Sorption and diffusion of hydrocarbon vapors in glassy polymers

Abstract

Abstract Sorption isotherms in the region of low relative pressures have been determined at several temperatures for methane, propane, and chlorodifluoromethane in polystyrene and for propane in bisphenol‐A polycarbonate and poly(vinylacetate). The results are well represented by the isotherm equation of Dual Sorption Theory as applied to glassy polymers. The temperature dependence of the isotherm parameters is examined and discussed; the Langmuir component to sorption decreases as the glass transition temperature is approached and measurements with poly(vinylacetate) confirm that this component is absent above the transition. Average diffusion coefficients were obtained from sorption (desorption) rate curves at constant pressure for propane in polystyrene and polycarbonate and a procedure developed for their analysis to yield the diffusion coefficients of the two sorbed species of penetrant. For the polycarbonate there is evidence of mobility in that fraction of the penetrant: population exhibiting Langmuir‐type sorption.