- Email: [email protected]
Glass transition temperatures of copolymers of ethyl acrylate and vinylidene chloride
European Polymer Journal. Vol I I. pp. t49 to 151 Pergumon Press 1975 Printed in Great Britain.
GLASS TRANSITION TEMPERATURES OF COPOLYMERS OF ETHYL ACRYLATE AND VINYLIDENE CHLORIDE J. COMYN and R. A. FERNANDEZ School of Chemistry, Leicester Polytechnic, P.O. Box 143, Leicester LEI 9BH, England
(Received 4 July 1974)
Abstract Glass transition temperatures of poly(ethyl acrylate-vinylidene chloride) and reactivit.~ ratios for the copolymerization of the parent monomers are reported. All the copolymers have glass transition temperatures higher than those of polyethylacrylate or polyvinylidene chloride: the copolymer containing equal molar quantities of each monomer has the highest. The data are accounted 10r in terms of the fractions of AA, AB and BB diads contained in the copolymers.
lymers were dried to constant weight at about 60 on a vacuum line, this required several days and coincided with the final removal of the smell of ethyl acrylate. Copolymer compositions were found by chlorine analysis (Yarsle> Laboratories Ltd. or The National Physical LaboratoriesL Intrinsic viscosities were measured in tetrah>drofuran at 25 ° An attempt was made to produce an alternating copoly1 W(A) W(B) + --(l) met [12] by shaking together zinc chloride (I mole l, ethyl L to(A) L(B) acrylate (1 mole) and vinylidene chloride (2 moles) at frequent intervals over a period of 2 hr. Precipitation of copoHere To in the glass transition temperature of the copolymer occurred on addition of the mixture to methanol. The lymer a n d T0(A) a n d ~(B) are those of the correspond- copolymer was twice dissolved in tetrahydrofuran (THF) ing homopolymers. The weight fractions of A and B and precipitated with methanol. After the final precipiunits in the copolymer are W ( A / a n d W(B). tation, the liquid phase was shown to be free of zinc by testing with dithizone reagent. Fresh copolymer was white but This e q u a t i o n shows a gentle m o n o t o n i c curve when turned brown in a few hours. Because of this change. TO is plotted against W(A) a n d therefore is not applicrigorous drying was sacrificed, and was limited to four able to copolymer systems which show a maximum or hours on a vacuum line at room temperature. The copom i n i m u m glass transition temperature at some compolymer was not sufficiently stable to .justify transmission for sition ofcopolymer. Examples of the latter are poly(acchlorine analysis, rylonitrile-styrene) [4, 5], poly(ethyl acrylate-vinyliGlass transition temperatures were measured either by dene chloride) [6~ 7], poly(methyl acrylate-vinylidene differential scanning calorimetry {Perkin Elmer DSC-IB). chloride) [6-8]. a n d poly(methyl acrylate n-butyl- by dilatometry (using mercury as the confining liquidt or b~ methacrylate) [4] which show maxima a n d poly- using a torsion pendulum. The torsion pendulum consisted of a small brass bar susmethylmethacrylate-styrene) [4, 8, 9], poly(methylmethacrylate-acrylonitrile) [4, 8, 10] a n d poly(methyl- pended from a steel wire. the copolymer sample hung from the bar and to a retaining weight beneath it. A small mirror methacrylate-vinylchloride) [11] which show minima. fixed to the bar was employed in amplitude measurements New data are now presented for poly(ethylacrylatein conjunction with a galvanometer scalc and lamp. The vinylidene chloride) a n d interpreted in terms of the assembly was contained in an air thermostat: temperature fractions of AA, AB a n d BB diads in the copolymers. measurement was by a copper constantan thermocouple junction placed close to the sample, and a cable arrangement permitted excitation of the pendulum from outside the EXPERIMENTAL thermostat. The period of oscillation was about 3 sec. The Random copolymers were prepared from freshly distilled amplitudes of about ten successive swings ~erc recorded ethyl acrylate and vinylidene chloride, quantities of which Plots of log (amplitude) against the ordinal number of the were placed in a Pyrex ampoule together with about 0.2 per swing were linear, and plots of their gradients against temcent by weight of benzoyl peroxide. These ampoules were perature gave well-defined peaks, the maxima of which were sealed off under vacuum after being frozen three times in taken as the copolymer glass transition temperatures. Samliquid nitrogen. Polymerization was carried out in a water pies for the torsion pendulum were films measuring apbath at 60 °. Contents of the ampoules were poured into a proximately 30 x 2 x 0-05 mm cast from solution in THF large excess of methanol, or a methanol water mixture if the on to glass. Final removal of solvent was by vacuum drying ethyl acrylate content was high, and the precipitated copoover a period of several days. 149
The glass transition temperatures of copolymers often fit equations which are based on the assumption that a fixed a m o u n t of free volume is associated with each type of m o n o m e r unit. Such equations have been summarized by W o o d [1] a n d by Shen a n d Eisenberg [2]; an example is the e q u a t i o n of Fox [3] :
J. COMYNand R. A. FERNANDEZ
150
Table 1. Details of monomer feeds, copolymer compositions and glass transition temperatures Mole fraction of ethyl acrylate in monomer feed
Mole fraction of ethyl acrylate in copolymer
Yield (%)
0-098 0.198 0-309 0.524 0.611 0.669 0.743 0.783 0-802 0'849 0"855 0.900 0.952
0.095 0-178 0.300 0-515 0-601 0.661 0.717 0.780 0.813 0-838 0.835 0-892 0.948
I"1 18 2.7 2-3 1.9 1.4 1-7 1-3 2.9 1.9 2.0 1.5 2.4
0-117 0.243 0.310 0.400 0-488 0.588 0.808
Approx. 10% Approx. 40~ Approx. 40~o Approx. 40~o Approx. 40% Approx. 40~o Approx. 40~ Approx. 40%
0.050
Glass transition temperature (°K)
RESULTS Results are collected in Table 1. Ethyl acrylate is monomer A throughout. Copolymers in the upper part of Table 1 were prepared with the aim of measuring 5E
Method of measuring T.o
281 290 296 308
Pendulum Pendulum Pendulum Pendulum
298
Pendulum
278
Pendulum
275
Dilatometry
275 250
Dilatometry Pendulum
264 284 298 302 307 308 307 288
Dilatometry Dilatometry Dilatometry Dilatometry Dilatometry Dilatometry Dilatometry Dilatometry
[7] Intrinsic viscosity (dm3/g)
0.038 0-056 0.054 0"107 0.089 0-101 0"086
both reactivity ratios and glass transition temperatures, and their yields were low. The remaining copolymers in Table 1 were prepared with higher conversions. The Tg of polyvinylidene chloride was found to be 251 K by dilatometry, and the Ta of the copolymer
prepared in the presence of zinc chloride was 408 K by differential scanning calorimetry. The following reactivity ratios have been evaluated using the Fineman and Ross equation [13] and the method of least squares. rA = 0"95 + 0"02 rB = 1.11 + 0-12
/ /
A plot of glass transition temperatures against the composition of monomer feed, the latter being very close to the composition of copolymer in this case, is shown in Fig. 1.
\\\
DISCUSSION The fractions ofAA, BB and AB diads (here both AB and BA diads are regarded as being AB) in copolymers are given by Eqns. (2)-(4) [14]. 24( o
I
0.2
I
I
0.4
o.6
I
06
,.o
fA
Fig. 1. Dependence of the glass transition temperature of poly(ethyl acrylate-vinylidene chloride) the mole fraction of ethyl acrylate in the monomer feed. O Measured by dilatometry, • by torsion pendulum, • from ref. [4]. Broken line calculated from Eqn.(6)with Tg(AB) = 408 ° K, solid line from Eqn. (7) with Tg(AB) = 371° K.
r Af.~ fAA = rAf2 + 2fA(l -- fA) + "8(1 -- f~)Z
(2)
ra(1 - fA) 2 f . . = rAf~ + 2A(1 _ f , ) + rs(1 _ f.~)2
(3)
2fA(l - fA) fan = r , f Z + 2f~(l -- f~,) + ra(1 -- f.~)-'"
(4)
Glass transition temperatures If the basis of interpretation is to treat the copotvmer as a sequence of diads, then the Fox equation can be rewritten as: 1
W(AA)
W(AB)
T~,- T~(AA) + ~
W(BB)
(5)
+ T~(BB~'
where W(AA), W(AB) and W(BB) are the weight fractions of the respective diads, ~(AA) and ~(BB) are the glass transition temperatures of the corresponding homopolymers, and ~(AB) is that of an alternating copolymer of A and B. In this specific case where the diad masses are very similar, Eqn. (5) becomes 1 .f~, f,n3 7 " , - Tq(aa) + ~
,f*~ + Tq(AB-~)'
(6)
An alternative approach to glass transition temperattires is by the Gibbs-DiMarzio theory[15], from which the following equation [16] has been proposed for copolymers which are treated as a sequence of diads. L = .f~, Tq(AA) + fBB Tq(BB) + f~B ~(AB) (7) Equations (6) and (7) have been fitted to the experimental data by varying T~(AB) until the best fit was obtained. All other parameters in the equations are known, fAA, fBa and lAB being calculated from Eqns. (2)-(4). Our value of Tq(BB) is in good agreement with that of Illers [4], and Illers' value of To(AA) (246 K) is in concord with the data in Fig. 1. The best fit values of T~(AB) are 408 K for Eqn. (6), and 371 K for Eqn. (7). The lines calculated with these values are shown in Fig. 1. The excellent agreement of the former value x~ith that obtained for the copolymer prepared in the presence of zinc chloride is probably somewhat fortuitous, bearing in mind the uncertainties in the composition of this material. Both equations are capable of providing a reasonable fit to the experimental data. Depending on whether the free volume or GibbsDiMarzio viewpoint is taken, the increased To of the copolymers is brought about either by the small amount of free volume associated with the AB diad, or its increased stiffness. These properties of the AB diad are not an average of those of the AA diad or BB diad in either case. Irrespective of the viewpoint taken, the maximum Tq should coincide with the highest fraction o f A B diads. Differentiation of Eqn. (4) shows that this will occur at a value offA given by f d A B max) -
1 I q- (r~/rl~) 1 2'
(8)
Here the predicted value offa(AB max) is 0.52. Substitution of this equation into that of Fineman and Ross produces an equation of which F~ = 0.5 is a solution. So the maximum T~, (or minimum if the AB unit has a large associated free volume or low stiffness) should always occur when the copolymer contains
151
equal molar quantities of each monomer. This is supported by all the copolymers except one, listed in the introduction as having maximum or minimum To. Except for poly(methylmethacrylate-styrene), they all have their maximum or minimum at or very close to F,, = 0"5. The maximum attainable fraction of AB diads, f~,l~ (max), is obtained from Eqns. (4) and (8) and is .f~dmax) -
1
1 + (r~rl¢ I ~"
(9)
So the maximum value of T, should vary with the product of the reactivity ratios. It may be for this reason that our ~s values are somewhat higher than those of Powell et a l . [ 6 , 7 ] : our maximum T,, is 308°K whilst theirs is 299 ° K: our polymerizations were in bulk, theirs in emulsion. To account for this difference, the value ofrAr~ in emulsion would need to be 1-9; our bulk value is 1-05. However, it is possible that plasticization by residual emulsifier might lower T~ for the emulsion polymer. There is some evidence that r 4 ~ may vary with the mode ofcopolymerization: for the copolymerization of styrene and methylmethacrylate, r xr~ has been reported[17] as 0.22 in solution and 028 in emulsion; Sweeting et al. [18] corrected the apparent reactivity ratios of the emulsion copolymerization of acrylonitrile and vinylidene chloride for water solubility of monomers and quoted rarl~ = 0228 while in bulk a reported value is 0-337 [19]. REFERENCES
1. L. A. Wood, d. Poh'm. Sci. 28, 319 (1958).
2. M. Shen and A. E]senberg, Pro.q. Solid-State Chem. 3, 407 (1966). 3. T. G. F,ox, Bull. Am. phys. Soc. l, 123 (1956). 4. K. H. fliers, Bet. 70, 353 (1966). 5. R. B. Beevers and E. F. T. White, J. Polym. Sci. BI, 171 (1963). 6. E. Powell and B. G. Elgood, Chemy bid. 90l (1966). 7. E. Powell, M. J. Clay and B. J. Saunston. J. Appl. Polym. Sci. 12, 1765 (1968). 8. K. H. Illers, Kolloidzeitschr!/t 190, 1611963). 9. R. B. Beevers, Trans. Faraday Soc. 58, 1465 (1962). 10. R. B. Beevers and E. F'. T. White. 7~'ans. Faraday Soc. 56, 1529 (19601. 11. N. W. Johnston, J..'qacromol. Sci. A7, 531 (1973). 12. S. Tazuke, Progr. Polym. Sci. Jap. 1, 69 (1971). 13. M. Fineman and S. D. Ross, J. Polym. Sci. 5, 259 (1950). 14. F. T. Wall, J. Am. chem. Soc. 66, 2050(1944). 15. E. A. DiMarzio and J. H. Gibbs, J. Polvm. Sci. 40, 121 (1959). 16. I. Uematsu and K. Honda. Rep. Prowl. Polym. Phys. Jap. 8, 111 (1965). 17. F'. T. Wall, R E. Florin and C. J. Belbecq, J. Am. chem. Soc. 72, ~,769 (1950). 18. L. Marker, O. J. Sxveeting and J. G. Wepsic, J. Polym. Sci. 57,855 (1962). 19. F. M. Lewis, F. R. Mayo and W. F. Hulse. J. Am. chem. Soc. 67, 1701 (1945).
GLASS TRANSITION TEMPERATURES OF COPOLYMERS OF ETHYL ACRYLATE AND VINYLIDENE CHLORIDE J. COMYN and R. A. FERNANDEZ School of Chemistry, Leicester Polytechnic, P.O. Box 143, Leicester LEI 9BH, England
(Received 4 July 1974)
Abstract Glass transition temperatures of poly(ethyl acrylate-vinylidene chloride) and reactivit.~ ratios for the copolymerization of the parent monomers are reported. All the copolymers have glass transition temperatures higher than those of polyethylacrylate or polyvinylidene chloride: the copolymer containing equal molar quantities of each monomer has the highest. The data are accounted 10r in terms of the fractions of AA, AB and BB diads contained in the copolymers.
lymers were dried to constant weight at about 60 on a vacuum line, this required several days and coincided with the final removal of the smell of ethyl acrylate. Copolymer compositions were found by chlorine analysis (Yarsle> Laboratories Ltd. or The National Physical LaboratoriesL Intrinsic viscosities were measured in tetrah>drofuran at 25 ° An attempt was made to produce an alternating copoly1 W(A) W(B) + --(l) met [12] by shaking together zinc chloride (I mole l, ethyl L to(A) L(B) acrylate (1 mole) and vinylidene chloride (2 moles) at frequent intervals over a period of 2 hr. Precipitation of copoHere To in the glass transition temperature of the copolymer occurred on addition of the mixture to methanol. The lymer a n d T0(A) a n d ~(B) are those of the correspond- copolymer was twice dissolved in tetrahydrofuran (THF) ing homopolymers. The weight fractions of A and B and precipitated with methanol. After the final precipiunits in the copolymer are W ( A / a n d W(B). tation, the liquid phase was shown to be free of zinc by testing with dithizone reagent. Fresh copolymer was white but This e q u a t i o n shows a gentle m o n o t o n i c curve when turned brown in a few hours. Because of this change. TO is plotted against W(A) a n d therefore is not applicrigorous drying was sacrificed, and was limited to four able to copolymer systems which show a maximum or hours on a vacuum line at room temperature. The copom i n i m u m glass transition temperature at some compolymer was not sufficiently stable to .justify transmission for sition ofcopolymer. Examples of the latter are poly(acchlorine analysis, rylonitrile-styrene) [4, 5], poly(ethyl acrylate-vinyliGlass transition temperatures were measured either by dene chloride) [6~ 7], poly(methyl acrylate-vinylidene differential scanning calorimetry {Perkin Elmer DSC-IB). chloride) [6-8]. a n d poly(methyl acrylate n-butyl- by dilatometry (using mercury as the confining liquidt or b~ methacrylate) [4] which show maxima a n d poly- using a torsion pendulum. The torsion pendulum consisted of a small brass bar susmethylmethacrylate-styrene) [4, 8, 9], poly(methylmethacrylate-acrylonitrile) [4, 8, 10] a n d poly(methyl- pended from a steel wire. the copolymer sample hung from the bar and to a retaining weight beneath it. A small mirror methacrylate-vinylchloride) [11] which show minima. fixed to the bar was employed in amplitude measurements New data are now presented for poly(ethylacrylatein conjunction with a galvanometer scalc and lamp. The vinylidene chloride) a n d interpreted in terms of the assembly was contained in an air thermostat: temperature fractions of AA, AB a n d BB diads in the copolymers. measurement was by a copper constantan thermocouple junction placed close to the sample, and a cable arrangement permitted excitation of the pendulum from outside the EXPERIMENTAL thermostat. The period of oscillation was about 3 sec. The Random copolymers were prepared from freshly distilled amplitudes of about ten successive swings ~erc recorded ethyl acrylate and vinylidene chloride, quantities of which Plots of log (amplitude) against the ordinal number of the were placed in a Pyrex ampoule together with about 0.2 per swing were linear, and plots of their gradients against temcent by weight of benzoyl peroxide. These ampoules were perature gave well-defined peaks, the maxima of which were sealed off under vacuum after being frozen three times in taken as the copolymer glass transition temperatures. Samliquid nitrogen. Polymerization was carried out in a water pies for the torsion pendulum were films measuring apbath at 60 °. Contents of the ampoules were poured into a proximately 30 x 2 x 0-05 mm cast from solution in THF large excess of methanol, or a methanol water mixture if the on to glass. Final removal of solvent was by vacuum drying ethyl acrylate content was high, and the precipitated copoover a period of several days. 149
The glass transition temperatures of copolymers often fit equations which are based on the assumption that a fixed a m o u n t of free volume is associated with each type of m o n o m e r unit. Such equations have been summarized by W o o d [1] a n d by Shen a n d Eisenberg [2]; an example is the e q u a t i o n of Fox [3] :
J. COMYNand R. A. FERNANDEZ
150
Table 1. Details of monomer feeds, copolymer compositions and glass transition temperatures Mole fraction of ethyl acrylate in monomer feed
Mole fraction of ethyl acrylate in copolymer
Yield (%)
0-098 0.198 0-309 0.524 0.611 0.669 0.743 0.783 0-802 0'849 0"855 0.900 0.952
0.095 0-178 0.300 0-515 0-601 0.661 0.717 0.780 0.813 0-838 0.835 0-892 0.948
I"1 18 2.7 2-3 1.9 1.4 1-7 1-3 2.9 1.9 2.0 1.5 2.4
0-117 0.243 0.310 0.400 0-488 0.588 0.808
Approx. 10% Approx. 40~ Approx. 40~o Approx. 40~o Approx. 40% Approx. 40~o Approx. 40~ Approx. 40%
0.050
Glass transition temperature (°K)
RESULTS Results are collected in Table 1. Ethyl acrylate is monomer A throughout. Copolymers in the upper part of Table 1 were prepared with the aim of measuring 5E
Method of measuring T.o
281 290 296 308
Pendulum Pendulum Pendulum Pendulum
298
Pendulum
278
Pendulum
275
Dilatometry
275 250
Dilatometry Pendulum
264 284 298 302 307 308 307 288
Dilatometry Dilatometry Dilatometry Dilatometry Dilatometry Dilatometry Dilatometry Dilatometry
[7] Intrinsic viscosity (dm3/g)
0.038 0-056 0.054 0"107 0.089 0-101 0"086
both reactivity ratios and glass transition temperatures, and their yields were low. The remaining copolymers in Table 1 were prepared with higher conversions. The Tg of polyvinylidene chloride was found to be 251 K by dilatometry, and the Ta of the copolymer
prepared in the presence of zinc chloride was 408 K by differential scanning calorimetry. The following reactivity ratios have been evaluated using the Fineman and Ross equation [13] and the method of least squares. rA = 0"95 + 0"02 rB = 1.11 + 0-12
/ /
A plot of glass transition temperatures against the composition of monomer feed, the latter being very close to the composition of copolymer in this case, is shown in Fig. 1.
\\\
DISCUSSION The fractions ofAA, BB and AB diads (here both AB and BA diads are regarded as being AB) in copolymers are given by Eqns. (2)-(4) [14]. 24( o
I
0.2
I
I
0.4
o.6
I
06
,.o
fA
Fig. 1. Dependence of the glass transition temperature of poly(ethyl acrylate-vinylidene chloride) the mole fraction of ethyl acrylate in the monomer feed. O Measured by dilatometry, • by torsion pendulum, • from ref. [4]. Broken line calculated from Eqn.(6)with Tg(AB) = 408 ° K, solid line from Eqn. (7) with Tg(AB) = 371° K.
r Af.~ fAA = rAf2 + 2fA(l -- fA) + "8(1 -- f~)Z
(2)
ra(1 - fA) 2 f . . = rAf~ + 2A(1 _ f , ) + rs(1 _ f.~)2
(3)
2fA(l - fA) fan = r , f Z + 2f~(l -- f~,) + ra(1 -- f.~)-'"
(4)
Glass transition temperatures If the basis of interpretation is to treat the copotvmer as a sequence of diads, then the Fox equation can be rewritten as: 1
W(AA)
W(AB)
T~,- T~(AA) + ~
W(BB)
(5)
+ T~(BB~'
where W(AA), W(AB) and W(BB) are the weight fractions of the respective diads, ~(AA) and ~(BB) are the glass transition temperatures of the corresponding homopolymers, and ~(AB) is that of an alternating copolymer of A and B. In this specific case where the diad masses are very similar, Eqn. (5) becomes 1 .f~, f,n3 7 " , - Tq(aa) + ~
,f*~ + Tq(AB-~)'
(6)
An alternative approach to glass transition temperattires is by the Gibbs-DiMarzio theory[15], from which the following equation [16] has been proposed for copolymers which are treated as a sequence of diads. L = .f~, Tq(AA) + fBB Tq(BB) + f~B ~(AB) (7) Equations (6) and (7) have been fitted to the experimental data by varying T~(AB) until the best fit was obtained. All other parameters in the equations are known, fAA, fBa and lAB being calculated from Eqns. (2)-(4). Our value of Tq(BB) is in good agreement with that of Illers [4], and Illers' value of To(AA) (246 K) is in concord with the data in Fig. 1. The best fit values of T~(AB) are 408 K for Eqn. (6), and 371 K for Eqn. (7). The lines calculated with these values are shown in Fig. 1. The excellent agreement of the former value x~ith that obtained for the copolymer prepared in the presence of zinc chloride is probably somewhat fortuitous, bearing in mind the uncertainties in the composition of this material. Both equations are capable of providing a reasonable fit to the experimental data. Depending on whether the free volume or GibbsDiMarzio viewpoint is taken, the increased To of the copolymers is brought about either by the small amount of free volume associated with the AB diad, or its increased stiffness. These properties of the AB diad are not an average of those of the AA diad or BB diad in either case. Irrespective of the viewpoint taken, the maximum Tq should coincide with the highest fraction o f A B diads. Differentiation of Eqn. (4) shows that this will occur at a value offA given by f d A B max) -
1 I q- (r~/rl~) 1 2'
(8)
Here the predicted value offa(AB max) is 0.52. Substitution of this equation into that of Fineman and Ross produces an equation of which F~ = 0.5 is a solution. So the maximum T~, (or minimum if the AB unit has a large associated free volume or low stiffness) should always occur when the copolymer contains
151
equal molar quantities of each monomer. This is supported by all the copolymers except one, listed in the introduction as having maximum or minimum To. Except for poly(methylmethacrylate-styrene), they all have their maximum or minimum at or very close to F,, = 0"5. The maximum attainable fraction of AB diads, f~,l~ (max), is obtained from Eqns. (4) and (8) and is .f~dmax) -
1
1 + (r~rl¢ I ~"
(9)
So the maximum value of T, should vary with the product of the reactivity ratios. It may be for this reason that our ~s values are somewhat higher than those of Powell et a l . [ 6 , 7 ] : our maximum T,, is 308°K whilst theirs is 299 ° K: our polymerizations were in bulk, theirs in emulsion. To account for this difference, the value ofrAr~ in emulsion would need to be 1-9; our bulk value is 1-05. However, it is possible that plasticization by residual emulsifier might lower T~ for the emulsion polymer. There is some evidence that r 4 ~ may vary with the mode ofcopolymerization: for the copolymerization of styrene and methylmethacrylate, r xr~ has been reported[17] as 0.22 in solution and 028 in emulsion; Sweeting et al. [18] corrected the apparent reactivity ratios of the emulsion copolymerization of acrylonitrile and vinylidene chloride for water solubility of monomers and quoted rarl~ = 0228 while in bulk a reported value is 0-337 [19]. REFERENCES
1. L. A. Wood, d. Poh'm. Sci. 28, 319 (1958).
2. M. Shen and A. E]senberg, Pro.q. Solid-State Chem. 3, 407 (1966). 3. T. G. F,ox, Bull. Am. phys. Soc. l, 123 (1956). 4. K. H. fliers, Bet. 70, 353 (1966). 5. R. B. Beevers and E. F. T. White, J. Polym. Sci. BI, 171 (1963). 6. E. Powell and B. G. Elgood, Chemy bid. 90l (1966). 7. E. Powell, M. J. Clay and B. J. Saunston. J. Appl. Polym. Sci. 12, 1765 (1968). 8. K. H. Illers, Kolloidzeitschr!/t 190, 1611963). 9. R. B. Beevers, Trans. Faraday Soc. 58, 1465 (1962). 10. R. B. Beevers and E. F'. T. White. 7~'ans. Faraday Soc. 56, 1529 (19601. 11. N. W. Johnston, J..'qacromol. Sci. A7, 531 (1973). 12. S. Tazuke, Progr. Polym. Sci. Jap. 1, 69 (1971). 13. M. Fineman and S. D. Ross, J. Polym. Sci. 5, 259 (1950). 14. F. T. Wall, J. Am. chem. Soc. 66, 2050(1944). 15. E. A. DiMarzio and J. H. Gibbs, J. Polvm. Sci. 40, 121 (1959). 16. I. Uematsu and K. Honda. Rep. Prowl. Polym. Phys. Jap. 8, 111 (1965). 17. F'. T. Wall, R E. Florin and C. J. Belbecq, J. Am. chem. Soc. 72, ~,769 (1950). 18. L. Marker, O. J. Sxveeting and J. G. Wepsic, J. Polym. Sci. 57,855 (1962). 19. F. M. Lewis, F. R. Mayo and W. F. Hulse. J. Am. chem. Soc. 67, 1701 (1945).