DIFFUSION OF GASES IN POLYMER BLENDS NEAR THE LOWER CRITICAL SOLUTIONTEMPERATURE

Gas diffusion through miscible blends of polystyrene (PS) with poly(vi nyl methyl ether) (PVME) and poly(styrene-stat-acrylonitrile) (PSAN) w ith poly(methyl methacrylate) (PMMA) is studied from temperatures belo w the corresponding lower critical solution temperature (LCST) to temp eratures above. The Arrhenius equation describes the temperature depen dence of diffusion coefficients of pure components. Diffusion coeffici ents of methane in the 20/80 PS/PVME blend also follow the Arrhenius e quation in the temperature ranges above and below their corresponding LCST; however, discontinuity is observed in the LCST region. In contra st to the PS/PVME blend, discontinuity in the LCST region is not obvio us for nitrogen and methane in the 50/50 PSAN/PMMA blend. These phenom ena are discussed in terms of free volume and morphology changes in th e LCST region.