The present invention includes a polymer formed by the thermal rearrangement of an ortho-functional polyimide synthesized via chemical imidization with permeation properties for gas separation membranes higher than those synthesized via thermal imidization and a method for forming that polymer having tailored transport properties and different chemical resistance. The present invention also includes a polymer formed by the thermal rearrangement of an ortho-functional polyimide in which a portion of the ortho-position functional group is lost during thermal rearrangement to yield a thermally rearranged polymer with higher permeability than would be seen without the ortho-position group. This ortho-position group can be the result of chemical imidization, or the result of a post-imidization modification reaction.
STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with government support under Grant No DE-FG02-02ER15362 awarded by the Department of Energy. The government has certain rights in the invention.