CARBON-DIOXIDE CONDITIONING EFFECTS ON SORPTION AND VOLUME DILATION BEHAVIOR FOR BISPHENOL-A-POLYCARBONATE

Sorption/desorption and volume dilation/consolidation measurements are reported for Bisphenol A-polycarbonate in the presence of carbon dioxide pressures up to 900 psia at 35 °C. Second-exposure sorption and desorption isotherms are presented after conditioning samples at 300,600, and 900 psia. The sorption and volume-dilation data are used to calculate the partial specific volumes of the polymer and penetrant as functions of sorption level. Qualitative physical arguments concerning the nature of the conditioning effect are presented based on this thermodynamic analysis of the gas-glassy polymer system. A fugacity-based dual-mode sorption model is shown to be very useful for describing the sorption and volume- dilation results. The increase in solubility observed during the desorption hysteresis cycle does not appear to be due to the simple introduction of additional packing defects responsible for the Langmuirlike sorption in the as-received sample. Specifically, more subtle and generalized intersegmental, residual dilation appears to be responsible for the enhanced sorption during the desorption process. After total removal of the sorbed gas, however, evidence of a small amount of additional packing defects can be detected with subsequent resorption. This small conditioning effect is shown to be reversed by annealing the polycarbonate sample at 135 °C. © 1990, American Chemical Society. All rights reserved.