Living cationic copolymerization of vinyl ethers having oxyethylene side chains (MOEO3VE and MOEO4VE) with vinyl ethers having thermal-crosslinkable groups (VEEM and VEEA) provided the random-like copolymers [poly (MOEO3VE-VEEM), poly (MOEO4VE-VEEM), poly (MOEO3VE-VEEM), and poly (MOEO4VE-VEEM)]. The obtained copolymer compositions were almost the same as those of the feed ratios, and the copolymers with various composition ratios were synthesized ([MOEO3VE or MOEO4VE]/[VEEM or VEEA] = 2:1, 4:1, 6:1, 10:1, and 14:1). All the copolymers are sticky liquid before crosslinking, but the relatively tough porous Teflon film-based composite membranes were obtained by thermal crosslinking via mathacrylate groups or acrylate groups. All the membranes showed high CO2 permselectivity (P-CO2/P-N2 = 40-51) due to the high CO2 solubility selectivity (S-CO2/S-N2 = 44-61). The CO2 permeability increased as the composition ratios of VEEM and VEEA decreased because the gas diffusivity enhanced by the decrement of crosslinking points. Given the same composition ratio, the increased oxyethylene side chain length is beneficial in enhancing CO2 permeability. The effects of crosslinkable groups on gas permeability were not observed. Poly (M0E04VE-VEEM) and poly (M0E04VE-VEEA) showed the excellent performance for CO2 separation (P-CO2 = 440 and 460 barrer, P-CO2/P-N2 = 51). (C) 2017 Elsevier Ltd. All rights reserved.