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

Phase boundaries for a series of poly(ethylene-propylene) copolymers having 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 used as solvents. A free-volume sensitive LCST is found near the solvent critical point and an energy sensitive UCST is found away from the solvent critical point. The effect of supercritical ethylene on the phase behavior of these systems is investigated. Statistical Associating Fluid Theory (SAFT) is used to model the phase behavior of these systems. SAFT was chosen because the parameters for the polymers can be calculated from generalized correlations based on the polymer molecular weight. SAFT is able to correlate the experimental data accurately using only one binary interaction parameter that is polymer molecular weight dependent. In addition, calculations are shown using the polymer solution theory of Flory and Patterson.