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 adapted to obtain the equation of state and Helmholtz free energy for random copolymer systems and random copolymer/homopolymer blends. Miscibility behavior of the blend of poly(styrene-co-p-bromostyrene)/polystyrene is investigated to test the validity of the theory. With the molecular parameters extracted from the experimental PVT data, not only a satisfactory description of the experimental PVT surfaces is obtained, but also the upper critical miscibility behavior of the blend is predicted, which is in agreement with the experiment.