Novel imide-aryl ether phenylquinoxaline copolymers were prepared and their morphology and thermal properties investigated. A key feature of these copolymers is the incorporation of an aryl ether phenylquinoxaline linkage into a semi-rigid polyimide backbone based in pyromellitic dianhydride (PMDA) with 4,4’-oxydianiline (ODA) and either 2,3-bis-[(3-aminophenoxy)phenyl]quinoxaline or 2,3-bis[(4-aminophenoxy)phenyl]quinoxaline as co-diamines. These monomers were prepared by a novel nucleophilic aromatic substitution reaction of 2,3-bis(4-fluorophenyl)quinoxaline with 4- or 3-aminophenol in the presence of K2CO3 These diamines were used as co-monomers with PMDA and ODA to synthesize poly(amic-acids) which were cast and cured (350 degrees C) to effect imidization, affording tough films. The copolymers with high phenylquinoxaline compositions displayed glass transition temperature values in the 300 degrees C range. The thermal stability of the copolymers was comparable to that of the parent polyimide, with decomposition temperatures between 455 and 480 degrees C. The morphology of the copolymers was investigated by dynamic mechanical thermal analysis and wide angle X-ray diffraction.