DENSITY-TUNED POLYOLEFIN PHASE-EQUILIBRIA .2. MULTICOMPONENT SOLUTIONS OF ALTERNATING POLY(ETHYLENE PROPYLENE) IN SUBCRITICAL AND SUPERCRITICAL OLEFINS - EXPERIMENT AND SAFT MODEL

Different phase transitions (LCST, UCST, VL, and VLL) in binary, ternary, and, quaternary olefin-polyolefin systems are found to be easily tuned with density. Polyolefin is alternating poly(ethylene-propylene), PEP for short. The PEP phase transitions are quantitatively related to pressure, temperature, solvent composition, and its size. For example, supercritical ethylene drastically reduces the mutual solubilities of comonomers and PEP and hence increases the minimum pressure needed for complete miscibility. This ethylene antisolvent effect is modeled with statistical associating fluid theory (SAFT). SAFT also predicts that LCST and UCST curves can merge into a single U-LCST curve upon increasing the size difference between the polymer and solvent. Furthermore, one internally consistent set of SAFT parameters can correlate LCST, VL, and VLL equilibria simultaneously, which has not been demonstrated before. SAFT is verified experimentally with new phase equilibrium data obtained in an optical variable-volume cell for ternary PEP solutions in propylene + ethylene, 1-butene + ethylene, and 1-hexene + ethylene.