Several families of hydrocarbon polymers (polysulfones, polycarbonates, cellulose acetates, polyamides, and polyimides) have been established as common industrial gas separation membranes over the past three decades. Fluoropolymer membranes have found commercial use because of their unique gas separation properties in addition to their extraordinary chemical resistance and thermo-oxidative stability. To date, studies of gas transport in fluoropolymers have been limited largely to variants of the commercially available perfluoropolymers: Teflon® AF, Cytop™, and Hyflon® AD. Here, we describe gas transport in composite membranes fabricated from copolymers of perfluoro(2-methylene-4,5-dimethyl-1,3-dioxolane) (PFMDD) and chlorotrifluoroethlyene (CTFE). This poly(PFMDD-co-CTFE)-based membranes have far superior gas separation performance compared to the commercial perfluoropolymers for a number of gas pairs, including H2/CH4, He/CH4, and CO2/CH4. The gas separation performance of the membranes depends strongly on the copolymer composition. Increasing the amount of CTFE up to 30 mol% in the copolymer increases the membrane selectivity and reduces permeance. The membranes based on 70 mol% PFMDD-30 mol% CTFE poly(PFMDD-co-CTFE) show H2/CH4 and He/CH4 selectivities of 210 and 480, respectively, values that far exceed those possible with the known commercial perfluoropolymers.
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