analytical

12

3 
 

ILs used as green alternatives to volatile organic solvents
One simple and qualitative definition for polar solvent is that a polar solvent can
dissolve and stabilize polar or charged solutes. Under this definition, ILs are
generally considered as highly polar solvents.

13

Due to their good solubility to

many organic and inorganic compounds, negligible volatility, chemical and
thermal stability, ILs were used to replace traditional organic solvents in organic
synthesis and polymerization in the past two decades. A lot of organic synthesis
14,15

has been conducted in IL solvent, such as substitution,
addition reactions.

18,19

elimination,

16,17

and

Among all of these reactions, Diels-Alder cycloaddition

was one of the first to be studied. Scheme 1.2 shows the Diels-Alder reaction of
cyclopentadiene with methyl acrylate or methyl vinyl ketone.

19

Compared to non-

polar organic solvents, IL ethylammonium nitrate (mp ~ 12 °C) showed
enhancement of endo stereoselectivity.

Scheme 1.2. Diels-Alder cycloaddition of cyclopentadiene with methyl arylate or
methyl vinyl ketone in IL.

4 
 

Polymerizations such as polycondensation,
and anionic)

22,23

20,21

ionic polymerization (cationic
24-26

and radical polymerization (free radical, ATRP and RAFT)

have also been conducted in ILs. Compared to traditional organic solvents, ILs
have two main advantages. The first is that their thermal stability and nonvolatility enable high temperature polymerization such as polycondensation
reaction. The second is that their abilitites to dissolve inorganic or organometallic
catalysts enable homogeneous polymerization, which sometimes is impossible
27

with organic solvents.

Scheme 1.3 shows an example of polycondensation

reaction between aromatic dianhydride and diamine to form polyimide.

21

Quantitative yield was obtained.

Scheme 1.3. Synthesis of polyimide by polycondensation reaction in IL

ILs used as absorbents of CO2

The second important application of ILs is as CO2 absorbents. Currently, more
and more fossil fuels are burned on a global scale. As a result, CO2 emission
increases day by day, which is widely acknowledged as one of the causes of
5 
 

global warming. Physical absorption and chemical absorption are two main
methods used nowadays in industry to remove CO2 from large point sources
such as power plants. For physical absorption, polyethylene glycol and methanol
28

are the most commonly used gas absorbents.

For chemical absorption,

aqueous monoethanol amine (MEA) is the gas absorbent used.

29

Currently,

MEA process is used in more than 95 % of natural gas sweetening operations in
30

U.S.

Scheme 1.4. shows the carbamate mechanism for CO2 capture using

aqueous amine solutions. However, both physical and chemical absorption
methods currently used have serious drawbacks. Polyethylene glycol suffers
problems such as thermal degradation. On the other hand, methanol suffers from
its volatility. In the case of the MEA method, things get even worse. It suffers
from volatility of water and amines. Furthermore, amines are prone to thermal
degradation, and they are corrosive to steel.

Scheme 1.4. Carbamate mechanism for CO2 capture using aqueous amine
solutions

Due to their good solubility and selectivity to CO2, non-volatility and thermal
stability,

ILs

have

been

studied

as
6 

 

a

promising

candidate

in

CO2

absorption.

8,31,32

Using ILs as absorbents at least overcome two major

problems encountered in the three methods mentioned above. ILs absorb CO2 in
two way, by physical absorption and chemical absorption respectively.
For physical absorption, the uptake mode is by intercalation of CO2 into the
natural cavities of ILs, which is confirmed by the fact that there would be a
volume expansion after CO2 absorption. The ability of ILs to physically absorb
CO2 was mainly affected by counter anions. A higher fluorination degree in
counter anions results in a higher CO2 absorption ratio, due to the interactions
33-36

between Lewis basic fluorine atom and Lewis acidic CO2.

Compared to the

widely used MEA process, the desorption of CO2 in ILs is much easier and
thermodynamically favored because absorption and desorption of CO2 in ILs are
based on weak physical interactions.

37

However, some drawbacks for physical

absorption of CO2 in ILs do exist. The first is that physical absorption in ILs must
be conducted under high pressure to ensure a satisfactory absorption while in
most cases this requirement cannot be met. The second is that physical
absorption is a slow process in ILs due to their high viscosities. Another
disadvantage is that the presence of water would decrease the ability of CO2
absorption in ILs, especially for hydrophilic ones.

7 
 

8

Another way for CO2 absorption in ILs is chemical absorption. ILs can trap CO2
via a carbene mechanism when the 1,3-dialkylimidazolium cations are paired
38

with a basic enough anion such as acetate.

Scheme 1.5 shows the reaction

between CO2 and 1-ethyl-3-methyl-imidazolium acetate. However, the CO2
uptake stoichiometry is quite low in this case.

Scheme 1.5. Reaction between CO2 and 1-ethyl-3-methyl-imidazolium acetate
via a carbene mechanism

To improve CO2 uptake stoichiometry, amine functional groups were introduced
into ILs, either in imidazolium cation

39,40

or its counter anion.

29,41

A maximum

stoichimetry of 0.5 was observed when amine group was introduced into
imidazolium cation.

39

On the other hand, the maximum stoichiometry could be as

high as 1 when the amine group was introduced into the counter anions.
8 
 

29

Scheme 1.6 shows two examples of the reaction schematics between CO2 and
IL with amine group in its counter anion.

Scheme 1.6. Two examples of reaction schematics between CO2 and IL with
amine group in its counter anion
 

ILs as electrolyte
With no doubts, one of the most important applications of ILs is as electrolytes in
electrochemical devices. Due to their non-volatility, non-flammability, wide
electrochemical window, high inherent conductivity, good solubility to a wide
range of materials including organic, inorganic and polymeric materials, and wide
thermal operating range, ILs have been used in electrochemical devices such as
lithium batteries, dye sensitized solar cells (DSSCs), fuel cells, supercapacitors
7

and so on.

ILs in lithium batteries
Due to their high energy density and energy efficiency, lithium battery has been
used in various electronic devices such as cellular phones, digital cameras,

9 
 

laptops and even in vehicles and other large-scale power systems.

42

However,

the current lithium battery system has an inherent safety problem due to its use
43

of volatile and flammable organic solvents as electrolyte solvents.   A typical
example of electrolyte in commercialized lithium battery is composed of ethylene
carbonate as the solvent and LiPF6 as the solute, with the addition of a linear
carbonate such as dimethyl carbonate as a co-solvent to increase the fluidity and
reduce melting points of the electrolyte. Under certain circumstances, the
electrolyte in lithium battery can ignite or even explode.

44

Therefore, it is highly

demanding to develop new and safe electrolytes as replacement of organic
solvent based electrolytes.
In recent years, ILs have received considerable interests as electrolyte materials
43,45-50

for lithium battery.

Compared to conventional organic solvent electrolytes,

IL electrolytes have several unique properties making them promising candidates
for lithium battery, such as non-volatility, non-flammability, wide electrochemical
window, high inherent conductivity and wide thermal operating range.

42

The non-

volatility not only allows the IL electrolyte based lithium battery to be operated in
sealed cells at elevated temperatures without venting, but also eliminates the
possibility of vapor ignition, thereby increasing the overall safety of the cell. ILs
have a wide electrochemical window of 4 ~ 5 eV, making them extremely
resistant to electrochemical oxidation and reduction. In addition, ILs possess high
ionic conductivities, usually around 10 mS/cm, which is equivalent to the best
10 
 

current organic solvent based electrolytes. Besides, IL based electrolytes have a
wide thermal operating range. Current organic solvent based lithium batteries
suffer from a limited operating temperature range, since the electrolytes used in
most commercial lithium batteries will deteriorate at temperatures higher than
60 °C. In addition, the irreversible reaction between dissolved lithium salts and
organic solvents, negatively affect the cell performance. Performance also
suffers when the temperature approaches - 20 °C, as most organic solvents used
in lithium batteries have a freezing point around this temperature. The
temperature limit problems can be easily addressed by IL electrolytes, as most
ILs are thermally stable to temperatures greater than 200 °C, and proper
selection of IL can yield solvents with freezing points as low as - 90 °C, resulting
in a much broader potential range of operating temperatures than current
electrolytes.
Here shows a recent example of ILs as electrolytes in lithium battery.
work,

a

poly(vinylidene

difluoride-co-hexafluoropropylene)

45

In this

(PVDF-HFP)

membrane was prepared and served as the host matrix for the preparation of ILbased polymer electrolytes by activation with N-butyl-N-methylpyrrolidinium
bis(trifluoromethanesulfonyl)imide (Py14TFSI) complexed with 1 M LiTFSI. The
IL-based polymer electrolyte showed high thermal and electrochemical stability,
high ionic conductivity (1.1 x 10

-4

S/cm at 0 °C), good compatibility with LiFePO4

electrode, good charge-discharge performance and delivering specific capacities
of 143 mA·h/g at 0.1 C-rates. Also, the IL-based polymer electrolyte exhibited
11 
 

stable cycle properties and therefore was demonstrated to be suitable for lithium
battery applications.
ILs in fuel cells
Fuel cell is a device that converts chemical energy into electrical energy via a
redox reaction. Fuel cells are different from batteries in that they require a
constant input of fuels to run, but they can produce electricity continuously as
long as fuels are supplied. In fuel cell, hydrogen is the most important fuel, but
alcohols such as methanol and hydrocarbons such as natural gas are also used.
Due to their high energy density, high conversion efficiency and low pollutant
emission,

51,52

fuel cell has been recognized as one of the most promising

energy sources which could provide clean and efficient energy for stationary and
mobile applications.

53

There are three kinds of fuel cells under active

development, including alkaline fuel cell (AFC), proton exchange membrane fuel
cell (PEMFC) and phosphoric acid fuel cell (PAFC).

52

Among them, PEMFC are

considered one of the most promising technologies for stationary power
generation and transportation applications.
In PEMFC, a major drawback of the most commonly used humidified
perfluorosulfonic acid-based membranes, represented by Nafion

TM

, is that they

cannot be used at temperatures higher than 100 °C because of the evaporation
of water and the resulting conductivity loss. However, operation at higher
temperatures is critical for improving performance of PEMFCs because it could
12 
 

enhance the reaction kinetic at both electrodes, improve the carbon monoxide
tolerance of the platinum catalyst in the anode, and simplify heat and water
53

managements.

For operation of PEMFC at higher temperatures, an anhydrous

proton conductivity mechanism is required. To partially overcome this problem,
one method is to use protic ILs instead of water.
Protic ILs, composed of Brønsted acids and bases, which can form hydrogen
bonds and act as proton carriers, have been considered as effective protontransferring carriers for high temperature PEMFCs. Greenbaum and coworkers
have prepared a homogeneous, freestanding, and thermal stable gel-type PEM
based on protic IL, 1-methyl-3-propyl imidazolium dihydrogen phosphate, and
phosphoric acid doped polybenzylimidazole. The PEM obtained had conductivity
of

-3

up to 2.0 x 10

S/cm at 150 °C under anhydrous condition. While after

absorbing some water vapor, the conductivity rises even higher.

54

In a recent

paper, Watanabe and coworkers have also prepared a composite PEM based on
sulfonated

polyimide

and

a

protic

IL,

diethylmethylammonium

trifluoromethanesulfonate. The ionic conductivity of PEM obtained was higher
-2

than 10

S/cm at 140 °C under anhydrous condition.

55

In addition, to prevent

the leakage problem of protic ILs when doped in composite membrane, Yan and
coworkers incorporated mesoporous silica nanoparticles.

54

The results revealed

that incorporation of proper amounts mesoporous silica nanoparticles not only
prevented the release of protic IL components from composite membrane, but

13 
 

also increased the proton conductivity, which was due to the capillary force of the
mesoporous silica nanoparticles and the ion transport channel formed in the
hybrid membranes.
ILs in DSSCs
Nowadays, one of the greatest challenges for global society is to find ways to
replace the vanishing fossil fuel supplies with renewable resources such as wind
energy, nuclear energy and solar energy.

56

Among them, solar energy is

expected to play a key role, since the sun provides approximately 120,000
tetrawatts to the Earth, which is about 6,000 times more than the current world's
energy consumption rate. It has been estimated that our current energy needs
can be met by covering 0.1 % of the Earth's surface with photovoltaic
installations with a light-to-power conversion efficiency of 10 %. So far, siliconbased solid-state junction devices have dominated in the area of photovoltaic
solar energy converters and served a rapidly growing market, which was
57

expected to rise to 300 GW by 2030.

However, compared to the fossil or

nuclear energy, the cost of photovoltaic electricity production is still too high.
In recent years, DSSCs have been extensively studied as a low-cost alternative
to commercial silicon-based cells.

58-60

Photoexcitation of the sensitizer (S) is

followed by electron injection into the conduction band of a semiconductor oxide
film. The sensitizer is regenerated by the redox system, which itself is
regenerated at the counter electrode by electrons passed through the load.
14 
 

56

Here, ruthenium dye is the most commonly used sensitizer, with nanocrystalline
-

-

TiO2 as the semiconductor oxide film and I /I3 as the redox couple. Till now, the
highest light-to-power conversion efficiency of DSSCs achieved based on
61

organic solvent electrolyte exceeds 12 %.

However, hermetic sealing of volatile

electrolytes is costly and counteracts the merit of DSSCs as low-cost alternatives
to silicon-based photovoltaic devices. In addition, encapsulation of volatile
solvents is a critical issue for long-term device stability. Hence, it is very
important to investigate non-volatile electrolytes for the development of DSSCs.
ILs, due to their non-volatility, non-flammability, good thermal and chemical
stability, have been extensively studied as electrolyte materials for DSSCs in
62,63

recent years.

However, due to the intrinsic high viscosity and the resulting

low conductivity of ILs, DSSCs based on ILs electrolytes usually showed lower
conversion efficiency compared to volatile solvent based ones.

64-66

To reduce

the viscosities of IL based electrolytes, Grätzel and coworkers have fabricated
DSSCs based on mixtures of three different ILs (including1,3-dimethlymidazolium
iodide, 1-ethyl-3-methylimidazolium iodide, and 1-ethyl-3-methylimidazolium
tetracyanoborate) and achieved an efficiency of 8.2 %.

67

In addition, by further

structure optimization of the ruthenium dye, higher efficiency 9.1 % was
achieved.

68

Though ILs based DSSCs showed conversion efficiency lower than

volatile solvents based ones, the long-term stability was greatly improved. Kato
and coworkers compared the long-term performance of two different electrolytes,
15 
 

one based on volatile solvents γ-butyrolactone and the other based on IL, 1,2dimethyl-3-propylimidazolium iodide.

69,70

The results revealed that the DSSC

using IL electrolyte reduced the deterioration factor to one sixth of the one using
volatile solvents. The lifetime for outdoor use was estimated over 15 years for IL
electrolyte based DSSC, while for volatile solvents based ones, the lifetime was
only 2.5 years.
Poly(ionic liquids) (PILs)
Though ILs have been extensively studied and successfully applied in many
areas, the intrinsic liquid properties of ILs presented a fabrication issue in
industrial production. More recently, there has been growing interest in the
polymeric forms of ILs (PILs), which combined the unique properties of ILs and
polymer architecture. Compared to ILs, PILs have improved processability and
durability, better mechanical stability, and improved control of their meso- to
nano-structure.
Formation of PILs
There have been mainly three kinds of PILs reported in literature: PILs composed
of polycations and free anions, PILs composed of polyanions and free cations,
and zwitterionic PILs.

16 
 

PILs composed of polycations and free anions
Most PILs synthesized so far are PILs composed of cations in their polymer
backbone and free anions. Among them, imidazolium cations

71-79

were the most

common ones used. Other cations such as tetraalkyl ammonium,
pyridinium,

80,86,87

pyrrolidonium,

88-91

and guanidinium

92,93

80-85

have also been

synthesized. On the other hand, the most popular anions in PILs include chloride,
bromide,

iodide,

thiocyanate,

bis(trifluoromethanesulfonyl)imide.
vinyl,

71,72,80,86,87,94-97

styrenic,

tetrafluoroborate,
6

For

hexafluorophosphate

polymerizable

74,75,81,98

functional

and (meth)acrylic

and

groups,

80,82,83,85,88,93,99

are the most popular ones. Scheme 1.7 shows the most commonly seen
polycationic PILs in literature.

Scheme 1.7. Structures of the most common polycationic PILs

17 
 

PILs composed of polyanions and free cations
So far, the number of PILs composed of polyanions and free cations has been
much smaller compared to those polycationic ones. In 2004, Ohno and
coworkers published a paper describing the synthesis of a new class of PILs with
polyanion backbones. In this paper, a series of PILs based on vinyl carbonate,
vinyl

sulphonate,

vinyl

phosphonate,

styrenyl

sulphonate,

methacryloyl
100

sulphonate anions and free imidazolium cations were synthesized.

The

structure of PILs synthesized are shown in Scheme 1.8.

Scheme 1.8. Structures of PILs with polyanions and free cations.

On

the

other

hand,

PILs

trifluoromethanesulfonamide

with
and

more
cations

sophisticated
other

than

tetraalkylammonium cations have also been synthesized.
are shown in Scheme 1.9.

18 
 

anions

such

imidazolium

101,102

as
like

The structures

Scheme 1.9. Polyanionic PILs with trifluoromethanesulfonamide anion (left) and
cations other than imidazolium like tetraalkylammonium cations (right)

Zwitterionic PILs
Another type of PILs called zwitterionic PILs has also been synthesized, in which
both cations and anions are covalently linked in the polymer backbone. The
conductivities of zwitterionic PILs are quite low, which are around 10

-9

S/cm. This

is because the cations and anions in PILs cannot move under external voltage.
However, when salts like LiTFSI were added, the dissociated ions from added
salts could behave as charge carriers and the conductivity of the PILs
electrolytes could be elevated, usually several orders of magnitude higher.
Several examples of reported zwitterionic PILs were listed in Scheme 1.10.
105

19 
 

103-

Scheme 1.10. Zwitterionic PILs reported in literature

Synthesis of PILs
PILs can be synthesized in two methods: (1) direct polymerization of IL
monomers, (2) chemical modification of existing polymers. In each method,
several

polymerization

conventional

94,105-108

polymerization,

113

techniques

have

been

employed,

and controlled radical polymerization,
114

ring-opening polymerization

109-112

and others.

including
step-growth

115,116

Direct polymerization of IL monomers
An IL monomer is an IL containing one or more polymerizable units, such as vinyl,
(meth)acryloyl and stryrenic groups. The polymerization of IL monomers is a
straightforward and widely adopted strategy to form PILs, which results in a
homogeneous polyelectrolyte possessing the same type of IL moiety in each
repeating unit. Scheme 1.11 shows a general approach for the preparation and
6

polymerization of methacryloyl based IL monomers . Methacryloyl chloride first
reacted with an hydroxyl-containing haloalkane to form an ester. Then, the
20 
 

haloalkane bearing ester obtained was further quarternized by an N-alkyl
imidazole to form an IL monomer. In the third step, the IL monomer was
polymerized in the presence of a initiator, such as 2,2'-azo-bis-isobutyronitrile
(AIBN).

Scheme 1.11. General synthetic route to PILs from methacryloyl IL monomers
bearing imidazolium species. (R: alkyl chain; X: halide)

Chemical modification of existing polymers
PILs can also be prepared by chemical modification of existing polymers. This
strategy ensures the PILs formed have the same architecture, monomer
composition and degree of polymerization present in the original polymers.
Besides, by chemical modification of the carefully chosen precursor polymers,
this strategy enables preparation of some PILs with unique structures and
compositions, which are inaccessible by direct polymerization of IL monomers. In
2005, Shen and coworkers reported the preparation of a PIL by chemical
modification.
polymerized

109

As shown in Scheme 1.12, 4-chloromethylstryrene was first

via

RAFT

polymerization
21 

 

and

then

quarternized

with

N-

butylimidazole to form a PIL, poly(1-butyl-3-vinylbenzylimidazolium chloride). The
quarternization reaction was quantitative, as confirmed by vanishing signals of
chloromethyl group in

1

H NMR spectrum. Block copolymers containing PIL

segment could also be prepared by post-polymerization modification.
shown

in

Scheme

chloromethylstyrene)

1.13,
was

a
first

diblock

copolymer

synthesized

via

117

As

polystryrene-b-poly(4a

nitroxide-mediated

polymerization. Since the polystyrene segment would not react with Nmethylimidazole, only the poly(4-chloromethylstyrene) segment was converted to
poly(1-methyl-3-vinylbenzylimidazolium chloride). Again, a nearly quantitative
conversion (> 99%) was observed for poly(4-chloromethylstyrene) segment, as
1

confirmed by H NMR and microanalysis.

Scheme 1.12. Synthesis of poly(1-butyl-3-vinylbenzylimidazolium chloride) by
post-polymerization modification of poly(p-chloromethylstyrene).

22 
 

Scheme 1.13. Synthetic route to PS-b-PMVBI block copolymers via postpolymerization modification of a preformed diblock copolymer

Application of PILs
With no doubts, one of the major driving forces for preparing and studying PILs is
to harness their potential as novel polymer electrolyte in electrochemical devices
such as lithium battery,

91,118

DSSC

119,120

and fuel cell.

92

Compared to IL

electrolyte, solid state polymer electrolyte has important advantages such as
mechanical stability, safety and easy processing. In addition, polymeric
electrolyte may potentially permit production of flexible and transparent ion
23 
 

conductive materials with defined size and shape, such as thin films, fibers and
coatings. However, compared to ILs, PILs generally have lower conductivity,
usually several orders of magnitude, which is due to both reduced number of
mobile ions after covalent bonding of the polymerizable ions and the increased
glass transition temperature.

94,106

Factors affecting ionic conductivity of PILs
There are a lot of factors affecting the ionic conductivity of PILs, such as the
counter anion, the structure and length of spacer between backbone and
imidazolium cation, the alkyl chain on the imidazolium ring, the structures of the
cations, the immobilization of anions on the backbone, degree of polymerization,
crosslinking and presence of copolymers.
Anion effect on ionic conductivity of PILs
Ohno and coworkers have systematically studied the structure-related ionic
conductivity of (meth)acryloyl- and N-vinylimidazolium-based PILs. In 1999,
Yoshizawa and Ohno first reported an methacryloyl-based PIL prepared for this
purpose.

106

In this article, a poly(ethylene oxide) (PEO) derivative with both

methacryloyl group and imidazolium salt structure on its ends were prepared and
polymerized. The structure of the macromonomer was shown in Scheme 1.14.
The macromonomer was polymerized in bulk via free radical polymerization
using AIBN as the initiator to form PIL. The obtained PIL was a rubber-like
material with high ionic conductivity and low Tg, though the degree of
24 
 

polymerization was not clear. The effect of different anions on PIL conductivity
was examined. As shown in Table 1.1 and Figure 1.1, PIL (X = Cl or TFSI)
showed quite close Tg, while the conductivity differed a lot, around 3 orders of
magnitude. This was attributed to the molten salts formation and much weaker
interaction force of ether oxygens towards TFSI or Cl. Since TFSI has a much
larger ion radius (325 pm) compared to Cl (181 pm) and the surface charge
density should be much smaller in TFSI. PIL with TFSI as counter anion showed
an excellent conductivity of 1.20 x 10

-4

S/cm at 30 °C.

Scheme1.14. Structure of macromonomer (X = Cl or TFSI).

Table 1.1. Tg of macromonomers and PILs
Tg / °C
-74
-72
-62
-64

Macromonomer X = Cl
Macromonomer X = TFSI
PIL X = Cl
PIL X = TFSI

25 
 

Figure 1.1. Temperature dependence of the ionic conductivity of
macromonomers (●,X = TFSI;▲, X = Cl) and their corresponding polymers (○,
X = TFSI, △, X = Cl). (Reprinted with permission from Chem Lett 1999, 889-890.
Copyright 1999 The Chemical Society of Japan)

Effect of spacer structure and length on ionic conductivity of PILs
The effect of different spacer structure and spacer length on conductivity of PIL
100,121

was also systematically studied.
macromonomers

based

on

For this purpose, two sets of

(meth)acryloyl

polymerizable

groups

were

synthesized. The structures of macromonomers are shown in Scheme 1.15. The
26 
 

PILs were prepared by free radical polymerization of these macromomomers and
no degree of polymerization was reported. As shown in Figure 1.2, the ionic
conductivity increased with increasing spacer length, which was attributed to the
fact that imidazolim cation turned more mobile with longer flexible spacer. In
addition, the ionic conductivity of PILs with alkyl chain spacer was higher than
that of PEO spacer in all chain length. This improvement was mainly due to much
weaker interaction force of alkyl chains toward TFSI anions compared to PEO
-4

ones. The highest conductivity achieved was 3.62 x 10
ethylene repeating units as spacer.

27 
 

S/cm from PIL7 with six

Scheme 1.15. Structures of macromonomers based on (meth)acryloyl groups

28 
 

Figure 1.2. Effect of spacer structure and length on the ionic conductivity for PILs.
(Reprinted with permission from Electrochim Acta 2001, 46, 1723-1728.
Copyright 2001 Elsevier Science Ltd)

Effect of alkyl chains on imidazoium ring on ionic conductivity of PILs
The effect of alkyl chain on imidazolium ring was also studied. Three
methacrylate based macromonomers 1, 3, and 4 with different alkyl chains were
prepared and polymerized. (Structures shown in Scheme 1.15) As shown in
Figure 1.3, PILs with ethyl group on imidazolium ring had the highest
conductivities. However, the effect of alkyl chains on imidazolium ring was not as
significant as spacer length and counter anions on the conductivity of PILs.

29 
 

Figure 1.3. Effect of alkyl chain on the ionic conductivity and Tg for
macromonomer 1, 3, 4 and their corresponding PILs. (Reprinted with permission
from Electrochim Acta 2001, 46, 1723-1728. Copyright 2001 Elsevier Science Ltd)

Effect of cation structures on ionic conductivity of PILs
Cation structures other than imidazolium were prepared and their effects on ionic
88

conductivity were also studied.

A series of acryloyl-bearing monomers with

different cation structures including imidazolium, pyrrolinium, pyrrolidinium and
piperidinium were polymerized via free radical polymerization. The structures
were shown in Scheme 1.16. The conductivities of the corresponding PILs were
shown in Figure 1.4. As shown in Figure 1.4, PILs with imidazolium cations
showed higher conductivities compared to PILs with other cation structures,
30 
 

except in the case of 1-ethyl-2-methylimidazolium. And again, as mentioned
above, PILs with ethylimidazolium cation showed the highest conductivity. These
studies revealed that modification of the cation structures was not as significant
as spacer length (i.e., chain flexibility) and anion size in determining the
conductivities of the PILs.

Scheme 1.16. Monomers with different cation structures

31 
 

Figure 1.4. Conductivities of PILs with different cation structures (Reprinted with
permission from Electrochim Acta 2006, 51, 2614-2619. Copyright 2006 Elsevier
Science Ltd)

Effect of immobilizing anions on the backbone with free cations on ionic
conductivity of PILs
Another attempt to improve the polymer ionic conductivity was to prepare
100

polyanion type of PILs.

Polymerization through the anion was considered to

be effective in maintaining the flexibility of imidazolium cation, potentially
resulting in higher ionic conductivity of the PILs. To investigate the effect of anion
structure on the ionic conductivity, four different monomers were prepared by
neutralizing N-ethylimidazole with acrylic acid, vinylsulfonic acid, vinylphosphonic
32 
 

acid and p- styrenesulfonic acid, as shown in Scheme 1.17. All four monomers
were polymerized via free radical polymerization and PILs based on vinylsulfonic
acid exhibited the lowest Tg and thus the highest ionic conductivity (1.1 x 10

-4

S/cm) at room temperature, which was in the same range compared to
polycation type PILs with long flexible spacers.

106

Scheme 1.17. Structures of IL monomers with immobilizing anions and free
imidazolium cations

The effect of alkyl spacer on the ionic conductivity of polyanion type PILs was
also studied. Scheme 1.18 shows the synthesis of IL monomer with alkyl spacer
between methacrylate and sulfonate group. After polymerization, the conductivity
33 
 

was measured and compared to that of PIL based on vinylsulfonic acid, as
shown in Figure 1.5. Both PILs showed ionic conductivity around 10

-4

S/cm at

room temperature, which was explained by the fact that the flexibility of
imidazolium cation in polyanion type PILs was inherently high and the
conductivity would not be improved by the introduction of alkyl spacers.

Scheme 1.18. Synthesis of IL monomer with alkyl spacer between vinyl group
and sulfonate

34 
 

Figure 1.5. Temperature dependence of the ionic conductivity for EImVS,
EImC3S, and their polymers. (○) EImVS, (●) P(EImVS), (△) EImC3S, (▲)
P(EImC3S). P implies polymerized system. (Reprinted with permission from
Electrochim Acta 2004, 50, 255-261. Copyright 2004 Elsevier Science Ltd)

Effect of degree of polymerization on ionic conductivity of PILs
The effect of degree of polymerization on ionic conductivity of PIL was also
examined.

100,108

PIL based on a vinyl imidazolium cation with a vinyl sulfonate

anion was prepared by free radical polymerization, Scheme 1.19. After 3 h, the
resultant copolymer showed a poor conductivity of 8.5 x 10
35 
 

-5

S/cm at 30 °C.

However, increased polymerization time decreased the ionic conductivity. After 6
h, the resultant copolymer showed a much poorer conductivity of lower than 10

-9

S/cm, suggesting that increased molecular weight lowered ionic conductivity.

Scheme 1.19. Monomer with vinyl imidazolium cation and vinyl sulfonate anion

Effect of crosslinking on ionic conductivity of PILs
As mentioned above, PIL with a long alkyl spacer would have high ionic
conductivity. PIL based on acrylate with six repeating methylene units as spacer
showed an ionic conductivity of 1.37 x 10

-4

S/cm at 30 °C, Scheme 1.20.

122

However, it was difficult to handle due to its sticky characteristics. One way to
solve this problem was to make flexible films by the addition of cross-linkers. The
structures of cross-linkers used were shown in Scheme 1.21. After addition of a
small amount of cross-linkers, PIL formed flexible films and it was confirmed that
adding only 1 mol% cross-linker was enough to obtain flexible films. With
increasing amount of the cross-linker, the film formation changed gradually into a
self standing film.

36 
 

Scheme 1.20. Structure of acrylate based PIL with six repeating methylene units
as the spacer

Scheme 1.21. Structures of cross-linkers used

37 
 

Figure 1.6. The photograph of film electrolyte composed of PIL and 3 mol% E3V
cross-linker (Reprinted with permission from Polymer 2004, 45, 1577-1582.
Copyright 2004 Elsevier Science Ltd)

Figure 1.6 shows the picture of a flexible self-standing film prepared with 3 mol%
of cross-linker E3V. The effect of cross-linker on ionic conductivity of PIL films
was examined. As shown in Figure 1.7, with the addition of 0.5 mol% E3V, the Tg
of PIL film increased about 5 °C compared to that of the linear polymer, and thus
ionic conductivity dropped to nearly half of that of the linear polymer. In addition,
with more E3V added, the Tg and ionic conductivity did not change much. The Tg
increase could be explained as cross-linking restricted the motion of polymer
backbone thus resulting in a decrease of ionic conductivity. The effect of spacer
length and polymerizable group of the cross-linkers on the ionic conductivity of
PIL films were also examined. Different cross-linkers, as shown in Scheme 1.22,
38 
 

were added to PILs, while keeping the concentration constant as 1.3 mol%. The
conductivity data was shown in Figure 1.8. For cross-linker ExV, PIL film with
E3V showed higher conductivity. For cross-linker EyA, E4A performed the best
and the film showed almost same conductivity compared to linear PIL. While in
the case of EzM, E9M exhibited slightly higher conductivity than the other two. It
was concluded that introducing cross-linker had a negative effect on the ionic
conductivity of PILs. However, with selection of an appropriate spacer, this
negative effect could be alleviated.

39 
 

Figure 1.7. The effect of cross-linker (E3V) concentration on the ionic
conductivity and Tg of the PIL film (Reprinted with permission from Polymer 2004,
45, 1577-1582. Copyright 2004 Elsevier Science Ltd)

40 
 

Figure 1.8. Temperature dependence of the ionic conductivity for PIL films with
different cross-linkers (X = 2 or 3) (Reprinted with permission from Polymer 2004,
45, 1577-1582. Copyright 2004 Elsevier Science Ltd)

41 
 

Figure 1.9. Temperature dependence of the ionic conductivity for PIL films with
different cross-linkers (y = 4 or 13-14) (Reprinted with permission from Polymer
2004, 45, 1577-1582. Copyright 2004 Elsevier Science Ltd)

42 
 

Figure 1.10. Temperature dependence of the ionic conductivity for PIL films with
different cross-linkers (z = 2 or 9) (Reprinted with permission from Polymer 2004,
45, 1577-1582. Copyright 2004 Elsevier Science Ltd)

Effect of copolymer on the conductivity of PILs
Introducing an additional component to PIL backbone was another way to
increase ionic conductivity. Elabd and coworkers studied the effect of random
copolymer composition on ionic conductivity of PILs.

123

Two different sets of

random copolymer were synthesized which they named as nonionic-ionic
copolymer and ionic-ionic copolymer respectively. Nonionic-ionic copolymer was
prepared by free radical polymerization of a nonionic monomer n-hexyl
43 
 

methacrylate

(HMA)

and

an

ionic

monomer

1-(2-methacryloyl)ethyl)-3-

butylimidazolium tetrafluoroborate (MEBIm-BF4). Ionic-ionic copolymer was
-

prepared by replacing a proportion of the BF4 anions in the homopolymer of
poly(1-(2-methacryloyl)ethyl)-3-butylimidazolium tetrafluoroborate) with TFSI.
Scheme 1.22 shows the structures of two kinds of random copolymers. A series
of nonionic-ionic copolymers with different composition of HMA were obtained by
tuning the HMA concentration in the free radical polymerization. The effect of
introducing HMA on Tg and ionic conductivity was studied, as shown in Figure
1.9. The conductivity increased with increasing amount of HMA. This was
explained as that the reduction in Tg with increasing HMA composition had a
more significant effect on ionic conductivity compared to the reduction in charge
carriers concentration, which one would expect a decrease in ionic conductivity.
On the other hand, ionic conductivity of copolymer started to decrease at 67.5
mol% HMA composition. This was probably due to that the effect of low
concentration of charge carriers overwhelmed that of Tg decrease.

44 
 

Scheme 1.22. Structures of Nonionic-Ionic random copolymer and Ionic-Ionic
random copolymer

45 
 

Figure 1.11. Temperature dependence of ionic conductivity for poly(HMA-coMEBIm-BF4)  (Reprinted with permission from Macromolecules 2009, 42, 48094816. Copyright 2009 American Chemical Society)

46 
 

Figure 1.12. Composition and glass transition dependence of ionic conductivity
for poly(HMA-co-MEBIm-BF4)  (Reprinted with permission from Macromolecules
2009, 42, 4809-4816. Copyright 2009 American Chemical Society)

The effect of anion exchange on ionic conductivity of copolymers was also
studied with the results shown in Figure 1.10. As expected, with the increase of
TFSI composition in the copolymer, the ionic conductivity increased. This was
mainly attributed to the reduction in Tg after introducing TFSI, because the
negative charge on TFSI was more delocalized than BF4 resulting in much
weaker interactions between the counter anions and imidazolium cations.

47 
 

Besides, unlike the HMA copolymers, the increase in ionic conductivity was
continuous over the composition range investigated.

Figure 1.13. Temperature dependence of ionic conductivity for poly(MEBImTFSI-co-MEBIm-BF4)  (Reprinted with permission from Macromolecules 2009, 42,
4809-4816. Copyright 2009 American Chemical Society)

48 
 

Figure 1.14. Composition and glass transition dependence of ionic conductivity
permission from
for poly(MEBIm-TFSI-co-MEBIm-BF4)  (Reprinted with
Macromolecules 2009, 42, 4809-4816. Copyright 2009 American Chemical
Society)

49 
 

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Mecerreyes, D.; Taton, D.; Gnanou, Y.: Synthesis by RAFT and ionic
responsiveness of double hydrophilic block copolymers based on ionic liquid
monomer units. Macromolecules 2008, 41, 6299-6308.
(111) Yang, J.; Sun, W. L.; Lin, W. H.; Shen, Z. Q.: Synthesis and magnetic
properties of comb-like copolymeric complexes based on thiazole ring and ionic
liquid. J Polym Sci Pol Chem 2008, 46, 5123-5132.
(112) Yuan, J. Y.; Schlaad, H.; Giordano, C.; Antonietti, M.: Double hydrophilic
diblock copolymers containing a poly(ionic liquid) segment: Controlled synthesis,
solution property, and application as carbon precursor. Eur Polym J 2011, 47,
772-781.
(113) Stathatos, E.; Jovanovski, V.; Orel, B.; Jerman, I.; Lianos, P.: Dyesensitized solar cells made by using a polysilsesquioxane polymeric ionic fluid as
redox electrolyte. J Phys Chem C 2007, 111, 6528-6532.
(114) Vygodskii, Y. S.; Shaplov, A. S.; Lozinskaya, E. I.; Lyssenko, K. A.;
Golovanov, D. G.; Malyshkina, I. A.; Gavrilova, N. D.; Buchmeiser, M. R.:
Conductive polymer electrolytes derived from poly(norbornene)s with pendant
ionic imidazolium moieties. Macromol Chem Physic 2008, 209, 40-51.
(115) Burns, C. T.; Lee, S.; Seifert, S.; Firestone, M. A.: Thiophene-based ionic
liquids: synthesis, physical properties, self-assembly, and oxidative
polymerization. Polym Adv Technol 2008, 19, 1369-1382.
(116) Lee, S.; Becht, G. A.; Lee, B.; Burns, C. T.; Firestone, M. A.:
Electropolymerization of a bifunctional ionic liquid monomer yields an
electroactive liquid-crystalline polymer. Adv Funct Mater 2010, 20, 2063-2070.
(117) Stancik, C. M.; Lavoie, A. R.; Achurra, P. A.; Waymouth, R. M.; Gast, A. P.:
A neutron scattering study of the structure and water partitioning of selectively
deuterated copolymer micelles. Langmuir 2004, 20, 8975-8987.
(118) Li, M. T.; Dong, S. M.; Fang, S. H.; Yang, L.; Hirano, S. I.; Hu, J. Y.;
Huang, X. M.: Polymeric ionic liquid membranes as electrolytes for lithium battery
applications. J Appl Electrochem 2012, 42, 851-856.

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(119) Suzuki, K.; Yamaguchi, M.; Hotta, S.; Tanabe, N.; Yanagida, S.: A new
alkyl-imidazole polymer prepared as an inonic polymer electrolyte by in situ
polymerization of dye sensitized solar cells. J Photoch Photobio A 2004, 164, 8185.
(120) Wu, J. H.; Hao, S.; Lan, Z.; Lin, J. M.; Huang, M. L.; Huang, Y. F.; Li, P. J.;
Yin, S.; Satot, T.: An all-solid-state dye-sensitized solar cell-based poly(N-alkyl-4vinyl-pyridine iodide) electrolyte with efficiency of 5.64%. J Am Chem Soc 2008,
130, 11568-11569.
(121) Yoshizawa, M.; Ohno, H.: Synthesis of molten salt-type polymer brush and
effect of brush structure on the ionic conductivity. Electrochim Acta 2001, 46,
1723-1728.
(122) Washiro, S.; Yoshizawa, M.; Nakajima, H.; Ohno, H.: Highly ion
conductive flexible films composed of network polymers based on polymerizable
ionic liquids. Polymer 2004, 45, 1577-1582.
(123) Chen, H.; Choi, J. H.; Salas-de La Cruz, D.; Winey, K. I.; Elabd, Y. A.:
Polymerized ionic liquids: The effect of random copolymer composition on ion
conduction. Macromolecules 2009, 42, 4809-4816. 
 
 

63 
 

Chapter 2 Synthesis and characterization of novel low Tg poly(ionic liquids)

Introduction
In the past few years, poly(ionic liquids) (PILs), which combined the unique
properties of ionic liquids and polymer architecture, have attracted a lot of
attention.

1-8

Compared to ILs, PILs have enhanced mechanical stability,

improved processability and durability. In addition to utilities as polymer
electrolytes in electrochemical devices,
gas absorption and separation,
18,19

block copolymers.

12-15

1-5,9-11

PILs also found applications in

porous polymers

16,17

and components in

However, one critical drawback for PILs is that once

polymerized, the conductivity usually suffers a huge decrease compared to their
1

monomers.

To obtain high ionic conductivity PILs, people have tried many different methods,
such

as

replacing

halide

anion

with
- 1-4

bis(trifluoromethanesulfonyl)imide (N(SO2CF3)2 ),

larger

anions

like

introducing long alkyl chain

or oligo-ethylene oxide chain between the vinyl group and the imidazolium ion,
and polymerizing the IL anion to retain the mobility of imidazolium cation.

2-4

20-22

Among these methods, introducing long alkyl or oligo-ethylene oxide chain
turned out to be very effective due to their flexible nature, which could greatly
enhance the mobility of imidazolium cations. For example, an ionic monomer 1-

64 
 

ethyl-3-vinylimidazolium

bis(trifluoromethanesulfonyl)imide
-2

conductivity around 2 x 10
dropped to around 10
magnitude.

1

-7

had

an

ionic

S/cm at 30 oC. Once polymerized, the conductivity

S/cm at 30 oC, a decrease of more than 5 orders of

However, the huge ionic conductivity decrease could be greatly

alleviated by introducing a poly(ethylene oxide) (PEO) oligomer spacer. For
example,

a

macromonomer

1-ethyl-3-(poly(ethylene

oxide)

mono-

methacrylate)imidazolium bis(trifluoromethanesulfonyl)imide (molecular weight of
PEO part is about 350 g/mol) had an ionic conductivity of around 2 x 10

-3

S/cm

at 30 oC. After polymerization, the polymer showed a conductivity of 1.2 x 10

-4

2

S/cm at 30 oC, only 1 order of magnitude decrease. In a recent study, Döbbelin
and co-workers synthesized a pyrrolidinium-based PIL with poly(ethylene glycol)
(PEG) side chains on the pyrrolidinium ring to improve its ionic conductivity.

23

The results confirmed that ILs or IL/PIL mixture with a pendant PEG chain
exhibited a higher conductivity compared to those with a butyl group. However,
due to the solid nature of PILs synthesized, there was no conductivity data about
those pure PILs.
In this chapter, a series of novel PILs based on flexible polyepichlorohydrin
backbone were synthesized and the effect of increasing chain length was studied.
The first step was to synthesize high molecular weight polyEPCH using a
literature method.

24

The ring-opening polymerization of epichlorohydrin has been

65 
 

studied for many years. Generally speaking, there are two main methods for ringopening

polymerization,

that

is,

anionic

25,26

and

27-29

cationic.

For

epichlorohydrin, anionic ring-opening polymerization is generally prohibited due
to the predominant reaction between the chloromethyl group of epichlorohydrin
and strong nucleophilic bases used as initiator in conventional anionic
polymerization. Therefore, the strategies developed up to now are mainly based
on cationic or coordinated ring-opening polymerizations.

24

For cationic ring-opening polymerization of epichlorohydrin, there are two
different mechanisms: one is called activated chain end mechanisms (ACE) and
28

the other called monomer activated mechanism (AM),

shown in Scheme 2.1. In

the ACE mechanism, the active propagating center is an oxonium cation located
in the chain end while the monomer is neutral. The initiating system for ACE
mechanism usually contained a Lewis acid in combination with a small portion of
protogenic species (often water). Due to the side reactions including chain
transfer, backbiting and termination between propagating species and the
oxygen atoms in the polymer chain, the product in ACE mechanism was usually
a mixture of ill-defined linear or cyclic polyEPCH oligomers. On the other side, in
AM mechanism, the chain end was a neutral hydroxyl, while the monomer
formed an ionic complex with a protonic species (a Brönsted acid). The ringopening polymerization took place at low instantaneous EPCH concentration. In
the presence of initiator system containing a Lewis acid (usually BF3) and a low
mass diol (PEG oligomer or 1,4-butanediol), the formation of cyclic oligomer was
66 
 

strongly suppressed (lower than 0.7 wt%), and the main product was
dihydroxytelechelic polyEPCH. However, even in AM mechanism, the molecular
weight of polyEPCH obtained was lower than 2,500 g/mol.

27

Scheme 2.1. ACE and AM mechanism for cationic ring-opening polymerization
of epichlorohydrin

One of the ways to improve on the anionic polymerization is to use a novel
weakly nucleophilic initiating system, including triisobutylaluminum (i-Bu3Al) and
tetraoctylammonium bromide (NOct4Br). i-Bu3Al formed not only a low
nucleophilicity 1 : 1 complex with NOct4Br, but also a strongly activating complex
with EPCH monomer (Scheme 2.2). For this reason, the amount of i-Bu3Al
added should be slightly more than NOct4Br. Under this condition, the reactivity
67 
 

of EPCH toward nucleophiles was greatly enhanced and the polymerization
could proceed well without using strong nucleophiles as in conventional anionic
ring-opening polymerizations. More importantly, the chloromethyl group in EPCH
was preserved and could be used for further chemical modification.

Scheme 2.2. Mechanism for NOct4Br, i-Bu3Al initiated anionic polymerization of
epichlorohydrin

3

In this chapter, a series of polyEPCH with molecular weight from 21.6 x 10 to
3

76.2 x 10 g/mol were synthesized. The polyEPCH obtained was treated with 168 
 

-

butylimidazole to form a PIL with Cl , which was followed by an ion exchange
-

-

reaction in water to replace Cl with TFSI . All PILs obtained revealed good
thermal stabilities, high ionic conductivities and high viscosities, making them
promising electrolyte candidates for a wide range of electrochemical device
applications.

Results and discussion
Synthesis of polyepichlorohydrin based poly(ionic liquids)
The synthesis of polyEPCH was carried out by anionic polymerization using a
literature method.

24

As shown in Scheme 2.3, tetraoctylammonium bromide

(NOct4Br) was used as initiator and triisobutylaluminum (i-Bu3Al, 1M in toluene)
as catalyst. The polymerization was carried out in a toluene solution from -30 oC
to room temperature. PolyEPCH with different molecular weight was obtained by
tuning the monomer to initiator molar ratio from 100 to 500. The key point to
ensure successful polymerization was the amount of i-Bu3Al added. As shown in
Table 2.1, no polymerization took place at a ratio [M]/[Al]/[NOct4Br] equal to
100/1/1, whereas 100 % conversion was achieved at the ratio 100/1.5/1. With the
increase of [M]/[NOct4Br] ratio, more i-Bu3Al should be added, because more i-

69 
 

Bu3Al was needed to activate the EPCH monomer. With the addition of
appropriate amount of i-Bu3Al, the conversion for all three polymerization of
EPCH was 100 %, and a yield around 88 % was achieved. PolyGBIMCl was
synthesized by quaternarization of polyEPCH with 1-butylimidazole. In this case,
1-butylimidazole was used both as the reactant and the solvent. The solution was
degassed with the freeze-pump-thaw procedure three times, inserted into oil bath
at 115 oC and refluxed under N2 overnight. In this step, degassing and refluxing
under N2 proctection was very important because if not, side reactions such as
oxidation would happen and the product would turn black. In the end, the product
was dissolved in chloroform and precipitated from ethyl ether. Unreacted
polyEPCH and 1-butylimidazole dissolved in ethyl ether while polyGBIMCl did not.
The product was dried by heating at 100 oC in vacuo. PolyGBIMCl was a highly
hygroscopic solid at room temperature. PolyGBIMTFSI was then obtained by an
ion exchange reaction. After dissolving PolyGBIMCl in aqueous solution, LiTFSI
was added and the solution turned milky immediately. The product was
precipitated out after 30 min centrifugation and purified by washing with Milli-Q
water three times. The product was dried by heating at 100 oC in vacuo overnight.
PolyGBIMTFSI was a highly viscous liquid.

70 
 

Scheme 2.3. Synthesis of polyEPCH and polyGBIMTFSI

Table 2.1. Polymerization of epichlorohydrin initiated by NOct4Br/ i-Bu3Al
a

Sample

[M]/[Al]/[NOct4Br]

Time (h)

Conversion %

Yield %

polyEPCH 100

100/1/1

12

0

0

polyEPCH 100

100/1.5/1

12

100

88

polyEPCH 200

100/2.0/1

12

100

87

polyEPCH 500

100/2.7/1

12

100

90

a: [M], [Al] and [NOct4Br] represented molar concentration of EPCH, i-Bu3Al and
NOct4Br respectively.

NMR spectroscopy was used to examine the chemical structures of polyEPCH
1

and polyGBIMTFSI. Figure 2.1 showed the H NMR spectra of polyEPCH with
monomer to initiator ratio of 500 to 1 and the corresponding polyGBIMTFSI.
There were two broad peaks shown in Figure 2.1a, one larger peak with
chemical shift from 3.80 to 3.66 ppm and a smaller peak at 3.66-3.59 ppm. The

71 
 

integration ratio of the two peaks was 4 to 1. The peaks were assigned according
to gHSQC spectrum, shown in Figure 2.2. The peak at 44 ppm in

13

C spectrum

1

correlated to two separate protons in H NMR, and was assigned to the C in
CH2Cl group. The peak at around 70 ppm in
in CH2O group. The peak at 79 ppm in

13

C spectrum was assigned to the C

13

C spectrum was assigned to the C in
1

CHO group. Based on the gHSQC spectrum, the larger peak in H NMR was
assigned to four protons including CH2O, CHO, and 1H from CH2Cl, and the
smaller peak was assigned to the other proton left in CH2Cl. Figure 2.1b showed
1

the H NMR spectra of polyGBIMTFSI. The three peaks with chemical shift
higher than 7.2 ppm were assigned to the three protons in imidazolium ring,
while the sharper peak ~4.2 ppm and the three peaks below 2.0 ppm were
assigned to the butyl group attached to imidazolium ring. The sharp peak ~3.3
ppm was assigned to the residual water dissolving in DMSO-d6. The rest of the
peaks were from the polyEPCH backbone. For accurate assignment of each
peak, gHSQC spectrum was also done for polyGBIMTFSI. Figure 2.3 shows part
of the gHSQC spectrum, which is related to the peaks from polymer backbone.
The peak at 50 ppm in

13

C spectrum was assigned to the C in CH2 connected to

the imidazolium group. Compared to the corresponding peak in polyEPCH, It was
shifted higher about 5 ppm, which was because of the replacement of Cl with a
1

more electron attracting cationic imidazolium group. In H NMR spectrum, the
chemical shift of peaks for the two protons attached to the C at 50 ppm was also
72 
 

shifted higher, from between 3.5 and 3.7 ppm to 4.0 and 4.4 ppm. The peaks at
67 and 77 ppm in

13

C spectrum were assigned to the C in CH2O and CHO
1

respectively. Based on the gHSQC spectrum, the peaks in H NMR spectrum
were labelled, shown in Figure 2.1 b. Peak 10 represented a CH2 in butyl group
on the imidazolium ring and had a integral of 2.00. While peak 3 and 4
represented one proton from CHO and one proton from CH2O of the polyEPCH
backbone. Peak 3 and 4 had a combined integral of 1.96. By comparing the
integrals of peak 10 and peak 3, 4, and taking consideration of integration error,
we can conclude that the quaternarization was quantitative.

 

73 
 

2,3,4,5

1

1.00
4.03

7.00

6.50

6.00

4,5
O
7
8

7 8

3.50 

1 2

1, 2, 9

N 1,2
nTFSI
N 6

3 ,4

10

11

5

1 0

1 1

12

6.0

5.0

4.0

3.0

2.0

3.00
2.02

7.0

2.00

4.02

8.0

4.00

n

0.98
1.01

0.98

9.0

4.50

1.67

6

3

5.00

1.96

9

5.50

1.0

 

δ (ppm)
1

Figure 2.1. H NMR of polyEPCH with monomer to initiator ratio 500/1 (2.1a, top,
CDCl3 as solvent) and the corresponding polyGBIMTFSI (2.1b, bottom, DMSOd6 as solvent).
74 
 

Figure 2.2. gHSQC of polyEPCH with monomer to initiator ratio 500/1. For
interpretation to the references to color in this and all other figures, the reader is
referred to the electronic version of this dissertation.

75 
 

Figure 2.3. gHSQC of polyGBIMTFSI with monomer to initiator ratio 500/1
GPC was used to investigate the molecular weight of polyEPCH synthesized. In
Figure 2.4, GPC traces of polyEPCH with monomer to initiator ratio of 100/1,
200/1 and 500/1 were displayed. From left to right, curves were for polyEPCH
500, polyEPCH 200 and polyEPCH 100 respectively. As shown in Table 2.1,
polyEPCH with different molecular weight was synthesized and all three samples
76 
 

4

showed a low PDI, which was around 1.16. The highest Mn was 7.62 x 10 g/mol
obtained in the case of polyEPCH 500.The Mn obtained by GPC was around two
times of the theoretical values, which was due to the use of polystyrene (PS) as
standard in GPC, since PS and polyEPCH have very different chemical structure
and at the same molecular weight, PS has a much larger hydrodynamic volume
compared to polyEPCH in DMF solution. To get more reasonable molecular
weight data, PEO which has a similar chemical structure as polyEPCH was also
used as GPC standard, with the data shown in Table 2.2. In this case, the GPC
data was smaller than theoretical value. This was attributed to the difference in
hydrodynamic volumes as well. GPC characterization for polyGBIMTFSI did not
provide satisfactory data because the elution would be delayed, which was most
likely due to the strong interaction between ions of polyGBIMTFSI and the
stationary phases. However, thanks to the quantitative quaternarization, the
molecular weight of polyGBIMTFSI can be roughly calculated based on that of
polyEPCH.

77 
 

 
Figure 2.4. GPC traces of polyEPCH with different monomer to initiator ratio.
PolyEPCH 100, 200, 500 means polyEPCH with [M]/[I] = 100, 200 and 500
respectively. DMF was used as solvent at 50 oC and polystyrene was used as
standard.

Table 2.2. Number average molecular weight (Mn), Weight average molecular
weight (Mw) and PDI of polyEPCH 100 , 200 and 500 from GPC, PS as standard

Sample

-3

Mn × 10

a

-3

Mn × 10

b

-3

Mw × 10

PDI

b

b

g/mol

g/mol

g/mol

polyEPCH100

9.3

21.6

25.1

1.16

polyEPCH200

18.5

37.8

42.7

1.13

polyEPCH500

46.3

76.2

89.9

1.18

a: Theoretical value, calculated by [Monomer]/[Initiator] x 92.5 g/mol.
b: data from GPC, PS standard.
78 
 

Table 2.3. Number average molecular weight (Mn), Weight average molecular
weight (Mw) and PDI of polyEPCH 100 , 200 and 500 from GPC, PEO as
standard

Sample

-3

Mn × 10

a

-3

Mn × 10

b

-3

Mw × 10

PDI

b

b

g/mol

g/mol

g/mol

polyEPCH100

9.3

6.3

8.1

1.29

polyEPCH200

18.5

11.8

15.0

1.27

polyEPCH500

46.3

28.2

36.4

1.29

a: Theoretical value, calculated by [Monomer]/[Initiator] x 92.5 g/mol.
b: data from GPC, PEO standard.

FT-IR spectra of polyEPCH500 and the corresponding polyGBIMTFSI500 were
shown in Figure 2.5. To confirm the successful synthesis of polyGBIMTFSI, FTIR spectra of LiTFSI and 1-butylimidazole were also measured. In polyEPCH
spectrum, peaks between 3000 and 2800, peak at 1120 and peak at 748 cm-1
3

were assigned to sp C-H stretching, C-O-C and CH2-Cl stretching respectively,
which was consistent with the

structure of polyEPCH. In polyGBIMTFSI

spectrum, peaks between 3200 and 3100 cm-1 were assigned to the C-H···F
hydrogen bonding bands between hydrogen atoms in imidazolium ring and
-

fluorine atoms in TFSI anion.30 In addition, peaks between 3100 and 3000 cm-1
2

were assigned to sp

C-H stretching, which were absent in polyEPCH, but

present in 1-butylimidazole. This observation provided direct evidence for the
successful synthesis of polyGBIMTFSI. There were other evidence too. Peak at
79 
 

1566 cm-1 was assigned to C=N stretching, also absent in polyEPCH. This peak
(1508 cm-1) existed in FT-IR spectrum of 1-butylimidazole, though it was shifted
higher due to the quaternarization reaction. Other peaks at 1350, 1188, 1136 cm
1

were assigned to SO2 asymmetric, C-F and SO2 symmetric

-

stretching

-

respectively, which supports the existence of TFSI counterion.

Figure 2.5. FT-IR of LiTFSI, butylimidazole, polyEPCH 500 and the
corresponding polyGBIMTFSI500

 

80 
 

Thermal analysis of polyEPCH and polyGBIMTFSI samples
The thermal stability of polyEPCH and polyGBIMTFSI was studied by TGA.
Figure 2.4 showed the TGA traces of polyEPCH with monomer to initiator ratio of
500 to 1 and the corresponding polyGBIMTFSI. Both samples were heated to
120

o

C and held for 30 minutes before proceeding heating to ensure all

physically adsorbed water was removed. As shown in Figure 2.6, polyGBIMTFSI
showed excellent thermal stability with thermal degradation temperatures above
375 oC. On the other hand, polyEPCH showed relatively poor thermal stability
which started to lose weight at ~ 200

o

C. PolyEPCH100, 200 and

polyGBIMTFSI100, 200 also showed similar degradation patterns.

 
Figure 2.6. Normalized TGA traces of polyEPCH with [M]/[I] 500 and the
corresponding polyGBIMTFSI.
81 
 

DSC was used to study the glass transition temperature (Tg) change of
polyEPCH

with

increasing

molecular

weight

and

the

corresponding

polyGBIMTFSI. Figure 2.7 and Table 2.4 showed the results from DSC
measurements. PolyEPCH was a colorless liquid. With the increase of molecular
weight, the Tg increased too. PolyEPCH100 had a Tg of - 36

o

C, while

polyEPCH200 and 500 had a Tg of - 30 and - 28 oC respectively. Compared to
the Tg difference between polyEPCH100 and 200, the difference between
polyEPCH200 and 500 was much smaller. It seemed that the Tg of polyEPCH
had reached a plateau as the molecular weight increased, which was also
confirmed in the case of polyGBIMTFSI. As shown in Table 2.4, after
quaternarization, polyGBIMTFSI showed a higher Tg compared to polyEPCH.
However, the Tg of polyGBIMTFSI with different molecular weight was almost the
same. PolyGBIMTFSI100, 200 and 500 had Tg of -14, -13 and -12 oC
respectively,

which confirmed the plateau formation as the molecular weight

increased. One point worth to mention was that there was no crystallization
region in all polyGBIMTFSI samples, which was preferred as a potential
electrolyte material. Due to the same structure and very close Tg, similar
conductivity would be expected for polyGBIMTFSI100, 200 and 500, which was
confirmed in the conductivity measurement.

82 
 

 
Figure 2.7. DSC curves of polyEPCH100, 200 and 500 and the corresponding
polyGBIMTFSI. From top to bottome, curves are for polyEPCH100, 200, 500 and
polyGBIMTFSI100, 200, 500 respectively.

Table 2.4. Tg of polyEPCH and polyGBIMTFSI with different monomer to initiator
ratio
Sample

Tg / oC

polyEPCH100

-36

polyEPCH200

-30

polyEPCH500

-28

polyGBIMTFSI100

-14

polyGBIMTFSI200

-13

polyGBIMTFSI500

-12

83 
 

Ionic conductivity and viscosity measurement
Ionic conductivity of polyGBIMTFSI over a temperature range from 30 to 90 oC
was measured, as shown in Figure 2.8. The logarithm of conductivity of
polyGBIMTFSI decreased linearly against increase of 1000/T, which can be well
explained by the Arrhenius equation. However, slight convex curvatures in Figure
2.8 suggested that the ion conduction mechanism in polyGBIMTFSI should be
the same as that of general solid polymer electrolytes. This suggests migration of
ions in highly viscous matrix,

31

and the empirical Vogel-Fulcher-Tammann (VFT)

equation would provide a better fitting, as shown in Equation 1,

 B 
 T T 

0


     exp 

(1)

where   is the infinite temperature conductivity, B is a fitting parameter related
to the activation energy of ion conduction, and T0 is the Vogel temperature where
ion motion first occurs (T0 = Tg - 50 K). For polyGBIMTFSI 100, the obtained
values for these fitting parameters are   = 3.25 S/cm, B = 1500 K, T0 = 191 K,
and the corresponding Tg is 241K, which is in good accordance with the Tg (259
K) obtained by DSC measurement. PolyGBIMTFSI with different molecular
weight showed similar conductivity, especially at high temperatures. This can be
explained by the fact that all three polyGBIMTFSI samples had the same
repeating units and very close Tgs. At 30 oC, polyGBIMTFSI 100 showed a
84 
 

-5

conductivity of 1.2 x 10

S/cm, while polyGBIMTFSI 200 and 500 showed
-6

conductivity of around 8.1 x 10

-6

and 5.3 x 10

S/cm. However, as the

temperature increases, the difference of conductivity between different samples
gets smaller. At 90 oC, all samples showed almost identical conductivity, which
was around 8.5 x 10

-4

S/cm.

Figure 2.8. Temperature dependence of ionic conductivities for polyGBIMTFSI
100, 200 and 500.

The viscosities of polyGBIMTFSI were also measured. As shown in Figure 2.9,
the viscosities of polyGBIMTFSI almost followed the opposite trend observed for
conductivity, which indicated that the conducting species in PIL was restricted as

85 
 

the viscosity increased. All three polyGBIMTFSI samples showed high viscosities.
For example, at 32 oC, polyGBIMTFSI showed a viscosity of around 4000 Pa·s,
making it almost cannot flow at all. As electrolyte materials, such a high viscosity
is very beneficial in fabrication process. The viscosity increased with higher
molecular weight and dropped at higher temperature. However, at 90

o

C,

polyGBIMTFSI 500 still showed a high viscosity around 80 Pa·s, which was
80,000 times higher compared to that of water at 20 oC

 
Figure 2.9. Temperature dependence of viscosities of polyGBIMTFSI 100, 200
and 500.

86 
 

Conclusion
A novel family of polyEPCH based PIL electrolytes have been synthesized and
characterized. The PILs obtained showed not only low Tg, high conductivity and
good thermal stability, but also a high viscosity, which is beneficial in fabricating
process. All these properties make this kind of PIL promising electrolyte materials
in electrochemical devices such as lithium battery and dye sensitized solar cell.
It has also been revealed that with the increase of molecular weight, the viscosity
of PILs increased. But the conductivity did not drop much. At high temperatures,
PILs with different molecular weight showed almost identical conductivity.
Currently, a copolymer of PIL and PEO derivative is being studied, which shows
a conductivity of over 10 times higher compared to PIL homopolymer.

87 
 

Experimental section
Materials
Unless otherwise specified, all chemicals and solvents were ACS reagent grade
and used as received from commercial suppliers without further purification.
Epichlorohydrin (EPCH, 99%, Aldrich) was purified over CaH2, distilled under
vacuum and stored in a glove box until use. 1-Butylimidazole was distilled under
vacuum and stored in refrigerator. Toluene was dried by refluxing with sodium pbenzylphenol, distilled under N2 protection and stored in glove box until use.
Triisobutylaluminium (i-Bu3Al) (1 mol/L in toluene, Aldrich), tetraoctylammonium
bromide (NOct4Br, 98%, Aldrich) and lithium bis(trifluoromethanesulfonyl)imide
(LiTFSI, >98%, TCI) were kept in a glove box and used without further
purification.
Synthesis of polyepichlorohydrin (polyEPCH) with monomer to initiator
molar ratio from 100 to 500
24

PolyEPCH was synthesized according to a literature procedure . All
polymerizations were performed between -30 oC and room temperature under
N2 protection in Schlenk flasks. For instance, polyEPCH with monomer to
initiator molar ratio 100 (polyEPCH 100) was synthesized as follows. In a glove
box, epichlorohydrin (EPCH, 10.2 g, 0.11 mol) was dissolved in dry toluene (40
mL) in a 200 mL Schlenk flask, followed by addition of initiator NOct4Br (0.61 g,

88 
 

-3

1.1x10

mol). The solution was then taken out of the glove box and stirred in a

liquid nitrogen/xylene mixture bath under N2 protection for 15 minutes to cool to 30 oC. Catalyst i-Bu3Al (1.7 mL, 1 mol/L in toluene) was added via a syringe.
Reaction started immediately. Polymerization was stopped after 12 h by adding a
few drops of ethanol. PolyEPCH was purified as follows. Toluene was removed
first with a rotavap. The resulting residue was washed with acidic ethanol solution
(3 vol% of HCl in EtOH). The ethanol solution was decanted and the residue was
washed with Milli-Q water until pH was neutral. The product was dissolved in
acetone, filtered to remove undissolved salts, and dried at 50 oC in vacuo
overnight. PolyEPCH with different molecular weight was synthesized by tuning
the monomer to initiator molar ratio, and the amount of catalyst i-Bu3Al.
1

PolyEPCH obtained was a transparent, colorless liquid. Yield: 9.0 g, 88 %. H
NMR (CDCl3, 500 MHz) δ 3.78 - 3.66 (4H), 3.66 - 3.59 (1H).

Synthesis of poly(1-glycidyl-3-butylimidazolium chloride) (polyGBIMCl)
PolyGBIMCl was synthesized by quarternization of polyEPCH with 1butylimidazole. PolyEPCH (9.3 g, 0.1 mol for its repeating unit) was first added
into a 100 mL Schlenk flask, followed by addition of 1-butylimidazole (37.2 g, 0.3
mol) and a magnetic stir bar. The mixture was stirred until homogeneous. 1Butylimidazole was used both as reactant and solvent in this case. The solution
was degassed with the freeze-pump-thaw procedure three times, then inserted
into an oil bath at 115 oC, and refluxed under N2 overnight. In the end, product
precipitated out from 1-butylimidazole solution and stayed in the bottom.
89 
 

PolyGBIMCl was purified as follows. The top 1-butylimidazole layer was
decanted first. The residue was then dissolved in chloroform and precipitated
from ethyl ether. Unreacted polyEPCH and 1-butylimidazole dissolved in ethyl
ether while polyGBIMCl did not. The product was dried by heating at 100 oC in
vacuo. PolyGBIMCl was a highly hygroscopic solid at room temperature. Yield:
1

20.6 g, 95 %. H NMR (CDCl3, 500 MHz) δ 10.46 - 10.32 (1H), 8.36 - 8.22 (1H),
7.82 - 7.56 (1H), 4.94 - 3.58 (7H), 1.96 - 1.82 (2H), 1.42 - 1.30 (2H), 0.98 - 0.86
(3H).
Synthesis

of

poly(1-glycidyl-3-butylimidazolium

bis(trifluoromethanesulfonyl)imide) (polyGBIMTFSI)
PolyGBIMTFSI was obtained by an ion exchange reaction. PolyGBIMCl (10.8 g,
0.050 mol for its repeating unit )was dissolved in 100 mL water, which was
followed by addition of excess amount of LiTFSI (21.5 g, 0.075 mol). The
reaction mixture immediately turned milky. The product was precipitated out by a
30 min centrifugation. PolyGBIMTFSI was purified by washing with Milli-Q water
three times and then dried at 100 oC in vacuo overnight. polyGBIMTFSI was a
1

highly viscous, transparent liquid with a pale yellow color. Yield: 22.6 g, 98 %. H
6

NMR (d -DMSO, 500 MHz) δ 9.08 - 8.96 (1H), 7.87 - 7.78 (1H), 7.63 - 7.49 (1H),
4.44 - 4.00 (4H), 3.82 - 3.54 (2H), 3.34- 3.04 (1H), 1.82 - 1.68 (2H), 1.30 - 1.17
(2H), 0.92 - 0.80 (3H).

90 
 

Characterization
The

1

H and

13

C NMR spectra were recorded with an Varian UnityPlus-500

spectrometer in CDCl3 or DMSO-d6 at room temperature using the residual
solvent proton signals as chemical shift standards. FT-IR spectra were recorded
from a Mattson Galaxy 300 spectrometer purged with dry nitrogen, with signal
-1

averaging 128 scans at a resolution of 4 cm . All IR samples were dried before
measurement. Polymer molecular weight was measured by gel permeation
chromatography (GPC) at 35 °C using two PL-gel 10μm mixed-B columns in
series. DMF was used as eluting solvent at a flow rate of 1 mL/min and Waters
2410 differential refractometer as detector. Mono-dispersed polystyrene or
poly(ethylene oxide) was used as standard to calibrate molecular weight.
Thermogravimetric analyses (TGA) was performed using a Perkin-Elmer TGA 7
instrument at a heating rate of 10 °C/min in the temperature range of 30 °C to
850 °C under air atmosphere. TGA samples were dried in vacuo overnight prior
to use. After increasing the temperature to 120 °C , samples were held in the
TGA apparatus for 30 min before proceeding the heating. Differential scanning
calorimetry (DSC) measurements were performed on a TA DSC Q100 instrument
at a heating/cooling rate of 10 °C/min under nitrogen. Temperature dependent
shear viscosity measurement was carried out in a TA orchestrator rotational
rheometer, version v7.2.0.2, over a temperature range of 30 °C to 90 °C, with a
temperature increasing rate of 2 °C/min and rotation frequency of 10 rad/s.

91 
 

Ionic conductivity measurements
Ionic conductivity measurement were carried out in a home-made cell by
impedance spectroscopy measurements on a AC impedance analyzer HP 4192A
over the frequency range of 5Hz to 13 MHz with an applied voltage of 10 mV.
The sample cell contains two steel disks which serve as symmetric electrodes
and separated by a Teflon collar. All samples were equilibrated at a predetermined temperature for 15 minutes before measurement. The resistance of
the sample was estimated from Nyquist plot, and then the conductivity of the
sample was calculated using the electrodes distance and cell cross-sectional
area, as shown in equation 2:

                            



L
                          (2)
R A

where σ is the ionic conductivity of the sample, L represents the distance
between two electrodes, A stands for the cell cross-sectional area, and R is the
bulk resistance of the sample estimated from Nyquist plot.

92 
 

REFERENCES

93 
 

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Ohno, H.; Ito, K.: Room-temperature molten salt polymers as a matrix for
fast ion conduction. Chem Lett 1998, 751-752.
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Yoshizawa, M.; Ohno, H.: Molecular brush having molten salt domain for
fast ion conduction. Chem Lett 1999, 889-890.
(3)
Ohno, H.: Molten salt type polymer electrolytes. Electrochim Acta 2001, 46,
1407-1411.
(4)
Yoshizawa, M.; Ohno, H.: Synthesis of molten salt-type polymer brush and
effect of brush structure on the ionic conductivity. Electrochim Acta 2001, 46,
1723-1728.
(5)
Washiro, S.; Yoshizawa, M.; Nakajima, H.; Ohno, H.: Highly ion
conductive flexible films composed of network polymers based on polymerizable
ionic liquids. Polymer 2004, 45, 1577-1582.
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Green, O.; Grubjesic, S.; Lee, S. W.; Firestone, M. A.: The Design of
polymeric ionic liquids for the preparation of functional materials. Polym Rev
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(7)
Yuan, J. Y.; Antonietti, M.: Poly(ionic liquid)s: Polymers expanding
classical property profiles. Polymer 2011, 52, 1469-1482.
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Mecerreyes, D.: Polymeric ionic liquids: Broadening the properties and
applications of polyelectrolytes. Prog Polym Sci 2011, 36, 1629-1648.
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Döbbelin, M.: Synthesis of pyrrolidinium-Based poly(ionic liquid)
electrolytes with poly(ethylene glycol) side chains. Chem Mater 2012, 24, 15831590.
(10) Yu, B.; Zhou, F.; Wang, C. W.; Liu, W. M.: A novel gel polymer electrolyte
based on poly ionic liquid 1-ethyl 3-(2-methacryloyloxy ethyl) imidazolium iodide.
Eur Polym J 2007, 43, 2699-2707.

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(11) Zhao, J.; Shen, X. J.; Yan, F.; Qiu, L. H.; Lee, S. T.; Sun, B. Q.: Solventfree ionic liquid/poly(ionic liquid) electrolytes for quasi-solid-state dye-sensitized
solar cells. J Mater Chem 2011, 21, 7326-7330.
(12) Tang, J. B.; Tang, H. D.; Sun, W. L.; Plancher, H.; Radosz, M.; Shen, Y.
Q.: Poly(ionic liquid)s: a new material with enhanced and fast CO2 absorption.
Chem Commun 2005, 3325-3327.
(13) Tang, J. B.; Tang, H. D.; Sun, W. L.; Radosz, M.; Shen, Y. Q.: Poly(ionic
liquid)s as new materials for CO2 absorption. J Polym Sci Pol Chem 2005, 43,
5477-5489.
(14) Bara, J. E.; Lessmann, S.; Gabriel, C. J.; Hatakeyama, E. S.; Noble, R. D.;
Gin, D. L.: Synthesis and performance of polymerizable room-temperature ionic
liquids as gas separation membranes. Ind Eng Chem Res 2007, 46, 5397-5404.
(15) Bara, J. E.; Hatakeyama, E. S.; Gin, D. L.; Noble, R. D.: Improving CO2
permeability in polymerized room-temperature ionic liquid gas separation
membranes through the formation of a solid composite with a room-temperature
ionic liquid. Polym Advan Technol 2008, 19, 1415-1420.
(16) Yan, F.; Texter, J.: Solvent-reversible poration in ionic liquid copolymers.
Angew Chem Int Edit 2007, 46, 2440-2443.
(17) Huang, J.; Tao, C. A.; An, Q.; Zhang, W. X.; Wu, Y. G.; Li, X. S.; Shen, D.
Z.; Li, G. T.: 3D-ordered macroporous poly(ionic liquid) films as multifunctional
materials. Chem Commun 2010, 46, 967-969.
(18) Stancik, C. M.; Lavoie, A. R.; Schutz, J.; Achurra, P. A.; Lindner, P.; Gast,
A. P.; Waymouth, R. M.: Micelles of imidazolium-functionalized polystyrene
diblock copolymers investigated with neutron and light scattering. Langmuir 2004,
20, 596-605.
(19) Yuan, J. Y.; Schlaad, H.; Giordano, C.; Antonietti, M.: Double hydrophilic
diblock copolymers containing a poly(ionic liquid) segment: Controlled synthesis,
solution property, and application as carbon precursor. Eur Polym J 2011, 47,
772-781.
(20) Ohno, H.; Yoshizawa, M.; Ogihara, W.: Development of new class of ion
conductive polymers based on ionic liquids. Electrochim. Acta 2004, 50, 255-261.
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(21) Ricks-Laskoski, H. L.; Snow, A. W.: Synthesis and electric field actuation
of an ionic liquid polymer. J Am Chem Soc 2006, 128, 12402-12403.
(22) Juger, J.; Meyer, F.; Vidal, F.; Chevrot, C.; Teyssie, D.: Synthesis,
polymerization and conducting properties of an ionic liquid-type anionic monomer.
Tetrahedron Lett 2009, 50, 128-131.
(23) Dobbelin, M.; Azcune, I.; Bedu, M.; de Luzuriaga, A. R.; Genua, A.;
Jovanovski, V.; Cabanero, G.; Odriozola, I.: Synthesis of pyrrolidinium-based
poly(ionic liquid) electrolytes with poly(ethylene glycol) side chains. Chem Mater
2012, 24, 1583-1590.
(24) Carlotti, S.; Labbe, A.; Rejsek, V.; Doutaz, S.; Gervais, M.; Deffieux, A.:
Living/controlled anionic polymerization and copolymerization of epichlorohydrin
with tetraoctylammonium bromide-Triisobutylaluminum initiating systems.
Macromolecules 2008, 41, 7058-7062.
(25) Nagasaki, Y.; Kutsuna, T.; Iijima, M.; Kato, M.; Kataoka, K.; Kitano, S.;
Kadoma, Y.: Formyl-ended heterobifunctional poly(ethylene oxide) - Synthesis of
poly(ethylene oxide) with a formyl group at one end and a hydroxyl group at the
other end. Bioconjugate Chem 1995, 6, 231-233.
(26) Rieger, J.; Coulembier, O.; Dubois, P.; Bernaerts, K. V.; Du Prez, F. E.;
Jerome, R.; Jerome, C.: Controlled synthesis of an ABC miktoarm star-shaped
copolymer by sequential ring-opening polymerization of ethylene oxide, benzyl
beta-malolactonate, and epsilon-caprolactone. Macromolecules 2005, 38, 1065010657.
(27) Biedron, T.; Kubisa, P.; Penczek, S.: Polyepichlorohydrin diols free of
cyclics - synthesis and characterization. J Polym Sci Pol Chem 1991, 29, 619628.
(28) Kubisa, P.; Penczek, S.: Cationic activated monomer polymerization of
heterocyclic monomers. Prog Polym Sci 1999, 24, 1409-1437.
(29) Francis, A. U.; Venkatachalam, S.; Kanakavel, M.; Ravindran, P. V.; Ninan,
K. N.: Structural characterization of hydroxyl terminated polyepichlorohydrin
obtained using boron trifluoride etherate and stannic chloride as initiators. Eur
Polym J 2003, 39, 831-841.
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(30) Ries, L. A. S.; do Amaral, F. A.; Matos, K.; Martini, E. M. A.; de Souza, M.
O.; de Souza, R. F.: Evidence of change in the molecular organization of 1-nbutyl-3-methylimidazolium tetrafluoroborate ionic liquid solutions with the addition
of water. Polyhedron 2008, 27, 3287-3293.
(31) Ogihara, W.; Washiro, S.; Nakajima, H.; Ohno, H.: Effect of cation
structure on the electrochemical and thermal properties of ion conductive
polymers obtained from polymerizable ionic liquids. Electrochim. Acta 2006, 51,
2614-2619.

97 
 

Chapter 3 Synthesis and characterization of novel low Tg poly(ionic liquids)
random copolymers
Introduction
In Chapter 2, a series of poly(ionic liquids) based on polyepichlorohydrin
(polyEPCH) have been synthesized. Among them, polyGBIMTFSI 100 had the
-5

highest ionic conductivity, which was 1.2 x 10

S/cm at 30 oC. However,

compared to that of 1-methyl-3-propylimidazolium iodide (PMII), a commonly
used ionic liquid, the conductivity was still two orders of magnitude lower. It was
well known that lower glass transition temperature (Tg) leads to higher
conductivity.

1-3

One way to reduce the Tg of polymers was to introduce another
4,5

low Tg component to the polymer backbone, i.e., forming copolymers.

Elabd

and coworkers studied the effect of introducing a low Tg component on the ionic
5

conductivity of PILs. The copolymer was made by free radical polymerization of
a nonionic monomer n-hexyl methacrylate (HMA) and an ionic monomer 1-(2methacryloyl)ethyl)-3-butylimidazolium tetrafluoroborate (MEBIMBF4). A series of
copolymers with different composition of HMA were obtained by tuning the HMA
concentration in the free radical polymerization. The results indicated that the Tg
of the copolymer decreased with the increase of the HMA composition, and the
conductivity increased correspondingly. In this report, the second component
chosen for copolymer synthesis was a PEO analogue. PEO is synthesized by
polymerization of ethylene oxide and has a Tg ranging from -50 to -57 oC.
98 
 

However, ethylene oxide is a gas at room temperature, making it hard to handle
at regular polymerization conditions. For this reason, an liquid analogue of
ethylene

oxide,

2-((2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methyl)oxirane

(ME3MO), was synthesized. Unlike the synthesis of polyEPCH, the random
copolymer polyEPCH-co-polyME3MO was synthesized by cationic ring-opening
polymerization via activated monomer mechanism using trifluoroborate etherate
and 1,4-butandediol as initiator, Scheme 3.1.

6

After quaternarization and ion

exchange reaction, the PIL copolymer showed a conductivity of more than one
order of magnitude higher compared to that of PIL homopolymer.

Scheme 3.1. Mechanism for trifluoroborate etherate and 1,4-butanediol initiated
cationic polymerization of epichlorohydrin.

99 
 

Results and discussion

Synthesis of polyGBIMTFSI-co-polyME3MO
The

synthesis

of

2-((2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methyl)oxirane

(ME3MO) was shown in Scheme 3.2. Triethylene glycol monomethyl ether was
deprotonated by sodium hydride first and then reacted with epichlorohydrin
(EPCH). The product ME3MO was obtained in a 71 % yield and characterized by
1

1

H NMR, shown in Figure 3.1. The easiest peak to assign in H NMR was peak 7.

It was assigned to the CH3 group in the end of PEO oligomer chain, due to its
1

distinct chemical shift and integral of 3.03. The rest peaks in H NMR were
assigned according to gHSQC and gHMBC (Figure 3.2 and 3.3). From gHSQC,
most of the peaks could be assigned except peak 6. The peak at 44 ppm in

13

C

spectrum was assigned to the C in CH2O group of the oxirane ring. The peak at
51 ppm in

13

C spectrum was assigned to the C in CHO group of the oxirane ring.

The peak at 72 ppm in

13

C spectrum was assigned to the C in CH2O group next

to the oxirane ring. Based on the correlation between the carbons and protons,
1

the peaks from 1 to 5 in H NMR were assigned. The peak 6 was assigned
according to gHMBC. Because the protons of peak 6 interacted with the carbon
of peak 7, peak 6 was assigned to the protons attached to the C closest to the

100 
 

peak 7 in
1

13

C spectrum. In the end, the broad peak with an integral of 10.66 in

H NMR was assigned to the rest five CH2 protons in the PEO oligomer chain.

Scheme 3.2. Synthesis of ME3MO

101 
 

7

8

3

4

2.11

3.03
1.00

0.86

1.00

10.66

1.05

2

3.50

3.00

1

Figure 3.1. H NMR of ME3MO

102 
 

5

0.95

6

1

2.50

Figure 3.2. gHSQC of ME3MO

103 
 

Figure 3.3. gHMBC of ME3MO

The polyEPCH-co-polyME3MO was synthesized by cationic ring-opening
polymerization using BF3OEt2 and 1,4-butanediol as initiator, instead of the
initiators in anionic one used in Chapter 2 using i-Bu3Al and NOct4Br. This is
because in anionic ring-opening polymerization, the amount of i-Bu3Al added
must be precisely controlled to achieve high molecular weight product. For
example, the molecular weight of polyEPCH synthesized using different i-

104 
 

Bu3Al/NOct4Br ratio was shown in Table 3.1. When [M]/[Al]/[NOct4Br] equals to
100/1/1, no polymerization happened. When [M]/[Al]/[NOct4Br] equals to
100/1.5/1, the highest Mn and lowest PDI was obtained. And further increase of
[M]/[Al]/[NOct4Br] ratio resulted in lower Mn and higher PDI. It was concluded that
increasing i-Bu3Al/NOct4Br ratio had a negative effect on the synthesis of
polyEPCH. On the other hand, the molecular weight of polyME3MO synthesized
using different i-Bu3Al/NOct4Br ratio was shown in Table 3.2. Increasing iBu3Al/NOct4Br ratio generally increased the Mn of polyME3MO. However, in all 5
samples, the Mn of polyME3MO was very low compared to the theoretical value
calculated by the monomer to initiator ratio. Based on the data in Table 3.1 and
3.2, the anionic ring-opening polymerization using i-Bu3Al and NOct4Br as
initiator was not suitable for the synthesis of polyEPCH-co-polyME3MO.

105 
 

Table 3.1. Molecular weight of polyEPCH synthesized using different iBu3Al/NOct4Br ratio
a

[M]/[Al]/[NOct4Br]

Mn x
b

g/mol

-3

10

-3

Mw x 10
b

g/mol

-3

Mp x 10

PDI

b

b

g/mol

100/1/1

No polymerization

100/1.5/1

5.7

8.0

8.2

1.40

100/3/1

5.1

11.0

8.7

2.17

100/5/1

2.1

5.0

6.1

2.38

100/10/1

1.6

4.1

5.2

2.56

a: [M], [Al] and [NOct4Br] represented molar concentration of EPCH, i-Bu3Al and
NOct4Br respectively.
b: Mn is the number average molecular weight, Mw is the weight average
molecular weight, Mp is the peak molecular weight and PDI is the polydispersity
index. Data was from GPC, using PEO as standard.

106 
 

Table 3.2. Molecular weight of polyME3MO synthesized using different iBu3Al/NOct4Br ratio
a

[M]/[Al]/[NOct4Br]

Mn x
b

-3

10

-3

Mw x 10
b

-3

Mp x 10

PDI

b

b

g/mol

g/mol

g/mol

100/2/1

1.8

2.3

2.4

1.28

100/3/1

2.4

3.0

3.1

1.25

100/4/1

2.6

3.3

3.4

1.27

100/5/1

2.5

3.3

3.5

1.32

100/10/1

2.7

3.5

3.6

1.30

a: [M], [Al] and [NOct4Br] represented molar concentration of ME3MO, i-Bu3Al
and NOct4Br respectively.
b: Mn is the number average molecular weight, Mw is the weight average
molecular weight, Mp is the peak molecular weight and PDI is the polydispersity
index. Data was from GPC, using PEO as standard.

Cationic ring-opening polymerization was used to synthesize polyEPCH,
polyME3MO and polyEPCH-co-polyME3MO, as shown in Scheme 3.3. Six
copolymer samples with different monomer composition and polyEPCH,
polyME3MO homopolymer were synthesized. The molecular weight data was
3

shown in Table 3.3. PolyEPCH homopolymer had a Mn of 2.2 x 10 g/mol, and
3

polyME3MO homopolymer had a Mn of 3.4 x 10 g/mol. The Mn of copolymer
increased with the increase of polyME3MO composition.

107 
 

Scheme 3.3. Copolymerization
quaternatization

of

EPCH

108 
 

and

ME3MO,

followed

by

Table 3.3. Molecular weight of polyEPCH, polyME3MO and polyEPCH-copolyME3MO synthesized using BF3OEt2 and 1,4-butanediol as initiator.
a

[M]1/[M]2/[diol]/[ BF3OEt2]

Mn

x

-3

10

b

-3

Mw x 10
b

-3

Mp x 10

b

PDI

b

g/mol

g/mol

g/mol

100/0/6/1

2.2

3.3

2.8

1.50

0/100/6/1

3.4

4.8

3.6

1.41

100/12.5/6/1

3.9

5.8

4.0

1.49

100/25/6/1

4.4

6.4

5.0

1.45

100/50/6/1

4.9

7.4

6.0

1.51

100/100/6/1

5.4

8.7

7.1

1.61

100/200/6/1

7.3

11.7

9.4

1.60

100/400/6/1

12.0

19.8

15.4

1.65

a: [M]1, [M]2, [diol] and [BF3OEt2] represented molar concentration of EPCH,
ME3MO, 1,4-butanediol and BF3OEt2 respectively.
b: Mn is the number average molecular weight, Mw is the weight average
molecular weight, Mp is the peak molecular weight and PDI is the polydispersity
index. Data was from GPC, using PEO as standard.

PolyGBIMTFSI-co-polyME3MO

was

synthesized

by

quaternarizing

the

polyEPCH-co-polyME3MO with 1-butylimidazole, and followed by an ion
exchange reaction. Only the polyEPCH component in the copolymer was
quaternarized, while the polyME3MO was left intact. High yield was achieved for
all

samples.

The

structure

of

the

1

polyGBIMTFSI-co-polyME3MO

was

characterized by H NMR, as shown in Figure 3.4. The peaks between 3.0 and

109 
 

4.5 ppm represented protons from the polyGBIMTFSI backbone, all protons from
polyME3MO and one CH2 from butyl group. The three peaks above 7.4 ppm
were assigned to the three protons from imidazolium ring. And the three peaks
below 1.8 ppm were the protons from CH2CH2CH3 of the butyl group on the
imidazolium ring. The integral of CH3 group was set to be 3, and the integral of
broad peaks between 3.0 and 4.5 ppm was 12.23. The integrals corresponded to
the composition of copolymer polyGBIMTFSI-co-polyME3MO-4/1 very well.

5.0

1

4.0

3.0

Figure 3.4. H NMR of polyGBIMTFSI-co-polyME3MO-4/1

110 
 

2.0

3.00

6.0

1.91

7.0

1.95

8.0

12.23

1.90

0.89

9.0

1.0

Thermal analysis of polyGBIMTFSI-co-polyME3MO samples
The thermal stability of polyGBIMTFSI and its random copolymers was studied
by TGA, as shown in Figure 3.5. PolyGBIMTFSI and polyGBIMTFSI-copolyME3MO with higher molar ratio of polyGBIMTFSI (from 8/1 to 2/1) showed
showed excellent and similar thermal stability with thermal degradation
temperatures above 375 oC. One the other hand, polyGBIMTFSI-co-polyME3MO
with higher molar ratio of polyME3MO (from 1/1 to 1/4) showed relatively poor
thermal stability, which started to lose weight at ~ 200 oC. Besides, as shown in
Figure 2.4 in the previous chapter, polyEPCH also started to lose weight at ~ 200
o

C. The thermal stability enhancement of polyGBIMTFSI was from the

quaternarization which replaced the weak bonding between the pending CH2-Cl
or CH2-O(CH2CH2O)3CH3.

111 
 

Figure 3.5. TGA traces of polyGBIMTFSI, polyME3MO and their random
copolymer with varying molar compositionThe glass transition temperatures (Tgs)
of polyGBIMTFSI, polyME3MO and their random copolymers were studied by
DSC. As shown in Table 3.4, polyGBIMTFSI showed the highest Tg (-25
and polyME3MO showed the lowest Tg (-52

o

o

C),

C). All the random copolymers

showed Tgs between them. With higher molar composition of polyME3MO, the
copolymer showed lower Tg.

112 
 

Table 3.4. Tg of the polyGBIMTFSI, polyME3MO and their random copolymers
with varying molar composition.
Sample

Tg / oC

polyGBIMTFSI

-25

polyGBIMTFSI-co-polyME3MO (8/1)

-29

polyGBIMTFSI-co-polyME3MO (41)

-33

polyGBIMTFSI-co-polyME3MO (2/1)

-36

polyGBIMTFSI-co-polyME3MO (1/1)

-41

polyGBIMTFSI-co-polyME3MO (1/2)

-43

polyGBIMTFSI-co-polyME3MO (1/4)

-45

polyME3MO

-52

Ionic conductivity measurement
Ionic conductivities of polyGBIMTFSI and polyGBIMTFSI-co-polyME3MO over a
temperature range from 25 to 90 oC was measured, as shown in Figure 3.6. The
ionic conductivity data agrees well with the Tg data. PolyGBIMTFSI with highest
Tg showed the lowest ionic conductivity. With the increase of the composition of
polyME3MO, the conductivity increased up to polyGBIMTFSI-co-polyME3MO-1/1.
However, at higher compositions of polyME3MO, the conductivity started to
decrease.

PolyGBIMTFSI-co-polyME3MO-1/1

and

polyGBIMTFSI-co-

polyME3MO-1/4 showed lower conductivity compared to their 1/1 analogue. This
113 
 

phenomenon is easy to understand and similar results have been reported in
literature.5 Introduction of polyME3MO lowered the Tg, which had a positive effect
on the ionic conductivity of the copolymer. On the other hand, increasing
polyME3MO

composition

meant

decreasing

polyGBIMTFSI

composition,

resulting in lower concentration of charge carriers, which had a negative effect on
the ionic conductivity of the copolymer. In the beginning, the conductivities of
copolymers increased with the increase of polyME3MO composition, because the
reduction in Tg had a more significant effect on ionic conductivity compared to
the reduction in charge carriers concentration. However, in the case of
polyGBIMTFSI-co-polyME3MO-1/2 and polyGBIMTFSI-co-polyME3MO-1/4, as
the concentration of charge carriers got very low, the negative effect
overwhelmed the positive effect.
PolyGBIMTFSI-co-polyME3MO-1/1 showed the highest conductivity (around 1.2
-4

x 10

S/cm at 25 oC), which was more than 1 order of magnitude higher

compared to that of polyGBIMTFSI homopolymer (9.3 x 10

-6

S/cm at 25 oC). On

the other hand, the conductivity of a commonly used ionic liquid, 1- methyl-3propylimidazolium iodide (MPII), was 1.1 x 10

-3

S/cm at 25 oC (Figure 4.8. in next

chapter). The conductivity of polyGBIMTFSI-co-polyME3MO-1/1 was only less
than 1 order of magnitude lower than that of MPII. Introducing low Tg component

114 
 

to form PIL copolymer proved to be very effective in improving the ionic
conductivity of poly(ionic liquids).

Figure 3.6. Ionic conductivities of polyGBIMTFSI and its random copolymers with
varying molar composition.

Conclusion

2-((2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methyl)oxirane

(ME3MO),

a

liquid

analogue of ethylene oxide, was synthesized and copolymerized with EPCH. The
resulting copolymer (polyEPCH-co-polyME3MO) was quaternarized with 1butylimdazole and followed by an ion exchange reaction to form a PIL copolymer

115 
 

(polyGBIMTFSI-co-polyME3MO). By tuning the monomer composition, a series
of PIL copolymers from polyGBIMTFSI-co-polyME3MO-8/1 to polyGBIMTFSI-copolyME3MO-1/4 were synthesized. All PIL copolymer samples showed higher
ionic conductivity than PIL homopolymer. Among them, polyGBIMTFSI-co-4

polyME3MO-1/1 showed the highest ionic conductivity (around 1.2 x 10

S/cm at

25 oC), which was more than 1 order of magnitude higher than PIL homopolymer
-6

(9.3 x 10

S/cm at 25 oC). On the other hand, the ionic conductivity of a

commonly used ionic liquid, 1- methyl-3-propylimidazolium iodide (MPII), was 1.1
-3

x 10

S/cm at 25 oC. The conductivity of polyGBIMTFSI-co-polyME3MO-1/1 was

only less than 1 order of magnitude lower than that of PMII. Introducing low Tg
component to form PIL copolymer proved to be very effective in improving the
ionic conductivity of PIL.

116 
 

Experimental section
Materials
Unless otherwise specified, all chemicals and solvents were ACS reagent grade
and used as received from commercial suppliers without further purification.
Epichlorohydrin (EPCH, 99%, Aldrich) was purified over CaH2, distilled under
vacuum and stored in a glove box until use. 1-Butylimidazole was distilled under
vacuum and stored in refrigerator. Toluene was dried by refluxing with sodium pbenzylphenol, distilled under N2 protection and stored in glove box until use.
Boron trifluoride diethyl etherate (BF3OEt2) (≥ 46% BF3 basis, Aldrich) and 1,4butanediol (99%, Aldrich) were distilled under N2 protection and stored in golve
box until use. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, >98%, TCI)
were kept in a glove box and used without further purification.
Synthesis

of

2-((2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methyl)oxirane

(ME3MO)
7

ME3MO was synthesized according to a literature method. NaH (60 wt% in
mineral oil, 9 g, 0.23 mol) was rinsed with toluene and added to 200 mL THF.
The triethylene glycol monomethyl ether (32.8 g, 0.2 mol) was then added and
stirred for 2 h. The solution was then cooled to 0 oC in ice bath, and followed by
addition of epichlorohydrin (18.4 g, 0.2 mol) gradually. The solution was stirred at
0

o

C to room temperature overnight. After the reaction, the solution was

117 
 

neutralized with 30 % methanolic H2SO4. The solution was then filtered,
concentrated with a rotavap and distilled under vacuum. The yield was 31.2 g,
1

71 %. H NMR (CDCl3, 500 MHz) δ (ppm) 3.66 (dd, J = 11.7, 3.0 Hz, 1H), 3.61 3.49 (br, 10H), 3.44 - 3.40 (m, 2H), 3.29 (dd, J = 11.7, 5.9 Hz, 2H), 3.25 (s, 3H),
3.05 - 3.00 (m, 1H), 2.66 (dd, J = 5.0, 4.2 Hz, 1H), 2.48 (dd, J = 5.0, 2.7 Hz, 1H).
13

C NMR (CDCl3, 500 MHz) δ (ppm) 71.55, 71.50, 70.28, 70.16 (overlapping

signals), 70.06, 58.50, 50.32, 43.66. MS (TOF MS ES+) calculated for
+

C10H20O5Na (m/z), 243.1208; found, 243.1213.

Synthesis of polyEPCH by cationic ring-opening polymerization.
PolyEPCH was synthesized by cationic ring-opening polymerization according to
a literature method.6 In a dry Schlenk flask, 1,4-butanediol (0.44 g, 4.8 mmol)
was added to 22.5 mL dry toluene. This solution was degassed by freeze-pumpthaw procedure three times and then protected by N2 gas flow. To this solution,
BF3OEt2 (0.12 g, 0.81 mmol) was slowly added under N2 atmosphere and stirred
for 60 mins at room temperature. The solution was cooled to 0 oC in an ice bath,
followed by addition of EPCH (7.5 g, 81 mmol) drop by drop. The polymerization
was stopped after 8 h by adding small amount of distilled water. The polymer
solution was washed with sodium bicarbonate solution (5 % wt/v), followed by
several washings with distilled water until pH neutral. The solvent was removed
by vacuum distillation. The product was then dried under vacuum at 60 oC

118 
 

1

overnight. The yield was 6 g, 80 %. H NMR (CDCl3, 500 MHz) δ 3.78 - 3.66 (4H),
3.66 - 3.59 (1H).

Synthesis of polyME3MO

PolyME3MO was synthesized in the same way as polyEPCH. In a dry Schlenk
flask, 1,4-butanediol (0.44 g, 4.8 mmol) was added to 22.5 mL dry toluene. This
solution was degassed by freeze-pump-thaw procedure three times and then
protected by N2 gas flow. To this solution, BF3OEt2 (0.12 g, 0.81 mmol) was
slowly added under N2 atmosphere and stirred for 60 mins at room temperature.
The solution was cooled to 0 oC in an ice bath, and followed by addition of
ME3MO (17.8 g, 81 mmol) drop by drop. The polymerization was stopped after
18 h by adding small amount of distilled water. The purification method was a
little bit different, since polyME3MO dissolved in water. The polymer solution was
washed with sodium bicarbonate solution (5 % wt/v) first. After that, the polymer
was extracted by CHCl3 and precipitated from hexane. The yield was 13.4 g,
1

75 %. H NMR (CDCl3, 500 MHz) δ 3.74 - 3.22 (20H).

119 
 

Synthesis of polyEPCH-co-polyME3MO random copolymer.

PolyEPCH-co-polyME3MO random copolymer was also synthesized in the same
way as polyEPCH. A series of copolymers were obtained by changing the molar
concentration of

ME3MO monomer, while keeping that of EPCH monomer

constant. For example, polyEPCH-co-polyME3MO random copolymer with 1 to 1
monomer molar ratio (polyEPCH-co-polyME3MO-1/1) was prepared as follows.
In a dry Schlenk flask, 1,4-butanediol (0.44 g, 4.8 mmol) was added to 22.5 mL
dry toluene. This solution was degassed by freeze-pump-thaw procedure three
times and then protected by N2 gas flow. To this solution, BF3OEt2 (0.12 g, 0.81
mmol) was slowly added under N2 atmosphere and stirred for 60 mins at room
temperature. The solution was cooled to 0 oC in an ice bath, and followed by
addition of pre-mixed EPCH (7.5 g, 81 mmol) and ME3MO (17.8 g, 81 mmol)
drop by drop. The copolymer was purified the same way as polyME3MO. The
yield was 18.5 g, 73 %. For copolymers with different monomer molar ratio, the
1

yield varied from 60 % to 80 %. H NMR (CDCl3, 500 MHz) δ 3.66 - 3.44 (22H),
3.39 - 3.36 (3H).

120 
 

Synthesis of polyGBIMTFSI-co-polyME3MO

A series of polyGBIMTFSI-co-polyME3MO were synthesized based on different
polyEPCH-co-polyME3MO samples obtained. PolyGBIMTFSI-co-polyME3MO-1/1
was synthesized as follows. PolyEPCH-co-polyME3MO-1/1 (12.5 g, 40 mmol for
its repeating unit) was first added into a 100 mL Schlenk flask, followed by
addition of 1-butylimidazole (14.9 g, 120 mmol) and a magnetic stir bar. The
mixture was stirred until homogeneous. 1-Butylimidazole was used both as
reactant and solvent again. The solution was degassed with the freeze-pumpthaw procedure three times, then inserted into an oil bath at 115 oC, and refluxed
under N2 overnight. After reaction, the polyGBIMCl-co-polyME3MO polymer was
precipitated from ethyl ether, collected and dried under vacuum for 8 h. The
polymer was dissolved in 100 mL Milli-Q water and followed by addition of
excess amount of LiTFSI (17.2 g, 60 mmol). The polyGBIMTFSI-co-polyME3MO1/1 product was collected by a 30 mins centrifugation, purified by washing with
Milli-Q water three times, and dried at 100 oC in vacuo overnight. The yield was
1

6

23.7 g, 87 %. H NMR (d -DMSO, 500 MHz) δ 9.20 - 8.98 (1H), 7.88 - 7.50 (2H),
4.50 - 3.00 (27H), 1.82 - 1.72 (2H), 1.28 - 1.14 (2H), 0.92 - 0.80 (3H).
Characterization
The

1

H and

13

C NMR spectra were recorded with an Varian UnityPlus-500

spectrometer in CDCl3 or DMSO-d6 at room temperature using the residual
121 
 

solvent proton signals as chemical shift standards. gHSQC and gHMBC 2D NMR
spectra were recorded with  an  Agilent DDR2 500 MHz NMR spectrometer
equipped with 7600AS 96 sample autosamplers. Polymer molecular weight was
measured by gel permeation chromatography (GPC) at 35 °C using two PL-gel
10μ mixed-B columns in series. DMF was used as eluting solvent at a flow rate of
1 mL/min and Waters 2410 differential refractometer as detector. Monodispersed poly(ethylene oxide) was used as standard to calibrate molecular
weight. Thermogravimetric analyses (TGA) was performed using a Perkin-Elmer
TGA 7 instrument at a heating rate of 10 °C/min in the temperature range of
30 °C to 850 °C under air atmosphere. TGA samples were dried in vacuo
overnight prior to use. After increasing the temperature to 120 °C , samples were
held in the TGA apparatus for 30 min before proceeding the heating. Differential
scanning calorimetry (DSC) measurements were performed on a TA DSC Q100
instrument at a heating/cooling rate of 10 °C/min under nitrogen.
Ionic conductivity measurements
Ionic conductivity measurements were carried out in a home-made cell by
impedance spectroscopy measurements on a AC impedance analyzer HP 4192A
over the frequency range of 5 Hz to 13 MHz with an applied voltage of 10 mV.
The sample cell contains two steel disks which serve as symmetric electrodes
and separated by a Teflon collar. All samples were equilibrated at a predetermined temperature for 15 minutes before measurement. The resistance of
the sample was estimated from Nyquist plot, and then the conductivity of the

122 
 

sample was calculated using the electrodes distance and cell cross-sectional
area, as shown in equation 1:



L
                          (1)
R A

where σ is the ionic conductivity of the sample, L represents the distance
between two electrodes, A stands for the cell cross-sectional area, and R is the
bulk resistance of the sample estimated from Nyquist plot.

123 
 

REFERENCES

124 
 

REFERENCES
(1)
Green, O.; Grubjesic, S.; Lee, S. W.; Firestone, M. A.: The design of
polymeric ionic liquids for the preparation of functional materials. Polym Rev
2009, 49, 339-360.
(2)
Mecerreyes, D.: Polymeric ionic liquids: Broadening the properties and
applications of polyelectrolytes. Prog Polym Sci 2011, 36, 1629-1648.
(3)
Yuan, J. Y.; Antonietti, M.: Poly(ionic liquid)s: Polymers expanding
classical property profiles. Polymer 2011, 52, 1469-1482.
(4)
Ye, Y. S.; Choi, J. H.; Winey, K. I.; Elabd, Y. A.: Polymerized ionic liquid
block and random copolymers: Effect of weak microphase separation on ion
transport. Macromolecules 2012, 45, 7027-7035.
(5)
Chen, H.; Choi, J. H.; Salas-de La Cruz, D.; Winey, K. I.; Elabd, Y. A.:
Polymerized ionic liquids: The effect of random copolymer composition on ion
conduction. Macromolecules 2009, 42, 4809-4816.
(6)
Francis, A. U.; Venkatachalam, S.; Kanakavel, M.; Ravindran, P. V.; Ninan,
K. N.: Structural characterization of hydroxyl terminated polyepichlorohydrin
obtained using boron trifluoride etherate and stannic chloride as initiators. Eur
Polym J 2003, 39, 831-841.
(7)
Jungk, S. J.; Moore, J. A.; Gandour, R. D.: Efficient synthesis of C-pivot
lariat ethers - 2-(alkoxymethyl)-1,4,7,10,13,16-hexaoxacyclooctadecanes. J Org
Chem 1983, 48, 1116-1120.
 
 

125 
 

Chapter 4 Direct polymerization of IL monomers from surface of silica
nanopaticles: kinetics, characterization, and application in DSSCs
Introduction:
Because of the possible low production cost and expected high conversion
efficiency, DSSCs have been extensively studied in recent years.

1,2

DSSCs

were usually assembled with liquid electrolytes. The highest conversion
3

efficiency of DSSCs employing liquid electrolytes has exceeded 12 %. However,
for long-term stability consideration, liquid electrolytes must be avoided since the
evaporation of organic solvents would decrease the cell performance. Due to
their negligible volatility, high intrinsic conductivity, good chemical and thermal
stability, ILs have been considered as a promising replacement to liquid
electrolytes.

4,5

However, for material application, the liquid property of ILs presents a great
challenge for sealing and fabrication. To overcome this problem, while keeping
the specific properties of ILs, a new class of hybrid materials called ionogels was
made.

6,7

Ionogels were prepared by hybridizing ILs with another component
8,9

such as organic gelator,

14,15

metal oxide nanoparticles.

10,11

polymer,

carbon nanotubes

12,13

and inorganic

Among these methods, due to their chemical

stability, inorganic nanoparticles are preferred over organic gelators, which can
exhibit secondary reactions in long-term operations.
126 
 

6

Gelation of ILs with

inorganic silica nanoparticles was first studied by Grätzel's group. 5 wt% fumed
silica nanoparticles was hybridized with 1-methyl-3-propylimidazolium iodide
(MPII) and used as the electrolyte in quasi-solid DSSC. Compared to liquid MPII
electrolyte, gel electrolyte not only showed essentially same performance in
power conversion efficiency, but also enabled fabrication of flexible, compact,
14

free-of-leakage DSSCs.

More recently, Watanabe et al. studied the colloidal

stability of PMMA-grafted silica nanoparticles in ILs.

16,17

They found that PMMA-

grafted silica nanoparticles were well stabilized in ILs at low concentrations.
However, when the particle concentration increased to 15 wt% or higher, gelling
material was formed. Archer's group reported a novel class of silica ionogel
formed by dispersing IL-grafted silica nanoparticle in an IL host.

18

They found

that with the addition of appropriate amount of IL-grafted silica nanoparticles, the
host IL's crystallization could be completely suppressed, which opened the way
for facile synthesis of ILs with extended operation temperature range.
Herein, we report a novel ionogel composed by PIL-tethered silica nanoparticle
and

MPII.

Poly(1-(4-vinylbenzyl)-3-butylimidazolium

tetrafluoroborate)

(polyVBBIT) was grown from the surface of silica nanoparticle via atom transfer
radical polymerization (ATRP). ATRP was chosen because it was a
controlled/living polymerization technique, which enabled fine tuning of the
19

polymer chain length on silica particles.

MPII was used in our study because

among the 1,3-dialkylimidazolium iodide compounds, MPII has the lowest
viscosity, and its liquid domain extends down to -55 °C. An ionogel was formed
127 
 

by dispersing polyVBBIT-tethered silica nanoparticle into MPII, heated at 60 °C
for 3h and then cooled to room temperature. The ionogel formed retained high
conductivity, which was only slightly below that of pure MPII. The ionogel
electrolyte was employed in DSSC and a conversion efficiency of 0.37 % was
obtained.

Results and Discussion
Synthesis of 1-(4-vinylbenzyl)-3-butylimidazolium tetrafluoroborate (VBBIT)
Synthesis of VBBIT was shown in Scheme 4.1. 4-Vinylbenzyl chloride was first
quaternarized with 1-butylimidazole to form 1-(4-vinylbenzyl)-3-butyl imidazolium
chloride (VBBICl), a water-soluble hygroscopic wax-like solid. Since the chloride
-

anion (Cl ) in VBBICl had a negative effect on ATRP polymerization,
-

tetrafluoroborate (BF4 ) was introduced by an ion exchange reaction to replace
-

the Cl . VBBICl was dissolved in dry acetone and followed by adding an excess
amount of sodium tetrafluoroborate (NaBF4), and stirring for 3 days at room
temperature. After removing NaCl salt by filtration, followed by rotavap to remove
acetone, a viscous ionic liquid monomer 1-(4-Vinylbenzyl)-3-butyl imidazolium
tetrafluoroborate (VBBIT) was obtained. In both steps, small amount of 2,6-ditert-butyl-4-methylphenol (DBMP) was added to prevent autopolymerization.
After reaction, the crude VBBIT product was washed with water 3 times to
remove all the un-reacted VBBICl and NaBF4 salt. In addition, the residual DBMP
128 
 

was washed away with diethyl ether 3 times. The completion of the ion exchange
reaction was confirmed by silver nitrate test. A small amount of VBBIT was
dissolved in acetone and followed by addition of some silver nitrate salt. After
stirring, no white precipitate was observed. After dring under vacuum at 80 °C
overnight, a viscous IL monomer, VBBIT was obtained. The chemical structure
1

was characterized by H NMR, shown in Figure 4.1.

Scheme 4.1. Synthesis of IL monomer-VBBIT

129 
 

1

Figure 4.1. H NMR of VBBIT, DMSO-d6 as solvent.

130 
 

Surface-Initiated ATRP of VBBIT from silica nanoparticles.
The synthetic route of polyVBBIT/silica nanocomposite is shown in Scheme 4.2.
Colloidal silica (Snowtex-XS, Nissan Chemical Corporation) was received in the
form of an aqueous dispersion in pH 9 ~ 10 water. Cetyltrimethylammonium
bromide (CTAB) was added to precipitate silica nanoparticles from aqueous
dispersion. Figure 4.2 shows FT-IR spectra of precipitated silica particles and
-1

their derivatives. In spectrum a, peaks at 1100 and 800 cm

are assigned to Si-

O-S and Si-OH stretching respectively. In addition, peaks between 3000 and
2800 cm

-1

3

are assigned to sp C-H stretching, which are from the CTAB salt

physically adsorbed on the surface of silica nanoparticles. An ATRP initiator, (11(2-bromo-2-methyl)propionyloxy)undecyltrichlorosilane, was then anchored onto
the silica nanoparticle surface by reacting with silanol groups. In spectrum b, the
-1

peak at 1730 cm , which is assigned to C=O stretching, is a direct evidence for
successfully anchoring initiators onto the silica nanoparticle surface. Finally,
VBBIT was grown from the nanoparticle surface via ATRP in butyronitrile at
90 °C, using N,N,N',N',N"-pentamethyldiethylene triamine (PMDETA) as ligand.
The polyVBBIT/silica nanocomposites were collected by centrifugation and
washed with acetone several times. No polyVBBIT homopolymer was found in
the reaction solution indicated that the polymerization was restricted to the
particle surfaces. In spectrum c, a new peak at 3010 cm
-1

and a broad peak at 1640 cm

2

for sp C-H stretching,

for C=C and C=N stretching, are consistent with

131 
 

-1

successfully growing polyVBBIT on silica nanoparticle surface. For better
comparison, a homopolymer of polyVBBIT was also synthesized via ATRP in
solution. In Figure 4.2, spectrum d for polyVBBIT homopolymer and sprctrum c
for polyVBBIT/silica nanocomposite are very similar, which is another evidence
for successful growth of a thick layer of polyVBBIT on silica nanoparticles.

Scheme 4.2. Synthetic route to polyVBBIT/silica nanocomposites.

132 
 

Figure 4.2. FT-IR spectra of (a) silica nanoparticles, (b) surface initiator, (c)
polyVBBIT/silica nanocomposite, and (d) polyVBBIT homopolymer. Samples
were made into pellets with KBr.

The thermal gravimetric analysis (TGA) data was consistent with the FT-IR data.
As shown in Figure 4.3, silica nanoparticle lost 14 % of the weight at 850 °C,
which was mainly due to the decomposition of cetyltrimethylammonium bromide
(CTAB) salt adsorbed on the nanoparticle surface and structural water release
due to bonded hydroxyl groups. For surface initiator, the weight loss was 18 % at
850 °C. Since part of the CTAB salt would be replaced by the initiator, it was
concluded that more than 4 % of the total weight initiator was anchored to the

133 
 

silica nanoparticle. For polyVBBIT/silica nanocomposites, the weight loss was
78%, which corresponded to a thick layer of polyVBBIT growing on the surface of
nanoparticles. The polyVBBIT homopolymer lost more than 98 % of its weight in
the end. The 2 % residual weight was probably from some remaining copper
salts since it was synthesized via ATRP.

Figure 4.3. TGA data for (a) silica nanoparticles, (b) nanoparticles modified with
surface anchored initiators, (c) polyVBBIT/silica nanocomposites (d) and
polyVBBIT. All samples were run in air and at a heating rate of 10 °C/min.

134 
 

To confirm the surface initiated ATRP of VBBIT was a controlled, living
polymerization, the kinetics of the reaction was studied. Due to the poor solubility
of polyVBBIT/silica nanocomposites in polymerization solution (butyronitrile),
tracking the course of polymerization was difficult. Instead, following monomer
consumption by

1

H NMR was chosen and an internal standard 4,4-

dichlorodiphenyl sulfone was used. 4,4-dichlorodiphenyl sulfone was chosen
because of its similar solubility with VBBIT monomer, non-volatility, and its
distinct proton chemical shifts. Monomer consumption was calculated from the
comparison of the integration of C-H groups (a, 7.98 ppm) in the phenyl ring of
4,4-dichlorodiphenyl sulfone and that of C-H group (b, 6.75 ppm) in VBBIT
monomer (Figure 4.4).

135 
 

1

Figure 4.4. 500 MHz H NMR spectra of a representative sample for kinetic
study of surface initiated ATRP of VBBIT.
136 
 

The polymerization was well-behaved, and when plotted as ln( [M]0/[M]) vs time.
The data approximated a line, which was consistent with a first order reaction up
to 400 mins (Figure 4.5).

Figure 4.5. Kinetic study of surface initiated ATRP of VBBIT, the concentration
ratio of [M]0 : [Si-Ini] : [CuBr] : [PMDETA] is approximately 100 : 1 : 2 : 6. [M]0
and [M] represent the initial concentration of VBBIT monomer and the
concentration of monomer at specific time.

The sizes of dried Snowtex-XS silica nanoparticles and polyVBBIT/silica
nanocomposites were studied by Transmission Electron Microscopy (TEM)
137 
 

(Figure 4.6.). The colloidal silica nanopaticles in aqueous solution have a
diameter of 7 nm. However, after precipitating from solution by adding CTAB
salts, the particles aggregated. The diameters of aggregates varied from 20 nm
to 80 nm. After growing a thick layer of polyVBBIT on silica surface, the particles
were better dispersed. In Figure 4.6 b, the dark spots were cores of silica
nanoparticles, while the gray part was the polymer on the surface of
nanoparticles.

138 
 

Figure 4.6. TEM images of dried Snowtex-XS nanoparticles (a, top), and
polyVBBIT/silica nanocomposites (b, bottom).
139 
 

The working temperature for an outdoor installed DSSCs can be as high as
60 °C. For this reason, the desired polyVBBIT/silica nanocomposites used as
electrolytes in solid state DSSC should have glass transition temperature (Tg)
lower than 60 °C. The Tg of polyVBBIT homopolymer and polyVBBIT/silica
nanocomposites was studied by Differential Scanning Calorimetry (DSC), shown
in Figure 4.7. PolyVBBIT homopolymer had a Tg of 84 °C, while polyVBBIT/silica
nanocomposites had a Tg of 95 °C. The reason for Tg increase from the free
homopolymer to the surface tethered polymer is easy to understand. In surface
tethered polymers, the mobility of polymer chains was more constrained
compared to that of free polymer, and more energy would be needed to pass
20,21

through the glassy state to the rubbery state, resulting to higher Tg.

To

-

obtain lower Tg, the BF4 anion in polyVBBIT could be replaced by a larger anion,
-

such as TFSI . Besides, other monomers with more flexible structure could be
synthesized and polymerized to replace VBBIT monomer. These work will be
done in future.

140 
 

Figure 4.7. DSC curves of polyVBBIT homopolymer and polyVBBIT/silica
nanocomposites.

Application as novel quasi-solid state electrolyte in DSSCs
Since polyVBBIT/silica nanocomposite is a white powder at room temperature, it
is difficult to use directly as electrolyte in DSSC. As shown in Scheme 4.3, we
22,23

mixed it with PMII, a commonly used IL in DSSCs.

The ionic conductivity of

polyVBBIT/silica nanocomposites and PMII mixture was measured, as shown in
Figure 4.8. Pure PMII showed the highest conductivity in all five samples, which
was 1.1 mS/cm at room temperature and 34.6 mS/cm at 90 °C respectively. After
141 
 

adding polyVBBIT/silica nanocomposites, the conductivity decreased. The more
polyVBBIT/silica nanocomposites was added, the lower was the conductivity,
which was mainly attributed to the viscosity increase and free volume decrease
of PMII. However, the conductivity decrease was relatively small. As in the case
of PMII/polyVBBIT/silica nanocomposites (20 wt%), the conductivity was 0.8
mS/cm at room temperature and 14.7 mS/cm at 90 °C, still quite high. The
conductivities of PMII mixed with more than 20 wt% polyVBBIT/silica
nanocomposites was also studied. The results showed incontinuous conductivity
data, which may be caused by uneven dispersion of polyVBBIT/silica
nanocomposites at high concentration.

Scheme 4.3. Pictures of polyVBBIT/silica nanocomposites, PMII and their
mixture.
142 
 

Figure 4.8. Conductivity of pure PMII and PMII with different amount of
polyVBBIT/silica nanocomposites.

The PMII/polyVBBIT/silica nanocomposites mixture was gelated just after
conductivity measurement from 25 °C to 90 °C. In Scheme 4.4a, the gel formed
was opaque. While in Scheme 4.4b, the gel formed was not as good as in
Scheme 4.4a, which was transparent. The concentration of polyVBBIT/silica
nanocomposites was critical in gel formation. PMII with lower concentration of
polyVBBIT/silica nanocomposites cannot form a gel after heating. To study the

143 
 

mechanism for gel formation, six different samples were made, including PMII
with bare silica nanoparticle, PMII with polyVBBIT homopolymer, PMII with
polyVBBIT/silica nanocomposites and another less viscous IL, 1-butyl-3methylimidazolium hexafluorophosphate (BMIHP), with bare silica, BMIHP with
polyVBBIT homopolymer, and BMIHP with the concentration polyVBBIT/silica
nanocomposites. All additives to IL were set to be 20 wt%. The results showed
that only ILs (PMII and BMIHP) with polyVBBIT/silica nanocomposites were
gelated after heating at 60 °C for 3 h, which indicated that both the silica
nanopaticle core and the polyVBBIT on its surface played a role in the gel
formation. The silica nanoparticle core worked as immobilized node while the
surface-anchored polymer chains entangled with each other after heating to form
a 3-D network in the system, resulting to gel formation.

a

b 

Scheme 4.4. Gels formed after conductivity measurement from 25 °C to 90 °C.
PMII with 20 wt% polyVBBIT/silica nanocomposites (a) and PMII with 15 wt%
polyVBBIT/silica nanocomposites. (b)

144 
 

Application in DSSC
The PMII/polyVBBIT/silica namocomposites gel electrolyte has been used in
DSSC. Three cells were fabricated and the cell performances were tested, as
shown in Figure 4.9 and Table 4.1. The photoelectric conversion efficiency was
calculated, as shown in Equation 1:

J  V  ff
Efficiency  sc oc
100%                    (1)
P
where Jsc is the short circuit current density, Voc is the open circuit voltage, ff is
2

the fill factor, and P is the power density of the light source (0.1 A/cm ). Cell 2
showed the best performance, which had a photoelectric conversion efficiency of
0.37 %. However, this conversion efficiency was quite low compared to the 7 %
conversion efficiency obtained in some similar studies.

14

There were a couple of

reasons for this poor performance. The first was the fabrication skills. As a newcomer in this area, we could only achieve a 1/5 conversion efficiency in repeating
the literature method. The second was that we did not tune the iodine
concentration in electrolyte. The iodine concentration played an important role in
the performance of DSSCs. Gerald Meyer and co-workers' study revealed that by
finely tuning the iodine concentration, the cell performance could be improved by
more than 100 %.

24

The third was that we did not add any additives to the gel

electrolyte. Additives such as 4-tert-butylpyridine and N-methylbenzimdazole

145 
 

could greatly elevate the open circuit voltage by shifting the conduction band
edge of TiO2 and preventing recombination reactions with triiodides.

25

Figure 4.9. J-V curve of the DSSC with PMII/polyVBBIT/silica nanocomposites
gel electrolyte

146 
 

Table 4.1. Short circuit current density (Jsc), open circuit voltage (Voc), fill factor
(ff) and conversion efficiency of DSSCs with PMII/polyVBBIT/silica
nanocomposites gel electrolyte.

Cell number

Jsc

/

2

-3

10

Voc / V

ff

Conversion
efficiency / %

A/cm
1

1.87

-0.45

0.38

0.32

2

1.90

-0.38

0.52

0.37

3

1.86

-0.46

0.41

0.35

147 
 

Conclusion
A

novel

PIL

modified

silica

nanoparticle

nanocomposite1-(4-vinylbenzyl)-3-butylimidazolium

composite

(polyVBBIT/silica

tetrafluoroborate)

was

successfully synthesized by surface initiated ATRP. The polymerization was
confirmed to be a first order reaction by kinetic study. FT-IR and TGA confirmed
a high density of polyVBBIT was grown on the surface of silica nanoparticle.
When finely dispersed in PMII and heated, a gel was formed. The gel electrolyte
was used as a quasi-solid state electrolyte in DSSC and a 0.37 % conversion
efficiency was achieved. The conversion efficiency was quite low compared to
the results reported by other researchers. However, by improving the cell
fabrication skills, finely tuning the iodine concentration in the electrolyte and
adding additives, a higher conversion efficiency can be expected and will be
done in future.

148 
 

Experimental Section
Materials
4-Vinylbenzyl chloride, 1-butylimidazole, sodium tetrafluoroborate, 2,6-di-tertbutyl-4-methylphenol (DBMP), CuBr (99.999 %), cetyltrimethylammonium
bromide, 2,2’-dipyridyl (bpy, 99+%), 2-propanol (anhydrous 99.5%), N,N,N',N',N"pentamethyl

diethylenetriamine

(PMDETA)

and

1,1,4,7,10,10-

hexamethyltriethylenetetramine (HMTETA) were used as received from SigmaAldrich except for bpy, which was sublimed before use. Silver nitrate was
purchased from Spectrum. Butyronitrile was purchased from Matheson Coleman
& Bell. Snowtex-XS colloidal silica, as an aqueous dispersion in pH 9-10 water,
was a gift from Nissan Chemical Industries. TEC-15 FTO glass was purchased
from Hartford Glass Co. TiO2 paste (DSL 18NR-T) was purchased from Dyesol.
N3 dye was given to us by the Nate Lewis group. Iodine 99.5% and hydrogen
hexachloroplatinate (IV) hydrate 40 % Pt were purchased from Acros. All other
chemicals and solvents were ACS reagent grade and used as received from
commercial suppliers without any further purification unless otherwise mentioned.
Synthesis of 1-(4-vinylbenzyl)-3-butylimidazolium tetrafluoroborate (VBBIT)
1-Butylimidazole (6.2 g, 50 mmol) was dissolved in 40 mL of CHCl3 in a dry flask,
followed by addition of 4-vinylbenzyl chloride (8.4 g, 55 mmol ) and an
polymerization inhibitor, 2,6-di-tert-butyl-4-methylphenol (0.055 g, 0.25 mmol).
The solution was stirred under N2 at 50 °C for 8 h. After that the solvent was
149 
 

removed by rotary evaporation. The resulting viscous liquid was washed with 25
mL diethyl ether three times and then dried under vacuum overnight at room
temperature. Yield: 12.4 g, 85 %. VBBICl (11 g, 40 mmol) and 2,6-di-tert-butyl-4methylphenol (0.044 g, 0.2 mmol) were dissolved in dry acetone (60 mL) in a dry
flask, followed by slow addition of sodium tetrafluoroborate (5.2 g, 48 mmol). The
reaction mixture was stirred for 3 days at room temperature and then filtered.
After the acetone was evaporated under reduced pressure, the unreacted
VBBICl and the inhibitor were removed from the waxy residue by washing with
distilled water and then diethyl ether until no AgCl precipitate was observed when
1

6

tested by silver nitrate. Yield: 11.8 g, 90 %. H NMR (d -DMSO, 300 MHz) δ 9.24
(s, 1H), 7.80 (d, J = 1.6 Hz, 2H), 7.51 (d, J = 8.3 Hz, 2H), 7.38 (d, J = 8.3 Hz, 2H),
6.73 (dd, J = 17.7, 11 Hz, 1H), 5.89 (dd, J = 11, 0.9 Hz, 1H), 5.40 (s, 2H), 5.30
(dd, J = 17.7, 0.9 Hz, 1H), 4.16 (t, J = 7.2 Hz, 2H), 1.82 - 1.71 (m, 2H), 1.31 1.17 (m, 2H), 0.88 (t, J = 7.3 Hz, 3H).
Synthesis of ATRP initiator modified silica nanoparticles.
The initiator precursor was synthesized according to a literature procedure. ωUndecylenyl alcohol (1.703 g, 10 mmol) and pyridine (0.84 mL, 11 mmol) were
dissolved in 10 mL of dry THF, followed by dropwise addition of 2bromoisobutyryl bromide (1.24 mL, 10 mmol). The reaction mixture was stirred at
room temperature overnight and then diluted by 20 mL hexane, washed with 3N
HCl (3 times, 10 mL each) and distilled water (3 times, 10 mL each). The organic
phase obtained was dried over sodium sulfate and filtered. Afterwards, hexane

150 
 

was removed by a rotavap and the oil-like product 10-undecen-1-yl 2-bromo-2methylpropionate was purified with a column (hexane/ethyl acetate 25:1 v/v). The
1

yield was 2.81 g, 88 %. Rf (hexane/ethyl acetate 10:1 v/v): 0.70. H NMR (CDCl3,
300 MHz) δ 5.85 - 5.72 (m, 1H), 5.02 - 4.86 (m, 2H), 4.15 (t, J = 6.6 Hz, 2H), 2.06
- 1.97 (m, 2H), 1.92 (s, 6H), 1.70 -1.60 (m, 2H),1.41-1.22 (br, 12H).
10-Undecen-1-yl

2-bromo-2-methylpropionate

(1.35

g,

4.23

mmol)

and

trichlorosilane (5 mL, 50.7 mmol) was charged to a dry flask, followed by addition
of Karstedt’s catalyst (10 µL). The reaction mixture was stirred at room
temperature overnight and then passed through a pipet column. Excess
trichlorosilane was removed under reduced pressure at 30 °C to provide (11-(2bromo-2-methyl)propionyloxy)undecyltrichlorosilane as an oil. Yield: 1.44 g, 75 %.
1

H NMR (CDCl3, 300 MHz) δ 4.16 (t, J = 6.6 Hz, 2H), 1.92 (s, 6H), 1.75-1.46 (m,

4H), 1.40-1.20 (br, 16H).
(11-(2-Bromo-2-methyl)propionyloxy)undecyltrichlorosilane (1.00 g, 2.20 mmol)
was dissolved in 100 mL dry toluene, and then added to a well-dispersed mixture
of silica nanoparticles in toluene (1.00 g silica, 100 mL dry toluene). The reaction
mixture was heated to 65 °C and stirred under nitrogen overnight. The product
was collected by centrifugation and washed three imes with acetone to remove
adsorbed (11-(2-bromo-2-methyl)propionylxoy)undecyltrichlorosilane. Yield: 1.7 g,
85 %.

151 
 

Synthesis of polyVBBIT/silica nanocomposites.
In a dry Schlenk flask, VBBIT (656 mg, 2.0 mmol), the surface initiator (148 mg,
-5

~2 x 10

mol) and PMDETA (20.8 mg, 1.2 x 10

-4

mol) were dissolved in

molecular sieve dried butyronitrile (2 mL). After 3 freeze pump thaw cycles, CuBr
-5

(5.7 mg, 4 x 10

mol) was charged into the Schlenk flask under nitrogen. The

reaction was run in nitrogen atmosphere at 90 °C with magnetic stirring. After 16
h, the reaction was stopped. The product was collected by centrifugation and
washed 3 times with acetone and DMF to remove residual reactants and
adsorbed homopolymer. The product was dried under vacuum (8 mTorr) at 60 °C.
Yield: 0.71 g, 88 %.
Characterization
1

H NMR analyses were performed on a Varian 500 MHz spectrometer with the

residual solvent proton signals as chemical shift standards. FT-IR spectra were
acquired from a Nicolet IR/42 spectrometer purged with dry nitrogen, signal
-1

averaging 128 scans at 4 cm

resolution. All IR samples were dried under

vacuum, grounded and mixed with dry KBr, and then pressed into pellets. TGA
was carried out in air on Perkin-Elmer TGA 7 instruments at a heating rate of
10 °C/min. TGA samples were first dried under vacuum overnight at 80 °C prior
to test. Samples were held at 120 °C in the TGA apparatus for 30 min to remove
all the physically adsorbed water before the heating process proceeded. DSC
was carried out on TA instruments DSC Q100 at a heating rate of 10 °C/min. The
152 
 

ionic conductivities of the Si-PVBBIT, PMII electrolytes were measured with an
AC impedance analyzer HP 4192A over the frequency range from 5 Hz to 13
MHz. Electrolytes were placed between a home-made cell. Conductivities of
different temperatures from 298 K to 363 K were measured. From the Nyquist
plot, the resistance of the electrolyte was estimated, and then the conductivity of
the electrolyte was calculated using the distance between two electrodes and
cross-section area of the cell. The cell performance was measured by
potentiostat 650D CH Instrument, and a Xe arc lamp (Horiba Jobin Yvon)
equipped with an AM 1.5 global filter set (Solar Light Co.) was used for solar
simulation.
Calculation of initiator content on the surface of silica nanoparticle
The content of initiator on the surface of silica nanoparticle can be roughly
calculated according to TGA data. As shown in Figure 4.3, the surface initiator
have a 4 % more weight loss compared to the bare silica nanoparticle. By
ignoring the displacement reaction of initiator to CTAB salts on the surface of
nanoparticle, and assuming the initiator has a complete decomposition and 0 %
weight retention at 850 °C, the initiator content can be calculated as follows:
assuming the content of initiator on the surface is X %, then the content of silica
nanopaticle is ( 100-X ) %. The total weight of initiator anchored silica
nanoparticle is 1 g. Silica nanoparticles loses 14 % of weight at 850 °C. Free
initiator loses 100 % of weight at 850 °C, and surface initiator loses 18 % of
weight at 850 °C.

153 
 

( 1g ) x ( 100 -14 ) % x ( 100-X ) % + ( 1 g ) x ( 0% ) x ( X ) % = 1 g x ( 100 - 18) %
X = 4.7
The initiator content on the surface of silica nanoparticle is 4.7 % of the total
weight of surface initiator.
Kinetic Study.
The polymerization condition was kept the same as mentioned above, except
that 4,4-dichlorobiphenyl sulfone (0.100 g) was added as an internal standard. At
certain time intervals, a syringe was used to sample reaction mixture (0.1 mL)
and diluted with acetone (3 mL) association with quick shaking to stop the
reaction. These samples were kept undisturbed overnight to allow the particles to
settle. The clear upper layer was drawn with a pipet and the solvent was
6

removed by rotary evaporation. The residue was dissolved in d -DMSO,
analyzed by

1

H NMR. The consumption of monomer was calculated by

comparing the integrals of specific peaks from the standard and monomer.
DSSC fabrication.
The DSSC was fabricated and tested by Lisa Harlow in Prof. McCusker's group.
The photoanode was prepared as follows: TiO2 paste was doctor-bladed onto
the FTO glass using a scotch tape mask with an area of 1 cm x 1 cm. It was then
baked at 375 °C for 10 mins, 450 °C for 5 mins, 500 °C for 10 mins, 550 °C for 5
mins. Once cooled to 90 °C they were immersed into a 0.3 mM N3 dye ethanol

154 
 

solution for 24 hours. For the cathode: thermalized platinum was used. 5 mM
hydrogen hexachloroplatinate (IV) hydrate in anhydrous isopropanol was drop
casted onto the FTO glass with two pre-drilled holes for electrolyte insertion.
They were let dry for 5 minutes on a flat surface then baked at 350 °C for 15
mins. The DSSC was fabricated as follows: PolyVBBIT/silica nanocomposties
were suspended in 0.6 g PMII (2.38 mmol), with the addition of 0.0604g I2
-4

(2.38x10

mol). The mixture was stirred for a half hour and then one drop was

placed onto the dyed photoanode. The electrolyte was spread over the film using
a glass pipet, and no pressure was applied. The electrolyte was pulled around.
The films were then baked at 90 °C for 1 hour. Surlyn was used as a spacer and
the electrodes were clamped together using binder clips and copper wires were
attached with silver conductive epoxy. The cells were tested after the epoxy set 4
hours later.

155 
 

REFERENCES

156 
 

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(2)
Wei, D.; Andrew, P.; Ryhanen, T.: Electrochemical photovoltaic cells review of recent developments. J Chem Technol Biotechnol 2010, 85, 1547-1552.

(3)
Yella, A.; Lee, H. W.; Tsao, H. N.; Yi, C. Y.; Chandiran, A. K.; Nazeeruddin,
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(4)
Gorlov, M.; Kloo, L.: Ionic liquid electrolytes for dye-sensitized solar cells.
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Zakeeruddin, S. M.; Gratzel, M.: Solvent-free ionic liquid electrolytes for
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Le Bideau, J.; Viau, L.; Vioux, A.: Ionogels, ionic liquid based hybrid
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Yoshida, M.: Ionic gelators: Oligomeric and polymeric electrolytes as novel
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Kubo, W.; Kitamura, T.; Hanabusa, K.; Wada, Y.; Yanagida, S.: Quasisolid-state dye-sensitized solar cells using room temperature molten salts and a
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Voss, B. A.; Bara, J. E.; Gin, D. L.; Noble, R. D.: Physically gelled ionic
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(11) Lu, J.; Yan, F.; Texter, J.: Advanced applications of ionic liquids in polymer
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(13) Fukushima, T.; Aida, T.: Ionic liquids for soft functional materials with
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160 
 

APPENDIX

161 
 

Ionic conductivity measurement - AC impedance spectroscopy
Ohms law (Equation 1) describes the current, I as a function of the applied
voltage, V and the resistance, R of an electrolyte.

R = V/I

(1)

Conductivity, σ, is defined as the reciprocal of resistivity, ρ. (Equation 2)

σ = 1/ρ

(2)

ρ = R(A/l)

(3)

and

where A is the area and l is the length of the electrolyte sample. It follows then
that

σ = l/RA

(4)

Resistivity and therefore conductivity is measured best by AC impedance
spectroscopy. An alternating voltage signal is applied to an electrolyte containing
cell, and the resulting current measured. This current is inversely proportional to
the impedance, Z, of the cell, and is frequency dependent. The electrochemical
response of the cell under measurement is rationalized in terms of an equivalent
circuit (Scheme A1), where C1 is the capacitance between the two electrodes, R1
162 
 

is the resistance of the electrolyte, C2 and R2 is the capacitance and resistance
between electrode and electrolyte respectively. The capacatance is calculated by
Equation (5), where εr is dielectric constant, ε0 is the permittivity of free space, A
is the area of the two electrodes and d is the distance.
C = εrε0A/d

(5)

Since d1 (the distance between the two electrodes ) >> d2 (the distance between
the electrode and the double layer), C1 << C2. The impedance of a capacitor, XC,
is calulated by Equation 6, where ω is the angular frequency and C is the
capacitance. Since C1 << C2, XC1 >> XC2.

XC = -1/ωC

(6)

Scheme A1: Equivalent circuit of the electrochemical response of the cell used in
conductivity measurement.
At ω = 0, both XC1 and XC2 approach ∞, the total impedance, Ztot = R1 + 2R2.
As ω increases, XC2 gets smaller and smaller, and approaches 0. While XC1 is

163 
 

still very large, Ztot = R1. When ω approaches ∞, both XC1 and XC2 approach 0,
Ztot = 0.
So ideally, the Nyquist plot of the above mentioned circuit should show like
Figure A1.

Figure A1. Ideal Nyquist plot of Scheme A1.

However, we cannot measure the impedance at frequency approaching 0 and ∞,
so we do not have the full right semicircle and the left semicircle does not end at
0. Figure A2 shows the Nyquist plot of a real sample. R1 is determined by the
point who has Z'' closest to 0.

164 
 

Figure A2: Example of a typical Nyquist plot obtained from AC impedance
measurement. (Sample is polyGBIMTFSI-co-polyME3MO-1/1 at 90 oC.)
 

165