Layered and Cellular Morphologies in Atactic/Syndiotactic Polystyrene Blends

Abstract

This paper demonstrates for the first time that by blending a polymer with its isomer and subsequently conditioning the mixture with CO₂ gas a layered and cellular morphology can be obtained. Previous reports in the literature on generating layered and cellular morphologies use a stacking method forcing layers of polymers together followed by foaming the material. In this study we present single-phase blends of atactic polystyrene (PS) with its isomer syndiotactic polystyrene (sPS) and their fluid phase behavior with CO₂. Equilibrium solubility and diffusion coefficients of the gas in the PS/sPS blends in the ratios 75/25, 50/50 and 25/75 wt% was determined at 0 and 35 °C; and the role of CO₂ solubility on the types of morphologies generated was investigated. With a decrease in temperature and hence an increase in gas solubility as well as changes in blend composition, foams with various morphological characteristics were obtained. In particular the 50/50 wt% PS/sPS blend conditioned with CO₂ at 0 °C and 3.4 MPa resulted in an intriguing morphology with alternating layers containing small and large cells within a given layer respectively.