Schuld, N. and Wolf, B. A.

"Solvent quality as reflectes in concentration and temperature dependent Flory-Huggins interaction parameters."

Journal of Polymer Science Part B: Polymer Physics 2001, 39, 651-662.

Abstract: Flory-Huggins interaction parameters c between poly(dimethylsiloxane) (Mw = 152 kg/mol) and different solvents (methyl ethyl ketone, toluene and n-octane) were determined as a function of composition and temperature by means of vapor pressure measurements. These data, complemented by independent information for dilute and very concentrated solutions, serve as the basis for a discussion of solvent quality by means of different theoretical relations. Irrespective of polymer concentration the chi values fall from methyl ethyl ketone via toluene to n-octane, identifying the ketone as the worst and the hydrocarbon as the best solvent. The variation of c with composition and temperature turns out to be complex. Within the range of moderate polymer concentrations the influences of composition decrease with increasing solvent quality. Additional effects become noticeable at the ends of the com-position scale. The enthalpy parts, chi_H, and the entropy parts, chi_S, of the Flory-Huggins interac-tion parameter, obtained from chi(T) , vary considerably with composition and change their sign in some cases; these constituents of the Flory-Huggins interaction parameter do not per-mit a direct assessment of solvent quality. A clear-cut picture is, however, regained upon a comparison of the interdependence of chi_S and chi_H. The elimination of explicit concentration influences re-establishes the order in solvent quality set up by means of chi.

preprint number: 214