The study of diffusion and permeation of methane, nitrogen, and helium in miscible blends of poly(styrene-stat-acrylonitrile) (PSAN) and poly(methy1 methacrylate) (PMMA) at 35-140°C shows that permeation coefficients (P) of helium followed the linear logarithmic mixing rule. Positive deviations from the linear logarithmic mixing rule were observed for permeation and diffusion coefficients (0) of methane and nitrogen below the glass transition temperature (Tg). The deviations decreased with increasing temperature and disappeared above Tr The experimental results were analyzed by free volume and activated state theories. The Arrhenius plots of log D or log P us. the reciprocal of temperature exhibited discontinuities in the glass transition region for all gases and blend compositions. The discontinuities are caused by large thermal expansion coefficient differences between the rubbery and glassy states of PSAN and PMMA. The sorption of methane in 50150 PSAN/ PMMA has dual-mode characteristics below Tr Experimental Studies MaterialsPoly(styrene-stat-acrylonitrile) (PSAN), containing 30 wt. 070 of acrylonitrile and poly(methy1 methacrylate) (PMMA) were obtained from Scientific Polymer Products. The weightaverage molecular weight of PSAN is 185,000 as supplied by the manufacturer. The weight-average molecular weight of PMMA is 93,000 and the number-average molecular weight 46,000.The glass transition temperatures ( T,) of the polymers were measured by the use of a Perkin Elmer 7 Series differential scanning calorimeter (DSC). DSC experiments were carried

Gas diffusion through miscible blends of polystyrene (PS) with poly(viny1 methylether