PERMEATION AND PLASTICIZATION BEHAVIOR OF GLASSY-POLYMERS - A WAXD INTERPRETATION

Wide angle X-ray diffraction (WAXD) has been used to investigate the mechanism of plasticization in various glassy polymers. Polymer films were exposed to either CO2, N2 or n-hexane and the change in the average intersegmental spacing was measured by WAXD. The results have been used to rationalize various types of CO2 permeability versus pressure profiles in glassy polymers reported in the literature. The increase in CO2 permeability with pressure in the case of cellulose acetate (CA) and poly (methyl methacrylate) (PMMA) arises from the significant increase in the intersegmental spacing on exposure to high pressure CO2. Smaller changes in intersegmental spacing are seen in the case of polycarbonate and various polysulfones. The change in the intersegmental spacing can be correlated with the T(g) of the polymer prior to plasticization and also with the penetrant solubility in the polymer. The "conditioning" effect of CO2 in the case of phenolphthalein based polysulfone has been attributed to changes in the segmental mobility, while the intersegmental chain spacing remains unchanged.