Gas sorption and characterization of thermally rearranged polyimides based on 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)

▸ Solubility of H2, N2, O2, CH4, and CO2 increases as thermal rearrangement proceeds. ▸ Non-equilibrium free volume increases during thermal rearrangement. ▸ Solubility scales with critical temperature of the penetrant gas.