VAPOR-LIQUID-EQUILIBRIUM OF POLYMER PLUS SOLVENT MIXTURES BY THE CHAIN-OF-ROTATORS EQUATION OF STATE

Vapor-Liquid equilibrium (VLE) of polymer + solvent mixtures is descri bed by the chain-of-rotators (COR) equation of state (EOS) using segme nt parameters that are applicable to polymers of varying molecular wei ght. Segment parameters a and b are obtained from small molecules of t he same chemical structure as the polymer segment. The segment paramet er c is then obtained by fitting polymer pressure-volume-temperature ( PVT) data. van der Waals and free energy matching mixing rules are inv estigated to describe mixtures of various types. Excellent correlation of VLE data is obtained for all mixtures studied by using only one co nstant interaction coefficient for a, k(12), in the van der Waals mixi ng rule independent of temperature or polymer molecular weight. VLE pr edictions from the COR EOS by using van der Waals mixing rules with ze ro k(12) as well as by using UNIFAC free energy matched mixing rules a re presented. For the majority of systems studied, both predictive met hods gave better or equal results compared to the UNIFAC-FV model (FV = free volume).