MISCIBILITY OF STYRENE-MALEIC ANHYDRIDE AND STYRENE-ACRYLONITRILE BLENDS STUDIED BY POSITRON-ANNIHILATION LIFETIME SPECTROSCOPY

Blends of melt-mixed styrene-maleic anhydride and styrene-acryilonitri le copolymers were examined with respect to miscibility and free volum e parameters. Differential scanning calorimetry, dynamic mechanical an alysis, Scanning electron microscopy, and positron annihilation lifeti me spectroscopy were used to judge blend miscibility, It was found tha t blends containing copolymers with similar amounts of styrene were mi scible, Positron annihilation lifetime spectra of all blends were eval uated with the POSITRONFIT and the MELT program, where the latter can be used to obtain lifetime distributions. The mean o-Ps lifetimes (or hole sizes) of the blends were found always to be between those of the pure constituents. Pronounced negative deviations of the o-Ps intensi ty-from weighted averages were measured in miscible blends but not in immiscible ones. Immiscible blends exhibit, on the basis of MELT evalu ations, unsymmetric and broader o-Ps lifetime distributions than do mi scible blends.