EFFECT OF VARIOUS EXPOSURE HISTORIES ON SORPTION AND DILATION IN A FAMILY OF POLYCARBONATES

Methane sorption and dilation isotherms along with their dependence on sample exposure history are presented for three systematically varied polycarbonates. Sorption and dilation levels of CH4 in the various polycarbonates are shown to be increased by two methods of exposure to CO2 termed “conventional conditioning” and “exchange conditioning”. The exchange-conditioning procedure produces the largest increases for all three polycarbonate samples. The largest percentage changes in properties are noted for the well-packed unsubstituted bisphenol-A polycarbonate (PC), which displays a 44% increase in sorption and a corresponding 58% increase in dilation with the conventional-conditioning protocols. This polymer also showed the largest changes in properties for the exchange-conditioning procedure, with a 79% increase in sorption and a corresponding 167% increase in dilation over unconditioned values. Qualitatively, the substituted materials, with less efficiently packed matrices and higher Tg values, showed smaller increases under both conditioning protocols as compared to standard PC, indicating a trend of smaller sorption and dilation enhancements for samples that experience smaller increases in fractional free volume as induced by the conditioning treatments. © 1990, American Chemical Society. All rights reserved.