Solubility of light gases in poly(n-butyl methacrylate) at elevated pressures

The solubility of CH4, C2H6, and CO2 in poly(n-butyl methacrylate) (PnBMA, T-g = 20-27 degrees C) was measured at temperatures (T) from -10 to 40 degrees C and at pressures up to 40 atm. The solubility of CH4 in glassy PnBMA is satisfactorily described by the ''dual-mode-sorption'' model. C2H6 and CO2 were found to plasticize PnBMA at pressures higher than a few atmospheres. The solubility of C2H6 and CO2 in glassy PnBMA can be represented over the entire pressure range investigated by a modified dual-mode sorption model that takes into account the effects of plasticization, including the lowering in the glass-transition temperature of the polymer. The present high-pressure solubility measurements are consistent with low-pressure data (< 1 atm) reported earlier. The solubility of CH4, C2H6, and CO2 in PnBMA decreases with increasing temperature. The solubility of CH4 and CO2 in glassy PnBMA is lower than that in glassy poly(ethyl methacrylate) (PEMA, T-g = 57-71 degrees C) which, in turn, is lower than the solubility in glassy poly(methyl methacrylate) (PMMA, T-g = 105-120 degrees C) under comparable conditions. The ''Langmuir capacity'' constant in the dual-mode sorption model, c'(H), for CH4 and CO2 in the above poly(alkyl methacrylates) and many other glassy polymers correlates satisfactorily with (T-g-T). However, this correlation overestimates the values of c'(H) for CO2 in polyimides and other polymers with high glass-transition temperatures.