Pure gas permeability coefficients of CH4, N-2, O-2, CO2, and H-2 are reported for thermally rearranged (TR) polymers derived from polyimides based on 3,3'-dihydroxy-4,4'-diamino-biphenyl and 2,2'-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (HAB-6FDA). These HAB-6FDA polymers were prepared with hydroxyl, acetate, propanoate, and pivalate groups in the ortho-position to the imide ring. Polymers with acetate ortho-position groups were synthesized via either thermal or chemical imidization. Pure gas permeability was approximately five Limes higher after rearrangement at 450 degrees C in TR polymers from polyimides with acetate, propanoate, and pivalate ortho-position groups relative to TR polymers prepared from polyimides with hydroxyl of-am-position groups, in samples with non hydroxyl ortho-position groups, those with larger ortho-position groups had higher gas permeability for TR conversions less than roughly 60%, but permeability increased to similar values as conversion exceeded 60%. In all samples, the CO2/CH4 selectivity also approached a similar value as TR conversion increased. Despite their higher permeability, fractional free volume was not significantly higher in TR polymers from polyimides bearing non-hydroxyl ortho-position groups than in samples with hydroxyl ortho-position groups. Therefore, average free volume alone cannot explain this behavior, suggesting that free volume distribution is likely affected by these groups. (C) 2014 Elsevier B.V. All rights reserved.