Comparison of mixed and pure gas permeation characteristics for CO 2 and CH 4 in copolymers and blends containing methyl methacrylate units

Abstract

Permeation of pure CO 2 and CH 4 and their 50 50 mixtures (at 5 and 20 atm partial pressures) were measured at 35°C in a series of styrene/methyl methacrylate copolymers, SMMA, and a series of miscible blends of bischloral polycarbonate, BCPC, and poly(methyl methacrylate), PMMA. PMMA is significantly plasticized by CO 2 at 20 atm; whereas, BCPC and, to a lesser extent, polystyrene are not. Thus, by incorporating MMA units into the copolymer or in the blend, a varying extent of plasticization response was built in. Mixed gas separation factors were found to be well-predicted by pure gas measurements for CO 2 and CH 4 at 5 atm partial pressure for all copolymers and all blends. However, at 20 atm partial pressure of CO 2, the actual mixed gas separation factors are much lower than that predicted by pure gas measurement as the MMA content of the copolymers or the blends increased. Significant history or conditioning effects accompany plasticization in glassy polymers so the results obtained depend on the measurement protocol. For this reason, no attempt was made to fit these data to current models since they do not allow for this fact.