DIFFUSION AND SORPTION IN ETHYLENE-PROPYLENE COPOLYMERS - COMPARISON OF EXPERIMENTAL METHODS

The solubility and diffusion coefficients of various solvents in ethyl ene-propylene copolymers with different ethylene contents were measure d over a temperature range of 30-200 degrees C using capillary column inverse gas chromatography and gravimetric sorption. The value of the Flory-Huggins parameter decreased with an increase in temperature. The infinitely dilute diffusion coefficients obtained by the two methods were consistent with each other. The data indicate that the diffusion coefficients and solubility parameters are independent of the ethylene content of the copolymers. The results obtained from the sorption tec hnique were extrapolated using a free-volume theory to the limit of ze ro solvent concentration, and the free-volume model was used to interp ret the diffusion data. Analysis of the diffusion data indicated that the inclusion of an activation energy in the free-volume model does no t significantly improve the correlation of the diffusion data.