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

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 CO 2 /CH 4 selectivity, exceeding the upper bound trade-off line for CO 2 /CH 4 separation. The notable CO 2 /CH 4 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 CO 2 /CH 4 separation ability at polymer/silica interfacial region by the hybridization with silica. Image 1 • Novel TR-PBO – silica hybrid membranes for gas separation were prepared. • The TR-PBO – silica hybrids possess high gas permeability and CO 2 /CH 4 selectivity. • The CO 2 /CH 4 selectivity is enhanced with increasing silica content. • Free volumes created at polymer/silica interfaces contribute to CO 2 /CH 4 separation. [ABSTRACT FROM AUTHOR]