Synthesis and gas transport properties of hyperbranched polybenzoxazole - silica hybrid membranes

•Gas transport properties of hyperbranched PBO - silica hybrids were investigated.•The hybrids showed high gas permeability and CO2/CH4 selectivity.•The CO2/CH4 selectivity was improved by hybridization with silica.•The improved CO2/CH4 selectivity was caused by increased free volume holes.

Gas transport properties of hyperbranched polybenzoxazole (PBO) - silica hybrid membranes were investigated. The hyperbranched PBO - silica hybrid membranes were prepared via in-situ silylation method and sol-gel reaction. Thermal decomposition temperature of the hybrid membranes increased with increasing silica content, indicating improved thermal stability brought by the hybridization with silica. The hyperbranched PBO - silica hybrid membranes showed higher gas permeability than corresponding linear-type PBO - silica hybrid membranes with similar chemical structure. It was worth noting that both CO2 permeability and CO2/CH4 selectivity of the hyperbranched PBO - silica hybrid membranes were increased with increasing silica content across the upper bound trade-off line for CO2/CH4 separation. The prominent CO2/CH4 separation ability of the hyperbranched PBO - silica hybrid membranes might be achieved by large amounts of free volume holes, that were fundamentally brought by a characteristic hyperbranched structure and additionally crated around polymer/silica interfacial area, equipped with unique distribution and interconnectivity advantageous for a size-selective CO2/CH4 separation.

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