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THE DEPENDENCE OF PHASE EQUILIBRIA ON THE CONFIGURATION

OF POLY(BUTENE—l)

By

John P. MullooLy

AN ABSTRACT

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
Department of Chemistry

1961

Approved

 

ABSTRACT

THE DEPENDENCE OF‘PHASE EQUILIBRIA ON THE CONFIGURATION

OF POLYCBUTENE- 1)
by John P. Mullooly

Phase equilibrium studies were made with isotactic and atactic
poly(butene-l) to determine the effect of configuration on the thermo-
dynamic interaction parameters as defined by the Flory-Huggins theory
for liquid-liquid phase equilibrium.

The whole atactic polymer was fractionated by a column elution
method. Molecular weights of atactic and isotactic fractions of poly-
(butene-l) were determined from intrinsic viscosity measurement. The
polymeric stereoisomers were characterized in the solid state by X—ray
and infrared spectroscopy, and melting point determination.

Precipitation temperatures were obtained for isotactic poly-
(butene-l) in a number of poor solvents, and two solvents where chosen
for liquid-liquid phase equilibrium studies. Phase diagrams were con—
structed for four atactic and three isotactic fractions. Precipitation
temperatures were observed visually.

The interaction parameters were found to differ for the two
stereoisomers of poly(butene-l). For example, for isotactic poly(bu-
tene-l) in diethyl carbitol, ‘1’ = 0.9hl and e = 371.7%; for atactic
poly(butene-l), they are O.h58 and 386.70A, reSpectiveLy.

In both systems studied a unique point was found where the
Flory—Huggins interaction parameter is equivalent for isotactic and

atactic poly(butene-l).

THE DEPENDENCE OF PHASE EQUILIBRIA ON THE CONFIGURATION

OF POLY(BUTENE—l)

By

John P. Mullooly

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Department of Chemistry

1961

ACKNOWLEDGMENT

The writer wishes to express his appreciation
to Dr. J. B. Kinsinger for his assistance throughout

the course of this work.

ii

II.

III.

IV.

TABLE OF CONTENTS

IN mo DUC’II ON 0 O O O O 0 O 0 O O O 0

Statement of Purpose . . . . . . .

me cry I O O O O O O O O O O O 0
Historical . . . . . . . . . . .

EXPERIMENTAL PROCEDURE . . . . . . .

Extraction . . . . . . . . . . . .

Fractionation . . . . . . . . .

Characterization of Isotactic Fractions

Crystalline State . . . . . . .
Viscosity Measurements . . . . .
Phase StUdieS O I O O O O O O O 0

DATA AND RESULTS . . . . . . . . . .
Extraction . . . . . . . . . .
Fractionation . . . . . . . . .
Infrared Spectra, Melting Points,

Patterns, Photomicrographs . .

Viscosity Measurements . . . . .
Phase Diagrams . . . . . . . . .

DISCIBSI ON 0 O O O O O O O 0 O O O O

REFWWCS O O O O O O O O O O O O 0

iii

Diffraction

PAGE

11

ll
11

13
13
15
17

17
17

18
21
28

b6
)48

LIST OF TABLES
TABLE PAGE

I. Thermodynamic Interaction Parameters for Polypropylene
in Phenyl Ether . . . . . . . . . . . . . . . . . . 10

II. Thermodynamic Interaction Parameters for Poly(butene—l)
in AniSOle . . . . C . C . . O . C O . C . . C . C . 10

III. Data for Fractionation A of Atactic Poly(butene-l) . . 17
IV. Data for Fractionation A' of Atactic Poly(butene-l) . . 17

V. Melting Point Data for Isotactic Fractions of
P01y(butene-l) O C O O O O C O O O O O O O O O O O O 18

VI. Intrinsic Viscosities and Molecular Weights for Fractions
of Isotactic and Atactic Poly(butene-l) . . . . . . 28

VII. Precipitation Temperatures of Approximately 1% Mixtures
of Isotactic Poly(butene—l) in Different Solvents. . 29

VIII. Phase Diagram Data for the System.Atactic Poly(butene-l)-
Dietlvl @rbitOl . C C O C . O . C C O . O 0 O O O O 30

IX. Phase Diagram Data for the System Isotactic
POIY<but€n€-l) - DietI-lyl CarbItOl o o o o o o o o o 31

X. Phase Diagram Data for the System.Atactic
P01y(but€n€-l) - Butyl CGIIOSOIVB o o o o o o o o o 32

XI. Phase Diagram Data for the System Isotactic
Poly(butene-l) - Butyl Cellosolve . . . . . . . . . 33

XII. Critical Data for Atactic and Isotactic Poly(butene-l)
in Diethyl Carbitol . . . . . . . . . . . . . . . . ' 3h

XIII. Critical Data for Atactic and Isotactic Poly(butene-l)
in Butyl Cellosolve . . . . . . . . . . . . . . . . 35

XIV. The Thermodynamic Interaction Parameters for Isotactic

and Atactic Poly(butene-l) in Diethyl Carbitol and
But/Y]. 02110801ve . . O O . . . . O O . O O . O . O O b2

iv

LIST OF‘FIGURES

FIGURE

1.

2.

IO.

11.

12.

13.

1h.

15.

l6.

Infrared Spectrum of Isotactic Poly(butene-l) . . . . .
Infrared Spectrum of Atactic Poly(butene-l) . . . . . .

Photomicrographs of Isotactic Poly(butene—l) . . . . . .
(a) Fraction B-8
(b) Fraction 8-? (after initial annealing period)

X—Ray Powder Spectra (Cu, Ka) of Poly(butene—l) . . . .
(a) Atactic Poly(butene-l)
(b) Unextracted Isotactic Sample
(c) Isotactic Poly(butene— 1), Fraction B— 7
(d) Isotactic Poly(butene- 1), Fraction B- 8

X—Ray Powder Spectrum (Cu, Ka) of Isotactic Poly(butene- 1)

Fraction B-8 O C O O O O O O I O O O O O O O O O O

X-Ray Powder Spectrum.(Cu, Ka) of Isotactic Poly(butene-l)

FraCtIODB-7..o....o............

§£/b versus C(g/IOO ml) for Four Fractions of Atactic
POIY<but€n€-l) o o a o o o o o o o o o o o o o o o o

gi/b versus C(g/IOO ml) for Three Fractions of
pIsotactic Poly(butene—l) . . . . . . . . . . . . . .

Phase Diagrams for Atactic Poly(butene—l) - Diethyl
carbitOI . C . O O O C C C C 0 O O O O O O O O O O 0

Phase Diagrams for Isotactic Poly(butene—1)-
Diethyl Carbitol . . . . . . . . . . . . . . . . . .

Phase Diagrams for Atactic Poly(butene-l) —
Butyl Cellosolve . . . . . . . . . . . . . . . . . .

Phase Diagrams for Isotactic Poly(butene-l) -
Butyl cellOSOIVQ . . O . . . C . . . . . O . O . O .

The Dependence of T on X for the System, Poly(butene- l)-
DiethlearbitoI.

The Dependence of TC on X for the System,
Poly(butene-l) - Butyl Cellosolve . . . . . . . . .

The Dependence of the Flory-Huggins Interaction Parameter
for the System, Poly(butene-l) - Diethyl Carbitol. .

The Dependence of the Flory-Huggins Interaction Parameter
for the System, Poly(butene-l) - Butyl Cellosolve. .

V

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I. INTRODUCTION
Statement of Purpose

The primary purpose of this investigation was to observe any
differences in the thermodynamic interaction parameters of the two
stereoisomers of poly(butene-l). Secondarily this work serves as a
partial step in the complete characterization of these polymers.

The theta temperature (9) and the thermodynamic interaction
parameter (X) are characteristic of a given polymer solvent pair. 9
is defined as the critical miscibility temperature for polymer of in-
finite molecular weight and may be evaluated by measuring critical
miscibility temperatures for a series of polymer fractions and extra-
polating to infinite molecular weight. The Flory—Huggins interaction
constant is a dimensionless quantity such that XkT measures the differ-
ence in energy of a solvent molecule immersed in polymer compared with
one immersed in pure solvent. (k is the Boltzmann constant and T the
absolute temperature). At the 9 temperature the polymer molecule be-
haves in an ideal manner and suffers no net interactions.

These parameters enter into many of the thermodynamic equations
defining properties of the polymer molecule. For example, according

to the simple 1attk2:theony, the reduced osmotic pressure is given by

%.= %%.+ constant (% — x)c + higher terms in c (1)

(w is the osmotic pressure, c the concentration, R the gas constant,

and M the molecular weight of the polymer,) so that to obtain the molec-
ular weight one must extrapolate measured values of n/c to infinite
dilution. This type of extrapolation is one of the more serious problems

1

2
encountered in polymer characterization. The better the solvent, the
lower the value of X and so the steeper the slope of fi/b versus c. At
the 6 temperature X is almost exactly 0.5, so that n/t = RT/M. 'van't Hbff's
law is then obeyed and no extrapolation is needed. Similar remarks ap-
ply to light scattering measurements. In theory then,a considerable
simplification is introduced by using a theta solvent for molecular
weight determinations.

According to hydrodynamic theory the polymer chains maintain a
minimal size under these conditions. The intrinsic Viscosity [fl ] when
measured at the 9 temperature is related to the unperturbed chain dimen-
sions( 5% is the unperturbed root mean square end to end dimension) by

the simple expression
[T1 16 = KMl/Z (2)

where K = constant (EEVM)3/E. Since this relationship is well establish—
ed, it is possible to calculate the average dimensions of the chain from
the intrinsic viscosity at 9.

Because interactions between segments of a polymer chain, in solu-
tion, are strongest when phase separation takes place, any difference in
the properties of a polymer, due to configuration, would be maximized
at this point. Therefore phase equilibrium studies may represent a
sensitive method for elucidating the differences in solution properties
of stereoisomeric polymers.

Liquid-liquid phase equilibrium.was chosen to study the solution
properties of isotactic (all g or all I) and atactic (random d and.ll

poly(butene-l).

3

Theoryl: 2: 3

The coexistence curves of two liquid phases can be calculated
if an analytical eXpression for the free energy of mixing is available.
The binary system studied here consists of a solvent and a polymer
characterized by the ratio of the molar volumes of polymer and solvent
(denoted by x). When polymer and solvent molecules are mixed there is
a non-vanishing heat of mixing due to the interaction of unlike Species.

In the Flory-Huggins original derivations it is assumed the en-
tropy of mixing in any polymer solution can be equated to the conforma-
tional entr0py of mixing. Any possible influence of the energies of
interaction on the entropy of mixing is neglected. Using volume frac-
tions, Vi’ the heat of mixing of a binary solution of n; moles of sol-

vent and n2 moles of'polymer is equated to

£51“ = xv1v2(n1 + ma) (3)

(v1 = volume fraction of solvent, v2 = volume fraction of polymer,)
in analogy to the van Laar-Hildebrand-Scatchard expression for molecules
of equal size. The changes of the partial molar heat content on mix-

ing as obtained from (3) are:

AH
and €¥2'= XxvlZ (5)

Assuming that the conformational entropy represents the total entropy

change on mixing the free energy of mixing is:

AFM = RT[nlln v1 + nzln v2 + X nlvz] (6)

The changes of chemical potential on mixing for the two components are

then:

h

Aul = RT[ln v1 + (l - %)V2 + XVQZJ (7)

Auz RT[ln v2 - (x - 1)vl +-Xxv12] (8)

x, as defined by (3), is known as the interaction constant and equation

(6) as the Flory-Huggins expression.

The conditions for equilibrium between two phases in a binary
system are expressed by stipulating equality of the chemical potentials
in the two phases; that is

#1 g H11 (9a)

H2 = #21 (9b)
where the prime denotes the more concentrated phase. Fulfillment of
(9a) requires there be two concentrations at which the chemical poten—
tial “1 has the same value. This requires that ”1 pass through a min-
imum and then a maximum as v2 is increased from zero to unity. Similar-
ly in order for (9b) to be satisfied #2 must exhibit a maximum and a
minimum. Since ”1 and ”2 are derived by differentiating the same free
energy expression (6) one must pass through a maximum where the other
is at its minimum. A point of inflection characterized by the condition

Of zero curvature

.J;.E1 . 0 (10)

must necessarily occur between the minimum and the maximum in the

curve. At both the minimum and maximum

07

1 1 =0 (11)
“V?- T,P

These two conditions then constitute the necessary and sufficient con-

dition for incomplete miscibility. If the curve representing “1 as a

5

function of Va decreases monotonically with v2, total miscibility is

assured. (As the interaction constant is increased, going to poorer
solvents, eventually a minimum and a maximum will appear; their appear-

ance signifies incomplete miscibility. Ordinarily a poor solvent for

a given polymer becomes poorer with lowering of temperature. A totally
miscible system at higher temperatures may be converted to one of lim-
ited miscibility by lowering the temperature. At some temperature, T ,

P
phase separation takes place. At Tb the previously monotonic curve

begins to exhibit a minimum, a maximum, and an inflection. These
features occur simultaneously at the same concentration.

Differentiating (7) for the chemical potential of the solvent

with reSpect to v1 and equating the result to zero, we obtain

1 fl]- : l — - l _ r- a
_RT' 6 V1 v1 (1 x) “V2 O (12)

and a second differentiation gives

 

s2
R% 0 AH]. - - L. + 2x, . O _ (13)
avlz V12

Denoting critical values with a subscript c, we obtain as the solution

of (12) and (13)

 

1 !
2C 1 4. Xl/z ( )

xC -% (1 + x-l/m <15)

For large values of x, VZC is very small and XC very little over 1/2.

Since X is a free energy parameter it can be written as the sum

6
of two terms, a temperature independent termxS and.a term‘x,H which

varies as l/T and is written fi/T. G, the Flory temperature, is defined

as the critical temperature of mixing of an infinitely long polymer,

and is given by

v;

where K is the heat of dilution parameter. I , the entropy parameter,

is defined as 1/2 - X“. For this hypothetical polymer (15) becomes
upon introduction of these defined quantities
\3 - 1/2 - x3 - {3/9 (16)
The Flory-Huggins interaction parameter becomes
W 6
x - 1/2 - i (l-'T) (17)

Equating equations (15) and (17), and rearranging terms, gives a linear
relationship between the critical temperature and x, from'which Y and

9 can be evaluated experimentally

l + 1 1 l
W + 18
TC 5'9 (x 1/2 2x) ( )

 

(DH—-

Quantitative agreement between experiment and (1h) is poor. There is

no freedom for any deviation from this relationship within the frame-
work of the Flory—Huggins free energy of mixing expression. Tompa has
therefore tried to improve the theory by making a mathematical extension.
X: at a given temperature, is assumed to depend linearly on v2. Math-
ematically this is equivalent to adding a cubic term to (7). Designat-

ing 5 x/'8v2 by k, the equations obtained for the critical point are

l l
1;: - (1 - E) - 2xv2 - kvz2 - O (19)

and

 

--1-+2X+)4kv2=0 (20)
V2

These equations determine, for a given solvent/polymer system, sets

of corresponding values of VZC andflic for each value of k. Using
numerical methods Tompa4 demonstrates that the influence of any con-

centration dependence of X is very much larger on Vac than on XC,

This then gives at least a formal description of the observation that

XC is often much better represented by the Flory-Huggins theory than

VZC 0

.At the theta temperature the net interaction between solvent

and polymer segments is zero. The polymer molecules are able to pene-

trate each other freely, and the excluded volume of the molecules is

also zero. At this temperature, the polymer molecules assume their

unperturbed dimensions, r02. The expansion factor, a, is defined by

r2 = 0. r02 (21)

['Jr2 is the root mean square end to end distance of the chain in a
perturbed state] and is a function of the thermodynamic interaction

parameters;
w e
a5 - as ‘ Cm ‘ (1 "T) Ml/é (22)

a approaches one as T approaches 9. Cm is a constant for a given

molecular weight and is calculated from the expression

cIn = (27/25/2 nS/Z)(VZ/Nv1)(F;5/M)‘3/Z (23)

(V is the Specific volume of the polymer, V1 the molar volume of the

solvent, and.N Avogadro's number).

8

The interaction parameters are characteristic of the non-ideal
behavior of polymer solutions, but their exact significance has not
been determined, theoretically. Flory assumes that the same parameters

describe both inter- and intra-molecular interactions, although this

has been questioned5. The dilute solution theory gives different values

.Tl

forL . In dilution solutions, the simple lattice theory predicts

that (‘3 - 1/2)’3 1/2 for intermolecular interactions where Z, as de-
fined, represents the lattice coordination number. Much more compli-
cated expressions for the interaction parameters have been derived by
other methods.°’7’5 These methods consider preferential interactions,
molecular size and shape, and chain stiffness.

The effect of stereoregularity has not been directly considered.
Therefore, changes in the interaction parameters due to configuration

must be postulated by indirect methods. This can be done by making

qualitative predictions about the effect of stereoregularity on the

quantities which determine the values of the interaction parameters.

Historical

The most thorough investigations of the phase relationships of
solvent/polymer systems are those carried out by Schultz and Flory9’10’11

These workers studied atactic polystyrene in various solvents. In
particular, precipitation temperatures of four well—fractionated

samples of polystyrene in solutions of cyclohexane were determined.

The experimental binodals agree qualitatively with respect to the shape
of the curves with the Flory-Huggins theory. The quantitative agree—
ment is poor; the critical concentrations are higher than those predicted

by theory. Similar results were obtained with the cyclohexanol/

9
polystyrene and diisobutylketone/polyisobutene systems.

The polyethylene system as investigated by Richards12 exhibited

a region of liquid—liquid phase separation in the dilute range, with

the critical point occuring at a very low polymer concentration.

Liquid-crystalline phase separation occurred at higher concentrations;

this region extended from a triple point, where three phases are
present in equilibrium, to the melting point of pure polyethylene. The
size of the liquid—liquid region decreased in better solvents; only
liquid—crystalline separation was observed in the best solvent used.

A few papers have appeared recently which have shown that poly-
mer stereoisomers retain their individuality in solution. Light scat-
tering measurements have been made by Kinsinger on the polypropylene
system.13 Small differences in the second virial coefficients of iso-
tactic and atactic polypropylene were observed. In osmotic pressure
measurements on isotactic and atactic polystyrene, Danusso and Moraglio
found definite differences in the second virial coefficients.14

The first study of the phase relationships of polymeric stereo-

isomers was reported by Kinsinger and.wesslhmpis Phase diagrams of

carefully characterized fractions of atactic and isotactic polypropyl-
ene were determined and binodals characteristic of liquid-liquid separ-
ations for both stereoisomers were obtained in phenyl ether at temper-
atures near the melting point of the isotactic polymer. Reciprocals

of the critical temperatures determined from the phase diagrams were
plotted versus (l/xl/2 + l/2x) and the parameters 'Y and a were evalu-
ated. Curves for atactic and isotactic polypropylene were found to
differ considerably in both slqpe and intercept. The data reported

is summarized in Table I.

10

Table I. Thermodynamic Interaction Parameters for Polypropylene in
Phenyl Ether15

 

 

Isomer 9(?K) y

Isotactic ‘h18.h l.hlh

Atactic D26.5 0.986
Difference 8.1 O.h26

 

In a private communication Krigbaum reports differences in the
theta temperatures and entropy parameters for atactic and isotactic
poly(butene-l) in anisole. Critical miscibility temperature measure—

ments were used and the data reported are summarized in Table II.

Table II. Thermodynamic Interaction Parameters for Poly(butene-l) in
Anisole.16 '

 

 

 

Isomer 6(0K) Y
Isotactic 362.3 0.956
Atactic 359.h 0.7h0

Difference 2.9 0.216

 

II. EXPERIMENTAL PROCEDURE
Extraction

Samples of atactic and crystalline (isotactic) poly(butene—l)
were provided by the Petro—Tex Division of Food Machinery Corporation
of New Jersey. The atactic sample was clear, colorless and rubbery
while the isotactic polymer was a white, non-tacky fluffy powder. No
information was given by the supplier as to the method of preparation
used. It was indicated that the samples underwent a solvent treatment
subsequent to preparation; no details were given. Initial attempts to
obtain phase diagrams with fractions prepared from untreated samples
indicated an insoluble content, thought to be inorganic catalyst frag-
ments and suggested that the solvent treatment was incomplete. An
extraction method was therefore used, employing isooctane which has been
reported byNatta17 to act as a selective solvent for the atactic iso-
mer. Observation of the samples under a polarized microscope also
indicated the need to purify the samples before proceeding with the

phase studies.
Fractionation

The atactic polymer was fractionated using an elution sand col-
umn method.18 Butyl cellosolve served as the carrier, dyclohexane and
acetone were used as the solvent and non-solvent reSpectively. The
solvent and non—solvent were distilled before use; the observed boiling
points and refractive indices were 81°C., l.h29l and 57°C., 1.3583 re-
spectively. Xylene was refluxed through the outer jacket of the elution

ll

12
column while the butyl cellosolve solution was introduced into the
column. The heat was then turned off causing the polymer to precipi-
tate differentiallygaccording to molecular weight,on the sand particles.

Oxidative degradation of the polymer was prevented by the addi-

tion of a stabilizer to the butyl cellosolve solutions (2,6-di—t—butyl-
p—cresol).

The elution was carried out at room temperature employing a ten
ml. increment of solvent-nonsolvent with an elution rate of approxi-
mately twenty drops per minute. One hundred ml. portions of the exit

eluent were collected, heated to dryness on a steam bath, and the
fractions were dried to constant weight in vacuo at 80—90oc, In the

initial fractionation 2.8 g. of the extracted atactic sample was used
and yielded eight fractions. Fraction four accounted for more than
half the weight of the sample. Fractions three and four were returned

to the column and the fractionation procedure was repeated. This

second fractionation yielded five fractions. The fifth fraction of the
first fractionation (designated.A—5) and the fourth and fifth fractions
of the second fractionation (A'-b,.A'—5) were used for the subsequent
studies.

Viscosity measurements revealed that all the atactic fractions
of sufficient weight were of relatively low molecular weight. The ex-
traction step was suspect of causing degradation since it was carried
out at the boiling point of isooctane (11800.) and involved prolonged
exposure (2 days). To check this a l g. sample was extracted with
hexane at room temperature and the viscosity of the extract was deter-
mined. This extract was of comparable molecular weight. The atactic

fraction denoted c-2 was obtained by fractional precipitation and was

13
available from.previous work in this laboratory.

Three isotactic fractions (designated B-h, B-7 and B-8) were
obtained from C. C. Wilkins. They were prepared by a similar column

fractionation method, the details of which will be given in his thesis.
Characterization of Isotactic Poly(butene-l) in the Crystalline State

The melting behavior of the isotactic fractions was observed
using a Kgfler Hot Stage and a polarizing microscope. Samples were
prepared for observation by pressing between two microscope slides,
melting, quenching and annealing to develop large Spherulites. The
heating rate was about 0.50/min. near the melting point.

X—ray Spectra were taken using the powder camera and the auto-
matic recording diffractometer. Since the samples could not be ground

fine enough to be inserted into the X-ray capillary tube, a film of

polymer was cast on the exterior of the tube by dipping it into poly-

mer melt. Cu, Kc radiation.was used and the samples were exposed for
three hours. The diffractometer samples were prepared by melting the

polymer in the sample holder so that a fairly even surface was produced.
Infrared spectra of the stereoisomers were taken with the Perkin

Elmer Infrared Spectrophotometer, Model 21. Films were cast on salt

plates by placing a few drops of a concentrated cyclohexane solution

on the plate and then drying in a vacuum oven at 80-9000,

Viscosity Measurements

Intrinsic viscosity measurements were carried out for atactic

and isotactic poly(butene-l) in benzene at 30°C. and in n-nonane at

114
80°C. respectively. Pure Grade normal nonane was used as received
from Phillips 66 Hydrocarbons (99 mol % minimum)(b.p. l5l°C., nd20 l.h052),
Chemically pure benzene was distilled before use (b.p. 80°C., nd20 1.501h).
A Cannon—Ubbelohde Micro Dilution Type viscometer was used for both
polymers.

Special techniques were required for handling the crystalline
polymer at high temperature. The isotactic samples were weighed to
constant weight in 1 m1. volumetrics. Upon addition of the solvent
one to two hours of heating at from 80-900 were required to complete
the initial solution. The solution was then cooled to room temperature
and weighed. The polymer fractions dissolved rapidly in nonane when
heated a second time and the solutions were immediately filtered through

a heated glass frit into the viscometer immersed in the constant temp-

erature oil bath.

The polymer solutions were prepared so the relative viscosity

fell within the limits 1.2 to 1.9. Both Asp/t and lnTLel/b were cal—
culated and.plotted against the concentration according to the Huggins
viscosity relationships

J22 =H1+wmzc

C

lnnrel = [n J _ fi[q 12C

c
A double extrapolation to zero concentration was performed by least

squares to give the intrinsic viscosity, [A ].

The molecular weights were calculated by the empirical Mark-

Houwink equation

15
[T1]=KMa
For the atactic polymer in benzene at 30°C. Natta'slfialues of K =
2.15 x 10"4 and a = 0.685 were used. Krigbaum's16 values of K=0.585 x
10—4 and for a = 0.80 for isotactic poly(butene-l) in n-nonane at 80°C.

were used.
Phase Studies

Various solvents were investigated to determine their useful-
ness for liquid-liquid phase equilibrium studies. The following prop-
erties were required: the solvent must be sufficiently poor to give
liquid—liquid phase separation with isotactic poly(butene-l); it must
be inert and high—boiling. Solutions of approximately one percent iso-
tactic poly(butene-l) were prepared and the mode of phase separation
was determined. Where liquid-liquid.phase separation occurred the
precipitation temperatures were reproducible, but this was not the case
for liquid-crystalline separation. The endpoint for the latter type
of separation was not reproducible because of the dependence of the
precipitation on the rate of cooling. When liquid-crystalline phase
separation occurred the precipitate formed by cooling would not dissolve
until the temperature was raised from 5° to 20° above the endpoint;
cooling slightly below the temperature at which the precipitate dis-
solved would not induce another phase separation.

From this preliminary investigation two solvents were chosen for

the phase studies, diethyl carbitol and butyl cellosolve. These two

solvents were chosen since they satisfy the requirements given above
and differ considerably in solvent power. If differences in the thermo-

dynamic interaction parameters of the two stereoisomers were observed

16

it would be interesting to see whether this difference is dependent
solely on the degree of stereoregularity of the polymer or whether
there is a solvent effect.

The experimental method for the determination of the phase dia-
grams consisted of preparing solutions near precipitation and then
causing precipitation to take place by lowering the temperature. Poly-
mer samples, which varied from ten to twenty milligrams were weighed
into two ml. volumetric sample tubes. The solvent was weighed into
the tube from a syringe, and the tube sealed.

The solvents were used as received from Union Carbide. Boiling

points and refractive indices were determined (b.p. 188°C., n 20 = l.hllO

d
for diethyl carbitol and b.p. 173°C., nd2° = l.hl92 for butyl cello-
solve).

Precipitation temperatures were determined, visually, by the
following procedure: The bath temperature was lowered at the rate of
approximately 1° per minute until turbidity appeared in the solution;
the temperature was then raised until the sample cleared. This cycle
was repeated at a slower rate (about 0.20/min) to obtain the endpoint.
Oxidative degradation was prevented by adding a stabilizer to the butyl
cellosolve solution (2,6—di-t-butyl-pfcresol).

The Specific volumes of the polymers were calculated from dila-
tometric data reported by Natta.2° Density temperature relationships
for diethyl carbitol and butyl cellosolve were determined by making

density'measurements at several temperatures with a Gay-Lussac pycnometer

which had been calibrated using mercury.

III. DATA.AND RESULTS
Extraction

The bulk atactic sample was extracted with isooctane at its boil-
ing point (118°C.) for N8 hours. 0f the h.62 grams of atactic sample
used, 0.023 grams of insoluble material remained in the Soxhlet extraction

cup after this period.
Fractionation

Table III. Data for Fractionation A of Atactic Poly(butene-l)

 

 

Fraction A-l A-2 A-3 A—h A-5 A-6 A—7 A—8 Total Wt. of Sample

 

Wt. of 0.01 0.07 0.28 1.50 0.58 0.03 0.02 0.02 2.51 g. 2.80 g.
Fraction(g)
% 0f Sams

ple 0.h 2.5 10.0 53.6 20.7 1.1 0.7 0.7 89.6%

 

Table IV. Data for Fractionation A' of Atactic Polbeutene-l)

 

 

Fraction A'-l A'-2 A'-3 A'-h A'-5 Total Wt. of
Sample

Wt. of
Fracti0n(g) 0.10 0.2u 0.38 0.59 0.L0 1.71 g. 1.78 g.

% of Sample 5.6 13.5 21.3 33.1 22.5 96.2%

 

17

18
Infrared.Spectra, Melting Points, X-ray Diffraction
Patterns and Photomicrographs

The infrared Spectra of isotactic and atactic poly(butene-l) are
given in Figs. I and II reSpectively. These spectra compare well with
those reported by'Nattaglexcept for the 5.8hp.peak in the atactic sample
which might be indicative of unsaturation.

Samples for melting point determination were pressed between
microscope slides, melted, quenched and then annealed. .After annealing
at 80°C for h8 hours the samples were observed with a polarized micro-
scope. Some crystalline aggregates (Spherulites) were found to be
present. The samples were then melted and allowed to cool slowly on
the Kgfler Hot Stage. This treatment resulted in an increased number
of large Spherulites. The melting point was then determined and was
taken as the temperature at which the last trace of birefringence dis-

appeared.

Table V. Melting Point Data for Isotactic Fractions of Poly(butene—l)

 

 

 

Fraction Melting Range Disappearance of last Heating Rate
(0C.) trace of birefringence
B—h 121-125.5 125.5 0.50/h1n.
3—7 12h-128 128 0.5°/hino
B-8 126.5—130 130 0.50/m1n.

 

Fraction B-7 was unusual in its melting behavior. After the A8 hour
period of annealing the Spherulites morphology was different than the

other fractions. The Maltese' Crosses appeared to be imperfectly

formed. Upon initial melting the observed melting point was about

l9

 

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20

75 Transmi 35 i on

 

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81?

 

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in. m. H3389 mugged: ow b.8030 poQAucdofimuC

Geo

 

 

E.

21
105°C. Slow cooling resulted in growth of the aggregates but no morph-
ological change was noted. The melting point was again determined and
was found to be from 105 - 110°C. This sample was returned to the 80°C.
annealing oven and investigated.periodically. The observed melting
point increased with annealing time and only after about 100 hours was
a constant value obtained, at which time the crosses seemed well formed
and resembled fractions B-h and B-8. The metastable aggregates of
fraction B—7 are compared photographically with the stable form in
Fig. 3.

Slight differences will be noted in the X—ray Spectra of frac-
tions B-7 and B-8 as given in Fig. A. .All these spectra were taken
approximately one hour after crystallization from the melt. Marked dif—
ferences are noted when Geiger counter registration of the X-ray Spectra
is used (Figs. 5 and 6). These Spectra agree well with those given by
Natta.21

Natta21322reports crystal dimensions for two polymorphic Species
of isotactic poly(butene-l). The unstable species as reported consists
of four monomeric units per repeating unit with a repeating unit along
the fiber axis of 6.859A. The stable form consists of 3 monomeric
units per repeating unit with a 6.50°A repeating unit along the fiber
axis. Natta reported 126-128°C. as the melting point of the stable

form of isotactic poly(butene-l).
Viscosity Measurements

The viscosity data for the atactic and isotactic fractions are

plotted in Figures 7 and 8 respectively.

\3

r1

22

 

(a) Fraction B-8

 

(b) Fraction B-7 (after initial annealing period).

Fig. 3.

Photomicrographs of Isotactic Poly(butene—l).

23

 

(a) Atactic Poly(butene—l)

.10)

(b) Unextracted Isotactic Sample

-0-

(c) Isotactic Poly(butene—l) Fraction B-7

-0-

(d) Isotactic Poly(butene— 1) Fraction D— 8
Fig. A. XvRay Powder Spectra of Poly(butene—l)

   

 

 

211

v

 

 

1min!

 

g.-

a...

 

 

H
4--

Eu. m. x133. wanna. muonwg «on. E; 0H Hmonmofin
35.08255. 3838 ma.
a rogue mug». namgwfinugoa H3! .523

 

 

 

up

'—
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H
M
:1-

ma aw

 

.5

“W

we gonna.“

 

25

Intensity

 

 

 

 

 

 

who. a. xuwmw pecans mvaownca.aoce xev om Hmonwnwgo
wOHVAUcwosnqu wanedmos mud.
Am wanna manna onwmnmupmnm«»os mnos.snpwv

 

. P 11* P 1”].
5% fl 0: E. as B
no nounoou

-r-

HH

 

 

 

0.17

0.3

0.37i

0.39

0.33‘

 

Fig. 7. 7lap/c versus C(g/ICX) ml) for

four Fractions of Atactic Poly(butene-l).
Solvent was Benzene at 30°C.

0.27“

0.25‘

0.23d

0.211

 

0.19

 

 

0.17

 

1.11-

1.3"

2?

 

 

 

Fig. 8. "Sp/c versus c(g/100 ml) for Three
Fractions of Isotactic Poly(butene-l).
Solvent was n-nonane at 80°C.

 

1.2

'r i i 1L i 1L 1-
0.1 0.2 0.3 0.14 0.5 0.6 0.7
C(g/IOO ml)

 

28

Table VI. Intrinsic Viscosities and Molecular Weights for Fractions of
Isotactic and.Atactic Poly(butene-l)

 

 

 

Isomer Fraction [n ] M.W.*
Atactic A'-h 0.170 17,010
A'—5 0.221 2h,950
A —5 0.296 38,600
c —2 0.352 t9,210

Isotactic B—h 1.36u 287,800**
B—7 1.7811 1102.500
B-8 1.90t A36,700

 

*Calculated from Natta's relationship for atactic poly(butene-l) in
benzene at 30°C.

**Calcu1ated from Krigbaum's relationship for isotactic poly(butene-l)
imin-nonane at 80°C.

Phase Diagrams

Preliminary tests were made with approximately 1 percent mixtures
of unfractionated isotactic polymer. The modes of phase separation are
designated L - L for liquid - liquid separation and L - C for crystal-
lization.

Phase diagrams in the dilute range were obtained for both stereo-
isomers in diethyl carbitol and butyl cellosolve.

Weight fractions, obtained experimentally, were converted to
volume fractions by assuming negligible volume change on mixing; there-

fore

V2 = (Wzvgp)/(Wid1 +‘w2VSp)

where the values of the specific volume and density were taken at the

29

Table VII. Precipitation Temperatures of Approximately 1% Mixtures of
Isotactic Poly(butene-l) in Different Solvents.

 

 

ii-

 

Solvent 8: Tfi(°C) Phase Separation
Phenyl Ether 1&0 L - L
Butyl Cellosolve 8.9 150 L — L
Decyl Alcohol 80 L - C
Octanol 10.3 82 L - C
AniSOIe 85 L - L
Phenetole 50 L - L
Diethyl Carbitol 90 L - L
Cyclohexanone 9.7 95 L - C

 

*5 is a solubility parameter defined as the square root of the cohesive
energy density

5 - (CED) 1/2 = (Evan/WV?-

30

Table VIII. Phase Diagram Data for the System Atactic Poly(butene—l) -
Diethyl Carbitol

 

 

 

Fraction Volume fraction (v2) 339(0C°)
A'-h 0.131 h1.8
0.0752 A3.9
0.0508 L3.7
0.0389 h3.h
0.0285 h1.8
0.020h h0.h
A'-5 0.0998 53.5
0.0650 55.0
0.0516 55.h
0.0392 55.3
0.0309 55.2
0.02h0 53.5
A-5 0.120 56.5
0.0580 60.5
0.0382 60.h
0.0270 59.5
0 017h 57.5
‘c-2 0.130 70.0
0 0622 72.6
0.0359 72.7
0.0273 72.3
0.0197 71.3
0.0139 70.2
0.00950 68.

 

Table IX. Phase Diagram Data for the System Isotactic Poly(butene-l) -

Diethyl Carbitol

31

 

 

 

Fraction Volume fraction (v2) Tp(°C.)
B-h 0.0776 ‘90.h
0.0355 90.2
0.0206 90.3
0.01h3 89.6
090960 - 88.2
0.00800 87.7
B-7 0.0776 89.2
0.0373 90.5
0.021h 90.7
0.017h 90.6
0.0130 90.1
0.009600 89.5
B-8 0.0732 89.0
0.0377 90.7
0.0250 91.0
0.0191 91.0
0.0152 90.h
0.0119 90.2
0.0102 90.0
0.00890 88.9

 

32

Table X. Phase Diagram Data for the System.Atactic Poly(butene-l) -
Butyl Cellosolve

 

 

 

Fraction Volume fraction (v2) Tp(°C.)

A'-h 0.099h .95.1
0.0657 95.1

0.0507 95.0

0.0355 9h.0

0.0108 90.9

0.00990 89.6

A'-5 0.108 109.0
0.0831 110.2

0.0610 111.8

0.0h96 111.7

0.036h 111.5

0.0333 111.0

0.0255 110.5

0.0201 109.8

0.01t6 108.5

A-5 0.0822 117.5
0.0h65 118.8

0.0379 119.5

0.0300 119.5

0.025 119.0

0.0203 118.2

0.0157 117.6

0-2 0.0731 132.8
0.0h28 13h.5

0.0338 13h.5

0.0292 13h.0

0.022u 132.9

 

33

Table XI. Phase Diagram Data for the System Isotactic Poly(butene—l) —
Butyl Cellosolve

 

 

 

Fraction Volume fraction (v2) TP(°C.)
B-h 0.0329 1h3.6
0.0162 lh5.2

0.0107 1h5.h

0.00870 1h5.0

0.00h70 1A3.1

B-7 0.0t71 1h6.6
0.02b6 150.0

0.0158 l50.h

0.012h 150.6

0.00890 1h7.7

0.00660 _ 1116. 1

B—8 0.0163 150.9
0.0131 151.0

0.0102 151.1

0.00887 151.0

0.00680 150.8

0.00610 150.6

0.00h70 150.0

0.00372 1h8.5

 

3h
precipitation temperature. The precipitation temperatures were plotted
against volume fractions to obtain the phase diagrams. Critical points
were determined from rectilinear diameters.

Precipitation temperatures were reproducible to i0.3°C. and
were independent of the cooling rate. The endpoint varied with the view-
ing angle; all of the endpoints in this work were obtained by sighting
through the sample perpendicular to the light path.

The critical data for atactic and isotactic poly(butene—l) are

summarized in Tables XII and XIII.

Table XII. Critical Data for Atactic and Isotactic Poly(butene—l) in
Diethyl Carbitol

 

 

 

‘Isomer Fraction TC(°C) x v2C(exp) v2c(calc)*
Atactic .Ai-h hh.1 108.0 0.0675 0.0878
A'-5 55. 157.5 0.0517 0.0738
A-5 60.6 2h3.1 0.0510 0.0603
C-2 72.8 308.0 0.0h80 0.0539
Isotactic B—h 90.h 1815 0.0261 0.0229
B-7 90.8 2537 0.02h5 0.0195
B-8 19.1 2751 0.0235 0.0187

 

*Calculated from the Flory-Huggins expression

= l...—
1+x1/3

 

V20

An odd feature of the phase diagrams for poly(butene-l) in diethyl car-
bitol was the deviation of the critical volume fractions from ideality.
Whereas the deviations were negative for the atactic fractions they were

positive for the isotactic samples.

35

Table XIII. Critical Data for Atactic and Isotactic Poly(butene-l)
in Butyl Cellosolve

 

 

 

Isomer Fraction TC(°C) x; vzc(exp) v2C(calc)*
Atactic A LA 95 . 1 11.5 . 3 0.0590 0.0766
A'-5 111.8 211.0 0.0520 0.06hh
A— 119.5 32h.9 0.0350 0.0526
C—2 138.6 h09.9 0.0h10 0.0h7l
Isotactic B—h lh5.5 238A 0.0125 0.0201
B-7 150.6 3309 0.01h0 0.0171
B-8 151.1 3588 0.0110 0.016h

 

(*Calculated from the Flory-Huggins expression (see Table XII).

x” the ratio of the molar volumes of polymer and solvent is calculated

from

where V1 is the molar volume of the solvent. The values of the Specific
volume of the polymer and the molar volume of the solvent were taken
at the critical temperatures.

Figures 9 through 12 give the phase diagrams of the stereoiso-
mers in the solvents studied.

As predicted by theory, plots of l/TC versus [l/xl/2 + l/2x]
were linear within experimental error for both systems. Straight lines
were obtained by a least squares fit. Figures 13 and 1h give the de-
pendence of the critical temperature on the ratio of molar volumes, x,
for the diethyl carbitol and butyl cellosolve systems reSpectively.

In both solvents the slopes and intercepts are different for the
two stereoisomers; this results in a sizable difference in the thermo-

dynamic interaction parameters.

36

 

72..-

71..

69a)-

61:-

 

 

0200

0302

0. 0).

0106

Fig. 9. Phase Diagrams for Atactic Poly—
(butene-l)-Diethyl Carbitol --- rectilinear
diameter.

 

 

 

(108 of 10 0112 0.1111

V2

37

 

(I)
000‘?
l

91‘7

 

Fig. 10. Phase Diagrams for Isotactic Poly-
(butene-l)-Diethyl Carbitol --- rectilinear dia-
meters.

 

B-7

B-h

0.03 0101. 0.05 . 0!06 0.07 02

V2

 

T
mi

38

 

135

13h ‘
133 ~

109 ‘

9h 3

:93‘
92

A

89

A

1

1

 

C-2

0' A-S

 

 

Fig. 11. Phase Diagrams for Atactic Poly(butene-l)

 

- Butyl Cellosolve --- rectilinear diameters.
I 4 . I l l I n
I I l l T 1 ‘1
0.00 0.02 0.0h 0.06 0.08 0.10 0.12 0.1h

V 2

 

39

 

151 -

150 ‘

1A9 ‘

1&8 ‘

151 -

(°c)
150 ‘

1A9 —

1h6 «

I \

r

 

 

 

B-8

Fig. 12. Phase Diagrams for Isotactic
Poly(butene-l) - Butyl Cellosolv ---

rectilinear diameters.

B-7

 

0.06 0.'07

 

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A2

The values of the interaction parameters in the diethyl carbitol
system are 0 = 371.70K, E’ = 0.9hl for isotactic poly(butene—l) and
0 = 386.70K, 37= 0.h58 for atactic poly(butene-l).

For the butyl cellosolve system 0 is again higher for the atac—
tic isomer but the relative values of the entropy parameter are reversed.
The values obtained are e = 1160.11°K, 1!. 0.203 for isotactic poly(butene-l)
and e = 101.3011, ‘1 = 0.308 for the atactic polymer.

Refering to Figure 13 it will be noted that the curves have a
point of intersection at which the critical temperature is the same for
both stereoisomers. it1

According to theory (equation 7), the temperature dependence of

_ can be obtained from the interaction parameters. For atactic poly-
(butene-l) in diethyl carbitolX; = 0.01.2 + 177.1(1/T) and in butyl
cellosolve ZC= 0.192 + 1h5.2(l/T) for this isomer. The relationship

for isotactic poly(butene-l) is3t a -0.hhl + 3h9.8(l/T) in diethyl
carbitol and l(= 0.297 + 93.h6(1/T) in butyl cellosolve. These functions
are plotted in Figures 15 and 16.

For comparison of the two systems, the parameters are collected
in Table XIV.

Table XIV} The Thermodynamic Interaction Parameters for Isotactic and
Atactic Poly(butene-l) in Diethyl Carbitol and Butyl Cellosolve

 

 

 

 

Isomer Diethyl Carbitol Butyl Cellosolve
eggxz ‘3 0(0K) 1'

Atactic 386.7 0.h58 h71.3 0.308

Isotactic 371.7 0.9hl h60.h 0.203

Difference 15.0 0.583 10.9 0.105

 

 

0.8

0.7

0.6

0.5

0.1;

0.3

0.2

0.1

0.0

0.1

113

 

 

 

‘5 Isotactic
-r
Atactic
1r
1-
j-
d)-
Fig. 15. The Dependence of the Flory-Huggins Interaction
Parameter for the System, Poly(butene-l) - Diethyl Carbitol.
. f ‘ i
1.0 2.0 3.0 h.0

(1/1'3' x 103

 

 

0.9 a

0.8 ‘
0.7"
0.6 s

0.5 ‘

T

 

Atactic

 

sotactic

 

 

0.14 "'
0.3 hin-
002 ‘-
Fig. 16. The Dependence of the Flory-Huggins Interaction
0 1._ Parameter for the System, Poly(butene-l) - Butyl Cellosolve.
0'0 f 4. 1'.
1.0 2.0 3.0 h.0

(l/T) x 103

AS

The weights of known volumes of diethyl carbitol were determined
at h5°c., 61°C., 75°C. and 85°C. The calculated densities were fitted
by least squares giving the relationship

d - 0.931 - 0.0011(00).

The weights of known volumes of butyl cellosolve were determined
at 90°C., 10h°C., 132°C. and 1h0°C. Least squares gave the density temp-
erature relationship

d . 0.937 - 0.001T(°C).

Specific volumes of the isomers as calculated from.Natta's

dilatometric data are

vsp(atactic) = 1.15h + 9.0 x 10'4 (T(°C) - 30)

vsp(isotactic,1iquid) = 1.20 + 3.8 x 10’4 T(°C).

IV} DISCUSSION

Although the values of x are for a polymer of infinite molecular
weight, they can be used to show the trend for any molecular weight. XI
can be interpreted as a measure of solubility; therefore some statement
can be made about the relative solubilities of the two stereoisomers.

Consider first the diethyl carbitol system as given in Figure
15. .At temperatures above the point of intersection, which correSponds
to 8h°C., isotactic poly(butene-l) is the more soluble isomer and below
it the less soluble.

This situation is reversed in butyl cellosolve (Figure 16). The
atactic isomer is the more soluble at temperatures above the point of
intersection. Intersection here occurs at a much higher temperature,
213°C., which would be impossible to obtain experimentally since it is
above the boiling point of the solvent. These are hypothetical situ-
ations, of course, because the solubility at any temperature is a func-
tion of the molecular weight.

Although Krigbaum reports a higher theta temperature for iso—
tactic p01y(butene—l) than for the atactic isomer in anisole, the it
versus l/T curves are similar to the diethyl carbitol system as reported
here. An intersection occurs at 89°C. in this system and the differences
in solubility at other temperatures aren't as large as reported here
for diethyl carbitol.

The root mean square end to end distance cannot be calculated
from these data, but must be determined from light scattering measure-
ments. These phase studies do give an indication of what differences

might exist. At the 0 temperature, the polymer assumes its unperturbed
to

A?
dimensions. Since in both solvents investigated 0 is higher for atactic
poly(butene-l), its expansion factor, a, is smaller at a given temper-
ature; eg., at 0 for atactic its a is unity but the a for the isotactic
Species is greater than one (above its 0).

The heat of dilution parameter, a, is positive for both polymers
as is expected in poor solvents. In an ideal solution, the heat of
mixing is zero, and E can be used as a measure of deviation from ideality.
In diethyl carbitol isotactic poly(butene-l) has a larger 5 and so is
less ideal. There is a reversal in the relative values of the heat of
dilution and entropy parameters in butyl cellosolve. These differences
in the two systems studied are thought to reflect differences in size
and polarity of the solvent molecules.

These experiments indicate that differences in the thermodynamic
interaction parameters of stereoisomeric polymers are dependent on the
solvent as well as on the degree of stereoregularity of the polymer.

If the dependence on solvent is clarified and it is possible to
separate variables, differences in the thermodynamic interaction para-
meters might represent a quantitative measure of the degree of stereo-

regularity.

10.
11.
12.

13.

1h.

15.
16.

17.

l8.

19.

20.
21.

22.

V. REFERENCES
Flory, P. J. Principles of Polymer Chemistry, Cornell University
Press, Ithaca, N.Y., 1953.
Tompa, H. Polymer Solutions, Butterworth Publications, London, 1956.

Huggins, M. L. Physical Chemistry of High Polymers, John Wiley and
Sons, Inc., N.Y., 1958,IChap. 6.

 

Tempa, C. R. 28 Renunion. Soc. Chim. phys., Paris 163 (1952).
Flory, P. J. and W. R. Krigbaum, J. Chem. Phys., 18, 1086 (1950).

Schulz, G. V. and H. Craubner, Zeit. Elecktrochem, 63, 301-308
(1959).

V00rn, M. J., Fortschritte Der Hochpolymeren Forschung, 1.Band, 2.
Heft, Springereverlog (I959).

Kawai, T., Bull. Chem. Soc., Japan 22, 560—7(1956).
Schultz and Flory, J. Amer. Chem. Soc., 7g, 90 (1952).
Schultz and Flory, J. Amer. Chem. Soc., 15, 3888 (1953).
Schultz and Flory, J. Amer. Chem. Soc., 15, 5681 (1953).
Richards, R. B., Trans. Faraday Soc., Q2, 10 (l9h6).

Kinsinger, J. B. and R. E. Hughes, J. of Physical Chem., 63, 2002
(1959).

Danusso, F. and G. Moraglio, J. Polymer Sci., fig, 161 (1957).
Kinsinger, J. B., R. A. Wessling, J. Amer. Chem. Soc., 81, 2908 (1959).
Private Communication to J. B. Kinsinger.

Natta, G., G. Marzanti, G. Crespi and G. Moraglio, Chim. e Ind.
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