TRANSPORT OF GASES IN MISCIBLE POLYMER BLENDS ABOVE AND BELOW THE GLASS-TRANSITION REGION

The study of diffusion and permeation of methane, nitrogen, and helium in miscible blends of poly(styrene-stat-acrylonitrile) (PSAN) and pol y(methyl methacrYlate) (PMMA) at 35-140-degrees-C shows that permeatio n coefficients (P) of helium followed the linear logarithmic mixing ru le. Positive deviations from the linear logarithmic mixing rule were o bserved for permeation and diffusion coefficients (D) of methane and n itrogen below the glass transition temperature (T(g)). The deviations decreased with increasing temperature and disappeared above T(g)). The experimental results were analyzed by free volume and activated state theories. The Arrhenius plots of log D or log P vs. the reciprocal of temperature exhibited discontinuities in the glass transition region for all gases and blend compositions. The discontinuities are caused b y large thermal expansion coefficient differences between the rubbery and glassy states of PSAN and PMMA. The sorption of methane in 50150 P SAN/PMMA has dual-mode characteristics below T(g).