Random homogeneous sodium sulfonate polysulfone ionomers: Preparation,characterization, and blend studies

The sodium salts of randomly sulfonated polysulfone (Na-SPSF), derived from 1,1′-sulfonylbis-4-chlorobenzene] with 4,4′-(1-methylethylidene)-bis-phenol], were prepared over the composition range of 3–30 mol% sodium sulfonate, using improved procedures in which the sulfonating complex was introduced into an intensely agitated polymer solution. In contrast to earlier work, T_g was found to increase nonlinearly with sodium sulfonate content. A SAXS study provided no evidence of ionic clustering in these polymers. Binary blends of Na-SPSFs differing only in composition were prepared by casting films from solution, and their phase behavior was studied by dynamic mechanical analysis after annealing at 250°C. It was found that the blends were miscible up to a composition difference of about 9–10 mol% sodium sulfonate. Using this fact it was possible to calculate a value for χ_ABn of 200–250, where χ_AB represents the segmental interaction parameter between unmodified and modified repeat units, and n is the degree of polymerization. Uncertainty in the degree of ionic association places a degree of uncertainty on the effective value of n and therefore on χ_AB. The product, however, is independent of any assumptions regarding molecular associations.