Benzimidazole‐ and oxadiazole‐modified aromatic polyimides

Three series of aromatic primary diamines were synthesized. The first series of three contained one or two hydrazide groups. The second series of five contained one or two oxadiazole groups. The third series of four contained one or two benzimidazole groups. Reaction of each diamine with either pyromellitic dianhydride or 3,4,3′,4′‐benzophenonetetracarboxylic dianhydride gave a series of soluble polymeric amic acids, from which films of good thermal stability were cast. The heat‐cured films were either oxadiazoleimide or benzimidazole‐imide polymers, depending upon the diamine used. When hydrazide‐amic acid polymers were heated, the conversion of amic acid to imide was essentially complete before any substantial portion of the hydriazide linkages were converted to oxadiazole. The latter conversion was accompanied by degradation. A better method of preparation for these polymers is through the oxadiazole contaning diamines. One hydrazide‐imide polymer was prepared from trimellitic anhydride and was converted to an oxadiazole‐imide by heating. The reaction of equimolar quantities of a dianhydride with 3,5,2′‐triaminobenzanilde gave a soluble polymer which was converted to a benzimidazole‐imide by heating.