SORPTION OF SMALL MOLECULES IN VARIOUS POLYCARBONATES AND KAPTON-H

Pressure-composition isotherms were determined at 20 degrees C for CO2 in Kapton and various substituted polycarbonates and for H2O, Ar, N-2 , CH4, and acetone in bisphenol-A-polycarbonate. The isotherms are des cribed by two parameters an average free energy of sorption and a widt h of a Gaussian distribution of free sorption energies. Within the fra mework of a recent model these parameters can be calculated assuming a n elastic distortion of the polymer caused by the incorporation of sol ute atoms in preexisting holes. By comparing experimental values with predictions of the model the experimental width of the free energy dis tribution is only 30% smaller than the theoretical one. Functional rel ationships are obeyed between the sorption parameters on the one hand and glass transition temperature, average hole volume, and molecular v olume of the solute on the other hand. Deviations occur for larger mol ecules like acetone and ethylene which are attributed to a viscoelasti c distortion of the polymer. Comparing free energies of solution for t he rubbery and glassy state of the polymer reveals more negative value s for the glassy polymers despite their extra elastic distortion energ y. This discrepancy is overcome by taking into account that the occupi ed volume has to be re-formed in the case of the rubbery or liquid pol ymer. (C) 1998 John Wiley & Sons, Inc.