THEORY FOR THE SOLUBILITY OF GASES IN POLYMERS - APPLICATION TO MONATOMIC SOLUTES

The polymer reference interaction site model (PRISM theory) is applied to the problem of calculating the solubility of monatomic gases in am orphous polyethylene. One can consider this system as an approximation to the solubility of gases in ethylene/propylene elastomers. The chem ical potential of a solute atom in the polymer is decomposed into two distinct contributions: a positive athermal contribution calculated by growing the solute atom from a point particle and a negative attracti ve contribution computed from first-order perturbation theory using th e athermal system as the reference state. Good agreement is found betw een the PRISM calculations and available experimental data on solubili ty of gases in common elastomers with no adjustable parameters. Furthe rmore, PRISM theory is successful in predicting several interesting tr ends observed experimentally: (1) solubility increases with the size o f the solute atom, (2) solubility is a monotonically increasing functi on of the critical temperature of the solute species, and (3) the temp erature coefficient of solubility crosses over from positive to negati ve for solutes having critical temperatures of approximately 65 K.