Isomer Effects on Gas Transport Properties of Polybenzoxazole-Silica Hybrid Membranes

Gas transport properties of novel polybenzoxazole(PBO) - silica hybrid membranes with a para-substituted structure were investigated. The para-substituted PBO - silica hybrid membranes were prepared with a para-substituted poly(o-hydroxy amide)as a precursor polymer and tetraethoxysilane(TEOS) via thermal oxazolization and sol-gel processes. The neat para-substituted PBO membranes treated at different temperatures showed higher fractional free volumes than corresponding PBO membranes with a meta-substituted structure reported previously. Gas permeability of the para-substituted PBO - silica hybrid membranes increased with increasing treated temperature and silica content. The increased permeability was brought by increased inter-molecular chain distance and free volume holes formed at the polymer / silica interfaces. It was worth noting that the hybrid membranes showed simultaneous enhancements of CO2 permeability and CO2/CH4 selectivity, suggesting improved size-selective CO2/CH4 separation ability by the free volume holes formed at the polymer / silica interfaces. It was concluded the para-substituted PBO - silica hybrid membranes possessed prominent gas permeability and selectivity, and were expected to apply to highperformance gas separation membranes.