7-hydroxynadic acid: A new end cap for improved oxidation resistance in addition polyimides

We consider possible replacements for the norbornenyl end cap in addition p olyimides that should favor bridge degradation and lead to lower weight los s in the resin system. Our preliminary evaluation demonstrates that molding powder made with 7-hydroxynorbornene-2,3-dicarboxylic acid, 17, as the end cap can be fully imidized at 200 degreesC. By differential scanning calori metry (DSC), onset of cross-linking occurs approximately 50 degreesC lower than that for the unsubstituted end cap. The hydroxy-bearing carbon on 17 i s more easily oxidized to carbonyl on aging in the polymer than the parent end cap. Therefore, the new end cap more highly favors bridge degradation. However, processing studies, long-term weight loss, and careful evaluation of degradation mechanisms must be carried out to fully assess 17 as a more thermo-oxidatively stable replacement for the parent norbornenyl end cap.