High-temperature thermoset polyimide resins were prepared using p-phenylenediamine and a 1:3 mixture of 1,1,1,3,3,3-hexafluoro-2,2-bis(3,4-dicarboxyphenyl)propane dianhydride (6FDA) and 3,3’,4,4’-tetra-carboxybiphenyl dianhydride (BPDA) for the imide backbone, and diarylacetylene derivatives as reactive capping agents. The thermo-oxidative stability at 370-degrees-C of the cured resins was evaluated in comparison with control samples based on several known reactive capping agents. The polyimide resin end-capped with 4-(phenylethynyl)phthalic anhydride exhibited the best thermo-oxidative stability.