Gas transport properties of thermally rearranged (TR) polybenzoxazole –silica hybrid membranes

Abstract

Novel thermally rearranged polybenzoxazole (TR-PBO) -based silica hybrid membranes were prepared via thermal rearrangement and sol – gel processes, and their gas transport properties were investigated. The pristine TR-PBOs rearranged at different temperatures showed higher fractional free volume (FFV) and d-spacing values than the poly(ortho-hydroxy imide) as a precursor polymer. Gas permeability of TR-PBO – silica hybrids increased with increasing silica content. The increased gas permeability was mainly attributed to increased gas diffusivity, suggesting the formation of free volume holes at polymer/silica interfacial region. The TR-PBO – silica hybrids possessed an outstanding CO2/CH4 selectivity, exceeding the upper bound trade-off line for CO2/CH4 separation. The notable CO2/CH4 selectivity was achieved by synergistic effects of (1) enlarged FFV and d-spacing by the thermal rearrangement towards PBO and (2) the additional formation of characteristic free volume holes with a size-selective CO2/CH4 separation ability at polymer/silica interfacial region by the hybridization with silica.