Volumetric Properties and Sorption Behavior of Perfluoropolymers with Dioxolane Pendant Rings

Lattice fluid theory is used to develop transport property-structure correlations for glassy perfluoropolymers with dioxolane pendant rings, a new class of membrane materials for gas separation. Poly(perfluoro-2-methylene-1,3-dioxolane) (poly(PFMD)) and poly(perfluoro-2-methylene-4-methyl-1,3-dioxolane) (poly(PFMMD)) exhibit lower permeability but much higher selectivity than commercial fluoropolymers, such as Teflons AF. Their enhanced separation performance is due to the combined effect of solubility- and diffusivity-selectivity. Moreover, poly(PFMD) and poly(PFMMD) exhibit enhanced CO₂-philicity as compared to Teflons AF, which can be ascribed to the higher oxygen/carbon ratio exhibited by the former materials. To provide rational guidelines to maximize the solubility-selectivity, the enthalpic and entropic contributions to sorption coefficient were calculated and compared for several polymers of practical interest for gas separation. In the absence of localized penetrant-polymer interactions, gas sorption is controlled essentially by the free volume and solubility-selectivity is controlled by the polymer cohesive energy density.