Abstract
Polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS)-ionic liquid (IL) block-graft copolymer was synthesized via a three-step process, including chloromethylation, quaternization, and anion exchange. The SEBS-IL block-graft copolymer exhibited good compatibility with the IL, affording defect-free SEBS-IL/IL membranes. The IL domain had a good affinity for specific gas molecules such as CO2 to allow selective gas solubility. In addition, the SEBS-IL/IL membranes exhibited a well-defined microphase-separated structure to achieve efficient transport pathways for the gas molecules. Consequently, a significant improvement in gas separation performance (permeability and selectivity) approaching the Robeson upper bound limit was achieved. In particular, the SEBS-IL/IL 50% membrane showed an H2 permeability of 90.8 Barrer and CO2 permeability of 134 Barrer with CO2/N2 selectivity of 26, CO2/CH4 selectivity of 10.6, H2/N2 selectivity of 17.6, and H2/CH4 selectivity of 7.2. These gas permeation parameters were 2–3 times higher than those of pristine SEBS membrane. The presented SEBS-IL/IL membrane approach provides important insights to rationally design a microphase-separated polymer structure based on high compatibility with IL monomer for efficient gas separations.
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