Characterization of the imidization of the aromatic polyimide LARC-160

The polyimide resin LARC‐160 was prepared from diethyl‐3,3′,4,4′‐benzophenone tetracarboxylate (BTDE), ethyl‐5‐norbornene‐2,3‐dicarboxylate (NE), and Jeffamine AP‐22. The imidization reactions of NE and BTDE were studied by HPLC, 13C‐NMR, and IR. NE imidizes slowly at 12°C; BTDE imidizes when the resin is heated above 100°C. Both imidization reactions proceed directly to the imide. Neither amic acid is present in significant quantities at any stage of the imidization reactions. The monomer mixture has been stored at 12°C for periods up to 14 months. The effects of resin aging at this temperature on the chemical composition of the resin monomer mixture and the imidized polymer formed on curing were investigated. Aging the resin monomer mixture has the effect of partially advancing the imidization reaction. Aging also results in the formation of slightly higher‐molecular‐weight polyimide chains after curing of the resin at 140 and 180°C. Bisnadimide (BNI) is observed as a major reaction product, regardless of resin age.