A rigid polypyrrolone material that exhibits excellent thermal and chemical stability has been studied to determine its potential for novel applications in membrane-based ps separations at elevated temperatures. Operation at high temperatures produces favorably high membrane productivities; however, losses in permselectivity usually occur as well. Gas transport and sorption measurements have been obtained for this polypyrrolone at temperatures up to 200-degrees-C. The loss of permselectivity with increasing temperature that occurs for most gas pairs is discussed in terms of both solubility and diffusivity selectivity. The temperature dependences of productivities and permselectivities for various ps pairs are also compared to those of other materials thought to be attractive for high temperature gas separations. In most cases, the structurally rigid polypyrrolone out performs these other materials, demonstrating favorable productivities and permselectivities over the entire range of temperatures studied.