Solubility of Polystyrene Fractions -in Hvdroearbons J
J
J
u/
P. 0. POWERS Buttelle Memorial Institute, Columbus, Ohio
T h e precipitation points of four fractions of polystyrene have been measured i n mixtures of toluene and n-decane. Although the intrinsic viscosity of these fractions varied from 2.7 to 0.35, the solubility characteristics were not greatly different; low viscosity samples have a progressively greater solubility. The solubility characteristics of the fractions of 1.05 and 0.35 intrinsic viscosity were nearly identical. Solubility diagrams have been drawn for all four fractions in decane-toluene mixtures, and isotherms of Z O O , 50°, and 80" C. are shown. All samples showed a two-phase separation, and no fractions were particularly soluble in decane at ordinary temperatures. When
toluene was added, the solubility was increased. There was noticeable impro\ernent when the toluene content reached 40%; the fractions approached miscibility in all proportions a t 20" C. when the toluene content of the decane-toluene mixture reached 60%. The solubility of these fractions has been compared with expected behavior. Although the behavior agrees in a general way, quantitative agreement has not been established. The addition of a good solvent caiises a fraction to behave like a f r a c tion of lower molecular weight. T h e higher molecular weight materials in each fraction tend to characterize the solubility of the samplvs, particularly i n dilute solution.
E
samples of four viscosity ranges were used. To obtain sufirieiit material, feactions of near]!. the same viscosity were combined, but the samples consisted chiefly of one fraction. The fracttions used had intrinsic viscosit,ies of 2.72, 1.90, 1.02, and 0.35, and were designated as fractions 0,1, 3, and 5 , respectively, Toluene and n-decane (c.P.) from Humphrey Wilkinson, Im., were used. Solubility was estimated by hririgiiig a fraction into solution in toluene, adding n-decane to precipitation a t about 20" C., adding slight increments of decane, and determining the temperature a t which precipitation occurred on slow cooling. \Yhgn these temperatures reached 80" C., or above, toluene was again added until the precipitation temperature was lowered to 20."C. Decane was again added in increments and the cloud points were measured. This alternate addition of toluene and decane was continued until the resin content was less than 10%. Content of resin and solvents )vas calculated as volume per vent of the materials.
ARLIER studies (6, 6) have been made on the solubility of various samples of polystyrene in pure hydrocarbons and mixtures of hydrocarbons. Some of the earlier results indicated noticeable deviations from the solubility behavior predicted from a therniodynamic analysk of the expected behavior of high polymers in solution. Since the samples examined in the earlier studies were either unfractionated or rather crudely separated into fractions, this work was done t o determine the behavior of car.efully separated fractions of high molecular weight polystyrene. Solubility determinations on these fractions were made by determining the precipitation temperatures in mixtures of decane and toluene. MATERIALS
The polystyrene fractions mere prepared by Bartell (2) by precipitating a higher molecular weight polystyrene from a 2% solution in methyl ethyl ketone with propyl alcohol. Four fractions of nearly equal weight were collected. The fractions from the first aecipitatiou were redissolved and reprecipitated. Several suc reprecipitations were conducted, and for this study,
SOLUBILITY OF FRACTIONS
The precipitation points thus determined were plotted 011 t riaxial coordinates and from these points isotherms for 20°, 50". and 80" C. were chosen. Thcsc are shown in Figures 1 through
TOLUENE, %
TOLUENE, Yo
Figure 2.
Figure 1. Solubility of Fraction 0
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Solubility of Fraction 1
December 1950
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
TOLUENE,S,
Figure 3.
Solubility of Fraction 3
4 for the four fractions. Because of the high viscosity of the first three of these fractions, solubility determinations above 50% resin concentration are difficult to make, and curves are extrapolated from determined values. However, from comparison with solubility curves from earlier work (6, 6), where solubility was determined over the wholc range of resin concentration,
Figure 5.
40 RESIN, VOLUME % Solubility of Resins in 6 0 4 DecaneToluene
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TOLUENE, %
Figure 4.
Solubility of Fraction 5
it is felt that these curves represent a reasonably accurate estimate of the solubility at high solids. Comparison of the location of the isotherms in Figures 1 to 4 will show that a larger volume of toluene is required for a given isotherm as the intrinsic viscosity increases. Fraction 0 is measurably less soluble than fraction 1 which, in turn, is notice-
Figure 6.
60 40 20 RESIN, VOLUME % Solubility of Resins in 5 5 4 5 DecaneToluene '
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
Vol. 42, No. 12
80
,o' W-
a
3 50 + = I
tr
w
a.
5
w I-
20
Figure 8.
Figure 7.
RESIN, VOLUME % Solubility in 50-50 Decane-Toluene
80
Figure 9.
RESIN, VOLUME 7 0 Solubility in 45-55 Decane-Toluene
60
40
20
RESIN, VOLUME % Solubility of Resins in 40-60 DecaneToluene
ably less soluble than fraction 3. However, the difference in solubility between fractions 3 and 5 is slight. Figure 10. SOLUBILITY IN DECANE-TOLUENE MlXTURES
From Figures 1 to 4, the solubility diagrams shown in Figures 5 to 9 of fractions 0, 1, 3, and 5 at varims concentrations of toluene in the decane-toluene mixture have been drawn. I n all these figures, there is a similarity in the behavior of fractions 3 and
60 40 20 RESIN, VOLUME % Solubility of Resin 0 in Decane-Toluene Mixtures
80
5. Each addition of toluene improves the solubility of each of the fractions. When only 40% of toluene is present in the decanetoluene mixture, the fractions have very limited solubility. How-
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
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I*!
0.6
0.7
0.8
0
0.9
5 1.0 t.a
1.1
1.2
n RESIN Figure 12. Analysis of Tompa, r = 10 1.3
I .4
1.5
RESIN, VOLUME % Figure 11. Calculated Solubility Curves
ever, when tCa toluene content is raised t o SO%, the two lower fractions are miscible in all proportions at room temperature and a further increase in toluene content t o 68% will result in complete miscibility above 20’ C. for all fractions. Figure 10 is added t o show the effect of increasing toluene concentration (shown by the numbers on the curves) on the solubility of the least soluble of the polystyrene fractions. The critical resin concentration occurs a t higher solids content as the amount of toluene in the solvent mixture is increased. DISCUSSION
Comparison of the results of this study with the earlier work shows no major differences in the solubility diagrams resulting from more careful separation of the fractions. It has been shown (7) t h a t a mixture of polymers might be expected t o behave similarly to close-cut fractions. It is somewhat surprising that the two most soluble fractions i n this study were nearly alike in solubility characteristics. This suggests t h a t the least soluble fractions may greatly influence the solubility characteristics of a resin, particularly when measured (as in this investigation) by initiation of precipitation of the resin. It has recently been suggested that the initial precipitation is controlled by the number-average molecular weight. Unfortunately, these values are not available now for the fractions employed. Howevcr, because these were precipitated fractions, it may be expected that the number averages are not greatly different from the viscosity averuge.
It was hoped that a quantitative estimate of the solubility of the resins could be made from these results. This has not been possible up to the present. The studies of Flory (3)and Huggins (4) have analyzed conditions for precipitation of polymers. The author’s results, with certain exceptions noted in earlier papers, agree well in a qualitative manner with their predictions. The system of Flory is somewhat complicaced; it predicts a solubility diagram varying with molecular weight and with critical resin concentration a t low values with high molecular weights. As shown in Figure 10, high molecular weight polystyrene can have a critical resin concentration a t fairly high concentrations in a good solvent. The equation of Huggins ( 4 ) , Figure 11,
where and P, are the molal volume of the solvent and solute, respectively, vl and vz are the corresponding volume fractions, and p is the usual interaction constant, has been plotted for various values of V*/f‘l which may be regarded as a measure of molecular weight. Huggins’ family of curves bears a marked resemblance to the results of this paper. However, fractions used in the author’s study have calculated ( I ) molecular weights of 1,020,000,700,000, 260,000, and 71,000; thus, they behave in most instances like materials of much lower molecular weight. Huggins has shown that the p value may vary with temperature. p
= a
-+ a/?’
(2)
However, it has not been possible to fmd any regular variation of the values of a and with changes in temperature, solvent composition, or molecular weight of the resins. The analysis of Tompa (9) has predicted the behavior of polymers in mixtures of solvent and nonsolvent. Here again, the author finds much better agreement with the results of this paper when low values of Tompa’s constant, r , which varies with molecular weight of the resin, are used. The plot of solubility of it
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INDUSTRIAL AND ENGINEERING CHEMISTRY
polymer for which T = 10 is shown in Figure 12. The figures on the curve represent per cent solvent for various values of a, an interaction constant whose value may be expected to decrease with the temperature. A comparison of these curves with Figure 10 shows a remarkably parallel behavior. However, the critical resin concentration occurs at lower values. Scott ( 8 ) has recently analyzed the expected behavior of polymers in solvent-nonsolvent systems. This analysis could not readily be interpreted in terms of variation of temperature; hence, concentration diagrams have not been given. It has been previously noted that phase diagrams may be regarded as model plasticizer-resin systems (6,6). The difference in behavior with relatively smail changes in solvent-nonsolvent ratio is in agreement with the known sensitivity of plastic materials to chmges in plasticizer structure. The relative insolubility of polyvinyl chloride in nonyl phthalate as compared to octyl phthalate illustrates this sensitivity. A high molecular weight resin in a good solvent exhibits much the same solubility diagram as a low molecular weight resin in a poor solvent. It is reasonable that a good solvent acts, to a degree, as a monomer or a low polymer might act, and thus reduces
the effective degree of polymerization of the resin, whereas a poor solvent reduces by dilution the solvent effect of low polymers. ACKNOWLEDGMMENT
The author is indebted to Charles Bartell for the polystyrene used in this study and to Louis E. Novy who carried out much of the experimental work. LITERaTURE CITED
(1) Alfrey, T., Bartovics, A . , and Mark, H., J . Am. Chem. Soc., 65,
2349 (1943).
(2) Bartell, Charles, "Comparison of Methods of Frartionating
High Polymers," M S.thesis, Ohio State University, 1949.
(3) Flory, P. J., J . Chem. P h y s . , 12, 425 (1944). (4) Huggins, M., J . Am. Chem. Soc., 64, 1712 (1942). ( 5 ) Powers, P. O., ISD. ENQ.CHEM.,41, 126 (1949). (6) Ibid., p. 2213. (7) Scott, R. L., J . Chem. Phys.. 13, 172 (1945).
(8) Ibid., 17, 268 (1949). (9) Tompa, H., Trans. Faraday Soc., 45, 1142 (1949). RECEIVED May 3, 1950. Presented before the Division of Paint, Varnish, and Plastics Chemistry a t the 117th Meeting of the AMERICANCHEMICAL SOCIETY, Detroit, Mioh.
Effect of Air on. Banbury Breakdown of Low Temperature J
Polvmers J
G. J. TIGER', M. H. REICH, AND W. K. TAFT Government Laboratories, Ilniversity of Akron, Akron, Ohio Low temperature GR-S polymers have been reported to break down more slowly during Banbury mastication, to require higher peak power loads to mix with carbon black, and to develop higher temperatures during mixing and tubing operations than were previously encountered with GR-S made a t 122" F. On the basis of previous work and preliminary investigations conducted a t the Government Laboratories, University of Akron, which demonstrated the importance of sufficient oxygen for plastication, ais was introduced into a size B laboratory Banbury a t a high loading of 1475 grams (about 95% of capacity). By this means, polymers X-478, X-510, and X-530 prepared a t 41" F. were broken down a t rates comparable to those for GR-S and GR-S-10 treated similarly without air. All polymers were reduced to about 35 ML-4 viscosity i n 6
minutes. Under similar conditions in the Banbury but without air, either little or no softening or actual stiffening of the low temperature polymer owurred. The Banbury work showed t h a t better dispersion of the air with the polymer, such as was necessary to soften X-532 and X-535 adequately, increased the rate of breakdown. On the other hand, variation of the temperature of the air between 47" and 89" F. and of the rate of flow of air between 2.9 and 9.6 cubic feet per minute did not affect markedly the softening of the lot of X-478 tested. The mill processing, extrusion, and the physical properties of compounds of air-treated stocks compared favorably with those of the untreated mill-mixed stocks; the results of the treatment were similar to those obtained by the usual Banbury pretreatment of GR-S and GR-S-10.
T
essing. Chalmers (6) has listed the increased usage of internal mixers with high processing speeds and dump temperatures in excess of 300" F. as one of the factors tending to increase scorching or stiffening. I n contrast, others have reported (16) that low temperature polymers require no lowering of viscosity, require no more power to mix, and can be processed without difficulty. Various approaches to these problems have been advocated. Chemical plasticizers added in the same quantities used for standard GR-S and natural rubber (up Bo 0.270)may be dctrimental t o low temperature polymen because instead of increasing their plasticity, they tend t o enhance stiffening (SO). Davis (9) suggested the use of Pepton 22 (0,O'-dibenzamidcdiphenyl disulfide) as an effective softener of cold rubber. Stangor and Radcliff (30) have stated that high concentrations of
HE superior serviceability of low temperature polymer over standard GR-S and GR-S-10 in tire treads is generally recognized ; however, these advantages have been partially offset by difficulties encountered during processing (9,11, 16, 18, 26, 28,30,36, 38) in which polymer breakdown was desired. White (36') stated that GR-S made a t temperatures lower than 50" C. waa reported by most investigators to break down more slowly during plastication, require more power to mix with carbon black, develop higher temperatures during mixing, and develop higher tubing temperatures. Premastication of GR-S X-435, a 41" F. rubber, b y either one or two passes through a Gordon plasticator (18) resulted in some stiffening and actual increase in power consumption, rather than in a saving, in later proc1
Present address, Gladstone, N. .J.
