PHASE-BEHAVIOR OF THE MEMBRANE FORMING WATER-DMSO-EVAL COPOLYMER SYSTEM

The equilibrium phase behavior of ethylene vinyl alcohol (EVAL) copoly mer in mixtures of DMSO (dimethylsulfoxide, solvent) and water (nonsol vent) was studied for different temperatures. Both crystallization-ind uced gelation and liquid-liquid demixing were observed. From the deter mined phase diagram of this system at 25 degrees C, three regions may be identified, i.e., a homogeneous region, a gel region, and binodal r egion in which both types of phase transition rake place. At higher te mperatures, crystallization isotherm was found to intersect the binoda l phase boundary, which is analogous to the phase behavior reported by Stokes and Berghmans for several binary systems.