Quasi-chemical approximation for nonrandomness in the hole theory of polymer systems comprising random copolymers

A modified version of Simha-Somcynsky's hole theory developed earlier is ad apted to obtain the equation of state and Helmholtz free energy for random copolymer systems and random copolymer/homopolymer blends. Miscibility beha vior of the blend of poly(styrene-co-p-bromostyrene)/polystyrene is investi gated to test the validity of the theory. With the molecular parameters ext racted from the experimental PVT data, not only a satisfactory description of the experimental PVT surfaces is obtained, but also the upper critical m iscibility behavior of the blend is predicted, which is in agreement with t he experiment.