LIQUID-LIQUID EQUILIBRIA FOR COPOLYMER MIXTURES FROM A PERTURBED HARD-SPHERE-CHAIN EQUATION OF STATE

A perturbed hard-sphere-chain (PHSC) equation of state for real copolymer mixtures is based on a modified form of Chiew's equation of state for athermal mixtures of heteronuclear hard-sphere chains. The PHSC equation of state includes a van der Waals perturbation whose parameters are related to the intermolecular potential as suggested by Song and Mason. In the present model, sequence distribution in a polymer is introduced only into the hard-sphere-chain reference state; attractive forces are averaged, independent of sequence distribution. Theoretical coexistence curves and miscibility maps were computed for binary random copolymer mixtures containing two or three kinds of segments. The PHSC equation of state can predict simultaneous occurrence of a lower critical solution temperature and an upper critical solution temperature in the temperature-composition phase diagram of high-molecular-weight copolymer blends. Theoretical and experimental coexistence curves and miscibility maps show good agreement for systems containing two kinds of segments.