Poly(benzoxazole-co-pyrrolone) copolymers in various compositions were prepared from thermal rearrangements from their precursors of polyimides containing both hydroxyl and amino groups. All the copolymers showed higher gas permeabilities than their precursors, as well as higher gas selectivity than polybenzoxazole or polypyrrolone homopolymers. Thermally rearranged copolymerization of stiff and selective pyrrolone and high free volume, high permeable benzoxazole moieties are novel routes to enhance gas selectivity without significant losses in gas permeability. (C) 2010 Published by Elsevier B.V.