Thermodynamics of Polymer Blends by Inverse Gas Chromatography

Chapter 9

Downloaded by GEORGE MASON UNIV on December 23, 2014 | http://pubs.acs.org Publication Date: April 24, 1989 | doi: 10.1021/bk-1989-0391.ch009

Thermodynamics of Polymer Blends by Inverse Gas Chromatography G. DiPaola-Baranyi Xerox Research Centre of Canada, 2660 Speakman Drive, Mississauga, Ontario L5K 2L1, Canada IGC was used to determine the thermodynamic m i s c i b i l i t y behavior of several polymer blends: polystyrene-poly(n-butyl methacrylate), poly(vinylidene fluoride)-poly(methyl methacrylate), and polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) blends. S p e c i f i c retention volumes were measured for a variety o f probes i n pure and mixed stationary phases of the molten polymers, and FloryHuggins interaction parameters were calculated. A generally consistent and r e a l i s t i c measure of the polymer-polymer interaction can be obtained with this technique.

The concept of blending two or more polymers to obtain new polymer systems i s attracting widespread interest and commercial u t i l i z a t i o n . Blending provides a simpler and more economical a l t e r n a t i v e for obtaining polymeric systems with desired properties, as compared to the synthesis of new homopolymers. This growing demand for polymer blends has generated a need for a better understanding of the thermodynamics of m i s c i b i l i t y and phase separation in polymer systems. This in turn has generated tremendous interest i n techniques that can be used to characterize the thermodynamics of polymer-polymer systems. The usefulness of inverse gas chromatography for determining polymer-small molecule interactions i s well established (1,2). This method provides a fast and convenient way of obtaining thermodynamic data for concentrated polymer systems. However, t h i s technique can also be used to measure polymer-polymer interaction parameters v i a a ternary solution approach (2). Measurements of s p e c i f i c retention volumes of two binary ( v o l a t i l e probe-polymer) and one ternary ( v o l a t i l e probe-polymer blend) system are s u f f i c i e n t to calculate Xp3'» Flory-Huggins interaction parameter, which i s a measure of the thermodynamic t n e

0097-6156/89/0391-0108$06.00/0 • 1989 American Chemical Society

In Inverse Gas Chromatography; Lloyd, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


9. DiPAOLA-BARANYl

Thermodynamics of Polymer Blends

109

m i s c i b i l i t y of two polymers. IGC has been used to study a variety of blends. Some of these include polystyrenepoly(dimethyl siloxane) (4), polystyrene-poly(vinyl methyl ether) (S>6), poly(methyl acrylate)-poly(epichlorohydrin) ( J ) , poly(vinylidene f l u o r i d e ) - poly(ethyl acrylate) (8), poly(e-caprolactone)-poly(vinyl chloride) (2*1Q)> and poly(dimethyl siloxane)- polycarbonate (JJ.). This paper reviews the application of IGC in determining interaction parameters for three polymer blend systems: polystyrene-poly(n-butyl methacrylate) (PS-PnBMA), polystyrenepoly(2,6-dimethyl-1,4-phenylene oxide) (PS-PPO), and poly(vinylidene fluoride)-poly(methyl methacrylate) (PVF2-PMMA) (12-14). In each case, a generally consistent and r e a l i s t i c measure of the polymer-polymer interaction i s obtained. Materials and Methods Materials. A l l solutes were chromatographic quality or reagent grade and were used without further p u r i f i c a t i o n . The polystyrene samples (PS: M = 110,000, M /M ) of the Flory-Huggins theory, that the o v e r a l l interaction parameter between the v o l a t i l e probe (1) and the binary stationary phase (2,2) i s given by 2

2

2

2

X

1(23

) = In([273.16R(w v 2

- d - T O s "

2+

2

w v )/V p°V ]-(l-V /V ) , 0

3

3

( B

g

V

Pi u " .

1

1

2

4

2

) / R T

where w and wg refer to the weight fractions of each polymer in the blend. The volumetric data for the blends were determined by assuming that the s p e c i f i c volume of the blend i s the average of the s p e c i f i c volumes of the parent homopolymers (26-29). 2


(3)

9.

DiPAOLA-BARANYI

111


Results and Discussion Polymer-polymer interaction parameters ( x 3 ' ) were calculated using the following expression: 2

X«28) 12^2 + X 4> - X3*4>4>3 =

X

13

3

2

2

( 4 )

where 1 refers to the probe, 2 and 3 refer to the polymers in the stationary phase, (j> and g refer to the volume f r a c t i o n of each of the polymers, and x 3 = X 3 V l / V , where V1 and V refer to the molar volume of the polymers. The value of x 3 i s thus normalized to the size of the probe molecule. A negative interaction parameter i s required in order to ensure m i s c i b i l i t y of two high molecular weight polymers. Polymer-polymer interaction parameters are summarized for three systems: 1. blends of oligomeric polystyrene ( P S L ) and poly(n-butyl methacrylate) (15 to 80 wt-Jt P S L ) at 140°C; 2. blends of polystyrene and poly(2,6-dimethy1-1,4-phenylene oxide) (25 to 85 wt-% PS) at 240°C; and 3. blends of semi-crystalline poly(vinylidene fluoride) and poly(methyl methacrylate) (25 to 90 wt-Jt P V F ) at 200°C. Tables I to III summarize the x 3 values obtained with a variety of probes for each of these systems. 2

2

f

2

2

2


2

f

2

2

TABLE I.

f

Polymer-Polymer Interaction Parameters ( x 3 ) for Various PSL-PnBMA Blends a t 140°C 2

Wt-%PS

!

L

Solute 15

27

30

35

40

58

80

n-octane

-0.11

0. 10

0.42

-0.21

0.01

0. 11

0 07

2,2,4-trimethylpentane

-0.25

0. 09

0.47

-0.21

0.02

0. 19

0 .14

n-decane

-0.22

0. 10

0.40

-0.20 -0.01

0. 06

0 00

3,4,5-trimethylheptane

-0.21

0. 12

0.43

-0.18

0. 07

0 .06

cyclohexane

-0.25

0. 04

0.44

-0.24 -0.03

0. 07

0 04

benzene

-0.17

0. 11

0.47

-0.20

0. 05

0 .00

carbon tetrachloride

-0.22

0. 05

0.45

-0.24 -0.02

0. 09

0 .08

chloroform

-0.25

0. 09

0.41

-0.21 -0.03

0. 09

0 .01

2-pentanone

-0.30

0. 08

0.40

-0.25 -0.06

0. 02 -0 .09

1-butanol

-0.41

0. 06

0.35

-0.32 -0.08 -0 .01 -0 .03

n-butyl acetate

-0.25

0. 08

0.43

-0.23 -0.08

0.03

0.00

0. 04

0 .08

Source: Reprinted from ref. 12. Copyright 1981 American Chemical Society.


INVERSE GAS CHROMATOGRAPHY

TABLE I I . Polymer-Polymer Interaction Parameters (X23 ) f o r Various PS/PPO Blends a t 240°C 1

wt-% PS Solute


n-octane

25

50

75

85

0.46

0.38

-0.52

-0.55 -0.40

n-decane

0.38

0.53

-0.36

3,4,5-trimethylheptane

1.32

0.86

-0.03

0.07

n-butylcyclohexane

0.62

0.60

-0.32

-0.31

cis-decalin

0.74

0.71

-0.19

-0.06

toluene

0.47

0.51

-0.19

-0.06

n-butylbenzene

0.54

0.46

-0.34

-0.34

chlorobenzene

0.48

0.49

-0.31

-0.21

acetophenone

0.40

0.49

-0.23

-0.05

cyclohexanol

0.66

0.58

-0.03

0.17

Source: Reprinted with permission from ref. 13. Copyright 1985 Canadian Journal of Chemistry. TABLE I I I . Polymer-Polymer Interaction Parameters (X23') ° Various PVF2-PMMA Blends a t 200°C f

r

wt-% PVF2 Solute

25

50

75

90

acetophenone

0.55

-0.13

-0.51

-0.71

cyclohexanone

0.24

0.11

-0.33

-0.52

N,N-dimethylformamide

0.29

-0.20

-0.31

-0.45

cyclohexanol

0.03

-0.02

-0.46

-0.55

n-butylbenzene

0.12

0.01

-0.50

-0.59

o-dichlorobenzene

-0.01

-0.09

-0.50

-0.67

1-chlorooctane

0.06

0.08

-0.33

-0.60

1-chlorodecane

0.26

0.03

-0.47

-0.54

Source: Reprinted from r e f . 14. Copyright 1982 American Chemical Society.



9. DIPAOLA-BARANYI

Thermodynamics ofPolymer Blends

113

From these data, two general observations can be made. 1. As noted i n previous chromatographic investigations o f polymer-polymer m i s c i b i l i t y (2, 2, 10), some probe-to-probe variations are observed i n each of these systems. The work of Al-Saigh and Munk (I) and Pottiger (30) indicates that t h i s probe-to-probe v a r i a b i l i t y i s not i n t r i n s i c to the IGC technique, but i s probably a l i m i t a t i o n of the a b i l i t y of the modified Flory-Huggins theory to account for a l l polymer-probe interactions i n ternary solution systems (for example, inadequate expression for entropy of mixing which does not take into account non-random mixing of components). One might speculate that the probe-to-probe v a r i a t i o n may indeed r e f l e c t true changes i n interactions between the components o f the stationary phases, due to the variations in f o r c e - f i e l d s at contact interfaces brought on by nonrandom p a r t i t i o n i n g of the probe molecules. The IGC technique may be unique i n giving information on thermodynamic quantities as viewed from molecular, rather than bulk l e v e l s . 2. The X 2 3 ' parameter i s c l e a r l y dependent on the composition of the polymer blend. Examination of the tabulated data (Tables I to III) indicates that for each blend, a l l the probes y i e l d s i m i l a r trends. This composition dependence i s i l l u s t r a t e d graphically i n Figures 1 to 3, where each point represents the average X 2 3 * value for a l l the probes investigated for each blend composition. (In the PS-PPO system, the probe 3,4,5-trimethylheptane exhibited large deviations and was therefore not considered i n the averaging procedure.) This averaging procedure was employed i n order to circumvent the v a r i a b i l i t y i n the X 2 3 * values and to f a c i l i t a t e i l l u s t r a t i o n of the composition dependence. IGC studies (12-14) for each of these polymer blends reveal single, composition dependent Tg values (Figures 4-6), and i n the case of PVF2-PMMA blends, melting point depression i s also observed (Figure 7). These are taken as indicators of polymer compatibility. Blends of oligomeric polystyrene and poly(n-butyl methacrylate) are characterized by a large and unexpected variation of X 2 3 function of blend composition (at 140°C). The large fluctuation i n X 2 3 ' between 20 and 40 wt-# P S L i s d i f f i c u l t to explain. One of the referees has suggested that since the trend i s the same for a l l the probes, a possible error in the measurement of some quantity common to a l l probes, such as the determination of the amount of polymer on the column, could explain these fluctuations. This remains to be confirmed. Since the measured values of x 3 ' generally p o s i t i v e , i t appears that there are no strong a t t r a c t i v e forces between these two polymers which would favor m i s c i b i l i t y . However, because of the low molecular weight of the polystyrene, m i s c i b i l i t y i s permitted, even i n the presence of positive X 2 3 interaction parameters, due to favorable combinatorial entropy e f f e c t s . Increasing the molecular weight of polystyrene leads to an immiscible system (12). 1

a

s

a

a

r

e

2

1


114

INVERSE GAS C H R O M A T O G R A P H Y


o

20

40 WT - %

Figure 1.

Figure 2.

60 PS

80

100

L

n

Composition dependence of X23* * PSL~PnBMA blends. (Reproduced from r e f . 12. Copyright 1981 American Chemical Society.)

40

60

WT-%

PS

100

Composition dependence of X23 i PS-PPO blends (Reproduced with permission rrom Ref. 1 3 . Copyright 1985 Canadian Journal of Chemistry.) 1

R



DiPAOLA-BARANYl


100 PVF

WT-%

Figure 3.

2

Composition dependence of X23 * PVF2-PMMA blends. (Reproduced from r e f . 14. Copyright 1982 American Chemical Society.) 1

N

P S - P n B M A Blends L

0.2

W

Figure 4.

0.6

0.4 P

S

0.8

1.0

L

Composition dependence of Tg of PSL-PnBMA blends. (Reproduced from r e f . 12. Copyright 1981 American Chemical Society.)



116


Figure 5.

Composition dependence of Tg o f PS-PPO blends. (Reproduced with permission from Ref. 13. Copyright 1985 Canadian Journal of Chemistry.)



DiPAOLA-BARANYI

Thermodynamics ofPolymer Blends

0.2

0.4 W

Figure 6 .

0.6

PVF

1.0

2

Composition dependence of T of PVF2-PMMA blends. (Reproduced from r e f . 14. Copyright 1982 American Chemical Society.) g

0.4

0.6 WRVF

Figure 7.

0.8

0.8

1.0

2

Composition dependence of T of PVF2-PMMA blends. (Reproduced from r e f . 14. Copyright 1982 American Chemical Society.) m



118


Polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) blends with a high polystyrene content (>60 wt-J PS) are characterized by small negative interaction parameters (approximately -0.2) i n the molten state. This i s in accordance with the compatibility of PS-PPO blends. Small negative interaction parameters (< -0.1) have previously been reported for PS-PPO blends from melting point depression (31-33) and small-angle neutron scattering measurements (34)In addition, calorimetric studies have indicated a small negative enthalpy o f mixing for t h i s system at room temperature (35). In the present study, blends with low polystyrene content (

Thermodynamics of Polymer Blends by Inverse Gas Chromatography

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