A THERMODYNAMIC ANALYSIS OF GAS SORPTION-DESORPTION HYSTERESIS IN GLASSY-POLYMERS

Sorption-desorption isotherms for carbon dioxide in polycarbonate, tetramethylpolycarbonate, hexafluoropolycarbonate, and poly(vinyl benzoate) were fitted using the glassy polymer lattice sorption model (GPLSM). The model requires sorptive dilation data to account properly for lattice compressibility. Using polymer segment-segment interaction energies from the sorption isotherms, the desorption isotherms were fitted with only a single adjustable parameter, the Henry's law constant. Differences in Henry's law constants between sorption and desorption were explained in terms of the unoccupied volume before and after the sorption-desorption process and the ''volatility'' of the gas in the local polymer environment at infinite dilution.