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Autori: Bercea M., Eckelt J., Wolf B.A
Editorial: Donald R. Paul, ACS Publications, Industrial &Engineering Chemistry Research, 47, p.2434-2441, 2008.
Vapor pressure data (at 50°C) of solutions of poly(methyl methacrylate) [PMMA], poly-styrene [PS] and of poly(styrene-ran-methyl methacrylate [P(S-ran-MMA)], with differ-ent weight fractions f of styrene units, in either CHCl3, acetone [AC], methyl acetate [MeAc] or toluene [TL] were evaluated with respect to the dependence of the Flory-Huggins interaction parameter on polymer concentration and on f. For all solutions under investigation, the Flory-Huggins interaction parameter varies considerably with the composition of the mixture and only for four of them [CHCl3/PS, AC/PMMA, MeAc/PS and TL/P(S-ran-MMA) f=0.5] this dependence is linear; another four systems exhibit a minimum [CHCl3/PMMA, CHCl3/P(S-ran-MMA) f=0.5, TL/PMMA and TL/PS] and only one [MeAc/PMMA] shows a maximum. With the exception of CHCl3/P(S-ran-MMA) and f=0.5 the Flory-Huggins interaction parametervalues of the copolymers do not fall reasonably between the data obtained for the corresponding ho-mopolymers. In most cases the incorporation of a small fraction of the monomer that interacts less favorably with a given solvent suffices to make the copolymer behave very similar to the worse soluble homopolymer. In order to rationalize these multifaceted findings we have modeled the results by means of an expression for the Flory-Huggins interaction parameter, which accounts explicitly for the chain connectivity of polymers and for the capability of the components to change their molecular conformation upon mixing. This approach yields a consistent picture of the present results; it reproduces the effects of polymer concentration on the Flory-Huggins interaction parameter quantitatively by means of three physically meaningful parameters. The modeling of the influences of copolymer composition requires one additional term for each of these parameters.
Cuvinte cheie: Flory Huggins interaction parameter, random copolymers, vapor pressure