Gas permselectivity of hyperbranched polybenzoxazole – silica hybrid membranes treated at different thermal protocols

Abstract

Hyperbranched polybenzoxazole (HBPBO) – silica hybrids were treated at different thermal protocols and their gas permselectivity were studied. Inter-chain distance and free volume of pristine HBPBO were enlarged with increasing treated temperature. Gas permeability and diffusivity of the HBPBO were considerably increased with increasing treated temperature, which was resulted from increased fractional free volume due to enlarged inter-chain distance. Gas permeability of the HBPBO was further increased by the hybridization with silica, mainly owing to the increased gas diffusivity. This fact indicated additional free volume holes were formed at the HBPBO matrix – silica interfaces. It was worth noting the HBPBO – silica hybrids had a prominent CO2/CH4 permselectivity which exceeded the upper bound, and the CO2/CH4 permselectivity was enhanced with increasing treated temperature. The notable CO2/CH4 permselectivity of the HBPBO – silica hybrids would be achieved by the synergistic effect of characteristic hyperbranched molecular structure, thermal treatment, and hybridization with silica.