Diffusion of oxygen and carbon dioxide in thermally crystallized syndiotactic polystyrene

The diffusion, solubility, and permeability behavior of oxygen and carbon d ioxide were studied in amorphous and semicrystalline syndiotactic polystyre ne (s-PS). The crystallinity was induced in s-PS by crystallization from th e melt and cold crystallization. Crystalline s-PS exhibited very different gas permeation behavior depending on the crystallization conditions. The be havior was attributed to the formation of different isomorphic crystalline forms in the solid-state structure of this polymer. The P crystalline form was virtually impermeable for the transport of oxygen and carbon dioxide. I n contrast, the a crystalline form was highly permeable for the transport o f oxygen and carbon dioxide. High gas permeability of the a crystals was at tributed to the loose crystalline structure of this crystalline form contai ning nanochannels oriented parallel to the polymer chain direction. A model describing the diffusion and permeability of gas molecules in the composit e permeation medium, consisting of the amorphous matrix and the dispersed c rystalline phase with nanochannels, was proposed. Cold crystallization of s -PS led to the formation of a complex ordered phase and resulted in complex permeation behavior. (C) 2001 John Wiley & Sons, Inc.