Thermally rearranged (TR) poly(benzoxazole-co-amide) membranes for hydrogen separation derived from 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB), 4,4′-oxydianiline (ODA) and isophthaloyl chloride (IPCl)

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• The solubility of polymers was enhanced by inducing flexible ether group.
• Thermal analysis of TR-PBOAs verified the two step thermal cyclization reaction.
• H2 permeability increased with temperature due to high activation energy.

Thermally rearranged poly(benzoxazole-co-amide) (TR-PBOA) copolymer membranes were prepared by treating poly(o-hydroxyamide-co-amide) (PHAA) precursors by in-situ thermal cyclization reaction for the H2 separation at high temperature. The physical properties, membrane processability and gas permeation property can be controlled by varying the ratio of diamine compounds. The rigid biphenyl moiety in the copolymer membranes increases gas selectivity whereas the flexible ether moiety improves membrane processability as well as gas permeability. Moreover, thermal rearrangement process affects the gas separation properties of TR copolymer membranes. TR polymer membranes derived from polyhydroxyamides (PHAs) demonstrated high H2 permeability, but low H2/CO2 selectivity. However, TR-PBOA copolymer membranes improved H2/CO2 selectivity. Both permeability and selectivity of H2 over CO2 increased due to the high activation energy for H2 permeation through the copolymer membranes and can be explained by thermodynamic theory with temperature. The highest performance was 26.8 Barrer of H2 permeability and 8.0 of H2/CO2 selectivity measured at 210 °C.