Miscibility in Terpolymer--Copolymer Blends

The phase behaviour of 50/50 blends of a series of terpolymers from styrene, maleic anhydride, and acrylonitrile with styrene--acrylonitrile copolymers and styrene--maleic anhydride copolymers has been determined using the single glass transition temperature criterion. The appropriate expression for the overall blend interaction energy density according to the extended Flory--Huggins theory is examined and the general shapes of miscibility contours in composition space are deduced and presented in a novel manner. The experimental miscibility is dependent on both terpolymer and copolymer composition, and is well described by this expression using values of segmental interaction parameters available from the literature.