PHASE-EQUILIBRIA OF POLY(ETHYLENE-CO-VINYL ACETATE) COPOLYMERS IN SUBCRITICAL AND SUPERCRITICAL ETHYLENE AND ETHYLENE-VINYL ACETATE MIXTURES

Experimental high-pressure phase equilibrium data (cloud point and coe xistence data) are reported for solutions of commercial poly(ethylene- co-vinyl acetate) samples in supercritical ethylene and ethylene-vinyl acetate (VA) mixtures, These data are correlated with an equation of state rooted in statistical associating fluid theory (SAFT). SAFT capt ures the effects of polymer MW, incorporated VA%, and free VA on the c loud point pressure, and on the size of the fluid-liquid miscibility g ap, over a broad range of temperatures (50-250 degrees C) and polymer concentrations. Free VA is found to behave as a cosolvent (lowering th e cloud point pressure), except at low temperatures (< 100 degrees C) and with low VA-containing copolymers, in which case free VA, if prese nt in large excess (> 70 wt.%), behaves as a polar antisolvent due to favorable self-interactions among the free VA molecules, SAFT predicts a shift in the phase transition type, from upper-critical-solution-te mperature (UCST), to upper-lower-critical-solution-temperature (U-LCST ) with increasing flee VA in the monomer mixture.