Multicomponent Polymer Materials - American Chemical Society

3 Poly(2,6-dimethyl-1,4-phenylene Oxide) Blends Studied by Inverse Gas Chromatography Downloaded by HARVARD UNIV on October 27, 2015 | http://pubs.acs.org Publication Date: December 9, 1985 | doi: 10.1021/ba-1986-0211.ch003

A. C . SU and J. R. F R I E D Department of Chemical and Nuclear Engineering and the Polymer Research Center, University of Cincinnati, Cincinnati, O H 45221

Miscibility of blends of poly(2,6-dimethyl-1,4-phenylene oxide) (PMMPO) with polystyrene (PS) and poly(4-methylstyrene) (P4MS) has been investigated by inverse gas chromatography (IGC). The Flory interaction parameter determined for the PMMPO-PS blend at 270 °C was 0.21 ± 0.3. The lower portion of this range coincides with values reported from melting point depression measurements and recent small-angle neutron scattering (SANS) studies of this blend. In comparison, the value determined for PMMPO-P4MS was -1.21 ± 0.3; this value suggests a more favorable free energy of mixing for this blend. Conclusions drawn from earlier glassy state property measurements or consideration of the lattice fluid theory of Sanchez and Lacombe in the present work supports the conclusion of miscibility of this blend, but shows little distinction between the two. Critique of the IGC results is given in terms of the limitations inherent with this technique.

MISCIBILITY O F P O L Y S T Y R E N E (PS) and poly(2,6-dimethyl-l,4-phenylene oxide) ( P M M P O ) has been well documented by a variety of experimental techniques including thermal analysis (1, 2), magic-angle spinning N M R (3), and small-angle neutron scattering (SANS) (4-6). Recently, we re ported evidence from differential scanning calorimetry (DSC), density, and mechanical property measurements for the compatibility of P M M P O with poly(4-methylstyrene) (P4MS) (7). In this chapter, we report results of the measurement of the Flory interaction parameter ( χ ) of both P M M P O - P S and P M M P O - P 4 M S blends by use of inverse gas chromatog raphy (IGC) (8). Estimates of χ for P M M P O - P S blends were reported pre viously from melting point (Tm) depression measurements of P M M P O , which can undergo solvent-induced crystallization in solution or when cast from certain solvents. Shultz and McCullough (9) concluded that a value of 0065-2393/86/0211/0059$06.00/0 © 1986 American Chemical Society

In Multicomponent Polymer Materials; Paul, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1985.

60

MULTICOMPONENT POLYMER MATERIALS

approximately zero was consistent with the observed Tm depression of P M M P O in a ternary mixture with PS and toluene. In support of a near zero value for χ , K w e i and Frisch (10) later demonstrated that morphologi cal effects alone may account for the small Tm depression observed for high molecular weight P M M P O - P S

blends. These conclusions are consistent

with the small exothermic heat of mixing reported for this blend from solu tion calorimetric measurements (11-13) and from recent C O 2 sorption studies (14). In a recent SANS study, Maconnachie et al. (6) reported values of χ for deuterated P M M P O in a PS matrix that varied from - 0.033 to - 0.021 over a temperature range of 104 to 273 ° C . T h e dependence of the Downloaded by HARVARD UNIV on October 27, 2015 | http://pubs.acs.org Publication Date: December 9, 1985 | doi: 10.1021/ba-1986-0211.ch003

second virial coefficient on temperature was used to predict a θ tempera ture in the region of 345 ± 55 ° C .

Experimental Materiak. P M M P O was obtained as an additive-free powder from General Electric. Samples of PS and P 4 M S were obtained as pellets stabilized w i t h butylated hydroxytoluene [ B H T , 2,6-bis(l,l-dimethylethyl)-4-methylphenol] through the courtesy of Β . Z . Gunesin of M o b i l C h e m i c a l Company. Molecular weights determined by gel permeation chromatography ( G P C ) were reported previously (7). Weight-average molecular weights obtained by low-angle laser scattering measurements (Chromatix K M X - 6 photometer) are i n good agreement w i t h the G P C results. These values are 35,900, 226,000, and 308,000 for P M M P O , PS, and P 4 M S , respectively. Polymers used for I G C studies were purified by precipitation from dilute chloroform solution into a large volume ratio of methanol. Chromatography. Packings for I G C measurements were prepared by mak ing a slurry of Chromosorb Ρ (60:40 mesh, acid washed, and dimethyldichlorosilane ( D M C S ) treated calcinated diatomaceous earth) w i t h dilute chloroform solu tions of each of the three polymers and 50.1:49.9 weight ratios of P M M P O - P S and P M M P O - P 4 M S blends. Packings were dried at 70 ° C i n a vacuum for approxi mately 1 week. These packings were then loaded into sections of 0.25-in. O.D. stainless steel tubing about 3 ft i n length and conditioned overnight at about 285 ° C i n a Perkin-Elmer model 990 gas ehromatograph equipped w i t h a thermal conduc tivity (TC) detector. The weight of polymer stationary phase on the support was determined for each column by Soxhlet extraction i n chloroform over 4 days. F o r the five columns used i n this study, the weight ratios of polymer to support ranged from 0.0424 to 0.0729. The carrier gas used i n the I G C measurements was helium at a flow rate of approximately 5 m L / m i n as determined by a soap bubble flowme ter. Solute probes were reagent (or better) grade benzene, toluene, ethylbenzene, and ortho-, meta-, and para-xylenes. T y p i c a l sample sizes were 5 μ ΐ , for air and 2U2 •+ IO3V3)]

- 02ln(V»/i52) - «3ln(V°3/t>3)}/*2*3


(8)

62


Downloaded by HARVARD UNIV on October 27, 2015 | http://pubs.acs.org Publication Date: December 9, 1985 | doi: 10.1021/ba-1986-0211.ch003

Results and Discussion T o evaluate the consistency of the experimental procedures and the method of data analysis, I G C results for PS at 150 and 175 ° C were compared with those reported in the literature (23-25). Agreement was satisfactory as shown by comparison of weight fraction activity coefficients (a\lwi) at in finite dilution in Table I. Values of V°g and corresponding values of χ « (Equation 6) representing the interaction of the six probes used in the present study with PS, P4MS, and P M M P O are given in Table II. Values of V°g for each probe and X23 (Equation 8) calculated for the two blends, P M M P O - P S and P M M P O P4MS, at 270 ° C are given in Table III. F o r P M M P O - P S , the mean value of X23 averaged over the six probes was 0.21. Error bounds are estimated to be ± 0 . 3 and arise principally from probe variation, uncertainties in load ing determination, and inaccuracies associated with measurement of the relatively small retention volumes obtained at the high temperature used in this study. This result is consistent with the PVT measurements of P M M P O - P S blends by Zoller and Hoehn (18) at comparable temperatures at which a near zero excess free volume of mixing was reported. By comparison, the value of X23 of - 1.21 determined for P M M P O P4MS suggests a more favorable free energy of mixing at this temperature.

Table I. Weight Fraction Activity Coefficients in Polystyrene Ω

00

Ω ao at 175

at 150 °C

°C

Probe

This Study

Ref. 23

Ref. 24

Ref. 25

This Study

Ref. 23

Ref. 25°

Benzene Ethylbenzene Toluene

4.82 4.98 4.80

5.44 4.96 5.22

— 5.3

4.85 5.01 4.90

4.87 5.05 4.88

5.67 5.47 5.29

4.88 5.04 4.98

Note: Ω 00 = lim (αχίνογ). Wi~*0

"Average of values reported at 170 ° C and 180 ° C . Table II. Specific Retention Volumes and Interaction Parameters for Unblended Polymers V°g(mL/g) Probe

PS

P4MS

Benzene Ethylbenzene Toluene o-Xylene m-Xylene p-Xylene

2.25 3.85 3.09 4.42 3.87 3.82

3.90 6.67 5.09 7.70 6.81 6.58

PMMPO 5.09 8.65 6.77 9.87 8.61 8.58

PS

P4MS

0.01 0.19 0.10 0.23 0.24 0.24

-0.50 -0.33 -0.37 -0.29 -0.29 -0.27


PMMPO -0.83 -0.66 -0.72 -0.61 -0.59 -0.60

3.

su AND FRIED

IGC Studies of PMMPO

Blends

63

Table III. Specific Retention Volumes and Interaction Parameters for Blends K(mL/g) Probe

PMMPO-PS


Benzene Ethylbenzene Toluene o-Xylene m-Xylene p-Xylene

χί3

PMMPO-P4MS

3.43 6.00 4.81 7.10 6.11 6.02

3.04 5.56 4.36 6.40 5.77 5.78

PMMPO-PS 0.07 0.18 0.22 0.31 0.25 0.23

PMMPO-P4MS -1.51 -1.23 -1.17 -1.22 -1.12 -1.03

This result was unexpected because of our earlier study of the glassy state properties of these blends (7). These studies suggested a slightly more mar ginal compatibility state for P M M P O - P 4 M S when compared to P M M P O PS. Conclusions in that study were drawn primarily from density measure ments at ambient temperature and the associated mechanical property behavior of the two blends. Significant differences in miscibility between these two blends also would not be expected from consideration of the lattice fluid (LF) theory of Sanchez and Lacombe (26). T h e L F equation of state parameters for PS and P M M P O have been determined at 267 ° C from the PVT data of Zoller and Hoehn (18). F o r P4MS, for which PVT is not yet available, the equa tion of state parameters was obtained from the thermal expansion coeffi cient (a) determined from dilatometry measurements (19) and from the isothermal compressibility (β) estimated by the parachor method of M c G o w a n (27). Solubility parameters (δ) at 267 ° C also can be determined by use of the relationship δ -

(ΤαΙβ)112

(9)

Values of the close-packed mer volume (*>*), characteristic temperature (T*), characteristic pressure (P*), and solubility parameters are given in Table I V . As shown, the values for PS and P4MS are not greatly different. As discussed by Sanchez (26), miscibility is favored when the ratios of characteristic temperature (r = T * / T | ) and characteristic mer volumes (v =

ΡχΙνζ)

a

r

e

both greater than unity. As shown by values given in Table

Table IV. L F and Solubility Parameters Polymer PS P4MS PMMPO

τ*(κ) 835 853 763

P* (bar)

v* (cc/mol)

δ (cal/ce)

4196 4144 4632

16.6 17.2 13.7

8.72 8.73 8.86


64


Table V . Miscibility Criteria

\ΔΊ·\

Blend PMMPO-PS PMMPO-P4MS

72 90

1.094 1.118

V

\Δδ\

1.21 1.26

0.14 0.13

V , both P M M P O - P S and P M M P O - P 4 M S fulfill these conditions, and only small differences appear between the two. In addition, the difference in solubility parameters between P M M P O and PS and between P M M P O and Downloaded by HARVARD UNIV on October 27, 2015 | http://pubs.acs.org Publication Date: December 9, 1985 | doi: 10.1021/ba-1986-0211.ch003

P4MS is within typical critical bounds often cited as a criterion for miscibil ity of high molecular weight blends. That the solubility parameter theory may be a useful indicator of miscibility in these blends may not be totally unexpected because miscibility may be associated only with the dispersive interactions between the phenyl ring of PS and the phenylene ring of P M M P O (28). Specific reasons for the apparent difference between the interaction parameters determined for the P M M P O - P S and P M M P O - P 4 M S blends cannot be definitely identified at present. It should be noted that intrinsic limitations of the I G C technique make a strict quantitative evaluation of results questionable (29, 30). T h e most severe limitation may be the use of the original Flory expression for AGm.

If an alternative phenomenological

form is used to include the dependence of χ ί ; · on composition (22, 31), the apparent χ 2 3 obtained from I G C measurements can be shown to be a func tion of X23, xu, and the derivative of X23 with respect to Φ2 from which X23 cannot be easily resolved (32). This result would explain the usually signifi cant variation of X23 with the choice of probe that is often attributed to specific interactions of the probe with one blend component or the occur rence of nonrandom mixing (29). This variation is typically handled by av eraging values as was done in this study. In this study, probes were selected with chemical structures comparable to that of the PS component, and, therefore, probe variation of χ 2 3 values was minimized. Further compari son of the miscibility state of these two blends by alternate and less ambigu ous techniques that eliminate the need of a solute probe, such as heat of mixing measurements of low molecular blends (29) or measurement of X23 by neutron scattering (33), would be desirable.

Nomenclature a Bn

Activity Second virial coefficient of probe at Τ

F J

F l o w rate (Q) of carrier gas standardized to atmospheric pressure and corrected for Pw; F = Q (760/Po) [(P0 PW)IP0] Correction factor for gas compressibility; / = (3/2) [(Pi/PQ)2 - l]l [(PiiPo)3

-

l]


3.

su AND FRIED

mi

IGC Studies of PMMPO

Blends

65

Number of polymer chain segments expressed as the ratio of molar volumes of polymer to solute, VV V i

η

Number of molecules

Pi

Inlet pressure to gas chromatograph

P

Outlet pressure of gas chromatograph

P

Vapor pressure of water at T

Ρι

Vapor pressure of pure probe at Τ

0

w

a

R tN

Ideal gas constant Net retention time; the time between the appearance of the nonin-


teracting (air) and solute probe peaks as measured at peak maxima Τ

C o l u m n temperature

Τ

Ambient temperature

Vi

Specific volume of polymer at Γ

V\

L i q u i d state molar volume of solute at Τ

a

V°g

Specific retention volume as normalized to 0 ° C

Wi

Weight fraction of polymer in the stationary phase

W

Total polymer weight of column

φ Xij X23

Volume fraction Flory interaction parameter Normalized interaction parameter for polymer-polymer blend; X*

=

(VVV2)X23

Literature Cited 1. MacKnight, W. J.; Karasz, F. E.; Fried, J. R. in "Polymer Blends"; Paul, D . R . ; N e w m a n , S., E d s . ; Academic: N e w York, 1978; Vol. 1, p. 185. 2. F r i e d , J. R. I n "Developments i n Polymer Characterization"; Dawkins, J. V., Ed.; A p p l . Sci.: L o n d o n , 1983; Vol. 4, p . 39. 3. Stejskal, E . O.; Schaefer, J.; Sefcik, M. D.; M c K a y , R. Α . ; Macromolecules 1981, 14, 276. 4. W i g n a l l , C . D.; C h i l d , H. R . ; L i - A r a v e n a , F . Polymer 1980, 17, 640. 5. Kambour, R. P.; Bopp, R. C.; Maconnachie, Α.; M a c K n i g h t , W. J. Polymer 1980, 21, 133. 6. Maconnachie, Α . ; Kambour, R. P.; W h i t e , D . M.; Rostami, S.; W a l s h , D. J. Macromolecules 1984, 17, 2645. 7. F r i e d , J. R . ; Lorenz, T.; Ramdas, A. Polym. Eng. Sci., i n press. 8. Lipson, J . E. G.; Guillet, J . E. I n "Developments i n Polymer Characteriza t i o n " ; D a w k i n s , J . V.; Ed.; A p p l . Sci.: L o n d o n , 1982; Vol. 3, p . 33. 9. Shultz, A. R . ; M c C u l l o u g h , C. R. J. Polym. Sci. Polym. Phys. Ed. 1972, 10, 307. 10. K w e i , T. K.; Frisch, H. L. Macromolecules 1978, 11, 1267. 11. Weeks, F . E.; Karasz, F . E.; M a c K n i g h t , W. J . J. Appl Phys. 1977, 48, 4068. 12. Karasz, F . E.; M a c K n i g h t , W. J . Pure Appl. Chem. 1980, 52, 409. 13. R y a n , C . L.; P h . D . Thesis, U n i v . of Massachusetts, Amherst, 1980. 14. M o r e l , G.; P a u l , D. R. J. Membr. Sci. 1982, 10, 273. 15. Everett, D . H. Trans. Faraday Soc. 1965, 61, 1637. 16. Deshpande, D . D.; Patterson, D.; Schreiber, H. P.; Su, C. S. Macromolecules 1974, 7, 530.



66


17. Reid, R. C.; Prausnitz, J. M.; Sherwood, T . K. "The Properties of Gases and Liquids"; 3d ed.; McGraw-Hill: New York, 1977. 18. Zoller, P.; Hoehn, H . H . J. Polym. Sci. Polym. Phys. Ed. 1981, 20, 1385. 19. Gunesin, Β . Z. Mobil Chemical Company, personal communication. 20. Flory, P. J. "Principles of Polymer Chemistry"; Cornell Univ. Press: Ithaca, New York, 1971. 21. Scott, R. L . J. Chem. Phys. 1949, 17, 279. 22. Al-Saigh, Ζ . Y . ; Munk, P. Macromolecules 1984, 17, 803. 23. Newman, R. H.; Prausnitz, J. M . J. Phys. Chem. 1972, 76, 1492. 24. Olabisi, O . Macromolecules 1975, 8, 316. 25. Schuster, R. H.; Grater, H.; Cantow, H.-J. Macromolecules 1984, 17, 619. 26. Sanchez, I. C . In "Polymer Blends"; Paul, D . R.; Newman, S., Eds.; Aca demic: New York, 1978; Vol. 2, p. 115. 27. McGowan, J. C . Polymer 1967, 8, 58. 28. Wellinghoff, S. T . ; Koenig, J. L . ; Baer, E . J. Polym. Sci. Polym. Phys. Ed. 1977, 15, 1913. 29. Walsh, D . J.; Higgins, J. S.; Rostami, S.; Weeraperuma, K. Macromolecules 1983, 16, 391. 30. Doube, C . P.; Walsh, D . J. Eur. Polym. J. 1981, 17, 63. 31. Narasimhan, V . ; Burns, C . M.; Huang, R. Y. M . In "Polymer Blends and Composites in Multiphase Systems"; Han, C . D . , E d . ; A D V A N C E S IN CHEMISTRY SERIES No. 206, ACS: Washington, D . C . , 1984; p. 3. 32. Su, A . C.; Fried, J. R. J. Polym. Sci., Polym. Lett. Ed., in press. 33. Hadziioannou, G . ; Stein, R. S. Macromolecules 1984, 17, 567.

RECEV IED for review January 7, 1985.ACCEPTEDMarch 11, 1985.


Multicomponent Polymer Materials - American Chemical Society

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