Use of non-selective, high-molecular-weight poly(ethylene oxide) membrane for CO₂ separation by incorporation of comb copolymer

Although ethylene oxide units are often incorporated into polymeric membranes for CO₂ separations, high-molecular-weight poly(ethylene oxide) (high-M_w PEO) cannot be used effectively due to its inferior separation performance, despite its good solubility in mild solvents (e.g. water and alcohols) and commercial availability at low cost. A high-performance, defect-free membrane for CO₂ separations based on high-M_w PEO was prepared by incorporating the crosslinkable poly(glycidyl methacrylate-g-polypropylene glycol)-co-poly(oxyethylene methacrylate) (PGP-POEM) comb copolymer. The CO₂/N₂ and CO₂/CH₄ selectivity of the neat high-M_w PEO membrane was as low as 0.8 and 0.6, respectively, which increased drastically with increasing comb copolymer content, and the thermal and mechanical properties were also improved. The three-dimensionally interweaved network of the comb copolymer occurred within the PEO matrix, which had a considerable effect on the crystalline structure of the membranes. The crystalline morphology of the membranes and the distribution of comb copolymer within the PEO matrix were comprehensively examined according to the comb copolymer content. The comb copolymer effectively suppressed the formation of non-selective defects by filling the interlamellar and interfibrillar regions of the PEO crystallites. The best separation performance was achieved with a comb copolymer loading of 30 wt%, showing a CO₂ permeability of 120.9 barrer with CO₂/N₂ and CO₂/CH₄ selectivity of 44.9 and 14.5, respectively. The tensile strength and elongation at break reached 7.5 MPa and 1490%, respectively. This work presents an avenue for utilizing a low-cost, commercially-available, high-M_w PEO in gas separation applications, providing insight into the crystalline structure and morphology of these membranes.