Four polyimides and one polypyrrolone derived from 2,2’-bis(p-trimellitoxyphenyl) propane dianhydride were synthesized and the transport properties of H-2, O-2 and N-2 in these polymers were measured at 30 degrees C and 1 atm (1.01 x 10(5) Pa). Values of permeability and permselectivity were significantly affected by diffusivity and diffusivity selectivity, respectively. The polypyrrolone shows simultaneously increased permeability and permselectivity over the analogous polyimides. The introduction of a methyl group into the backbone of polyimide results in an increase in permeability and permselectivity. Replacement of the rigid moiety in polyimide with a more flexible segment leads to increased permeability but decreased permselectivity.