The effects of transesterification on the miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6‐naphthalate) were studied. Blends were obtained by solution precipitation at room temperature to avoid transesterification during blend preparation. The physical blends and transesterified products were analyzed by wide‐angle x‐ray scattering, differential scanning calorimetry, and nuclear magnetic resonance spectroscopy. It was found that the physical blends are immiscible and when the extent of transesterification reaches 50% of the completely randomized state, independent of blend composition, the blends are not crystallizable and show a single glass transition temperature between those of starting polymers. The interchange reactions were significantly influenced by annealing temperature and time but negligibly by blend composition. © 1996 John Wiley & Sons, Inc.

ABSTRACT:The cloud point curves for polysulfone (PSf)/solvent/water systems were determined by a titration method. A small amount of water was needed to induce liquid-liquid demixing and the temperature effect was small. From numerical calculations, it was found that the binary interaction parameters for the PSf/solvent/water system enlarges the homogeneous region in the phase diagram with a smaller nonsolvent-polymer interaction parameter x 13 , a greater nonsolvent-solvent interaction parameter x 12 , and a smaller solvent-polymer interaction parameter x 23 and the effect of polymer molecular weight was negligible except in the range of low molecular weight. The phase diagrams, calculated with constant x 12 that was chosen from the concentration-dependent interaction parameter g 12 value of the concentration range, were similar to the results obtained with g 12 . The slope of the tie lines indicated that demixing of the ternary system occurred at relatively similar nonsolvent concentration in both phases. A value of 2.7 for the water-PSf interaction parameter was obtained by fitting the experimental cloud point curve with the calculated binodal lines.

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Polyurethane membranes were prepared by an immersion precipitation process. The effects of dope concentration, coagulation bath composition, and the chemical structure of the polyurethane on the morphology of the membranes were studied. The degree of contraction was measured by quenching freshly formed polyurethane membranes in liquid nitrogen. A mechanism for the formation of membrane morphology during immersion precipitation is proposed.

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