PHASE-BEHAVIOR OF LCST AND UCST SOLUTIONS OF BRANCHY COPOLYMERS - EXPERIMENT AND SAFT MODELING

Phase boundaries for a series of poly(ethylene-propylene) copolymers h aving uniform structure but differing in molecular weight, from 800 to nearly 100,000, in various solvents are determined experimentally up to 200-degrees-C and 600 bar. Propylene, 1-butene, and 1-hexene are us ed as solvents. A free-volume sensitive LCST is found near the solvent critical point and an energy sensitive UCST is found away from the so lvent critical point. The effect of supercritical ethylene on the phas e behavior of these systems is investigated. Statistical Associating F luid Theory (SAFT) is used to model the phase behavior of these system s. SAFT was chosen because the parameters for the polymers can be calc ulated from generalized correlations based on the polymer molecular we ight. SAFT is able to correlate the experimental data accurately using only one binary interaction parameter that is polymer molecular weigh t dependent. In addition, calculations are shown using the polymer sol ution theory of Flory and Patterson.