Mab. Meador et al., 7-hydroxynadic acid: A new end cap for improved oxidation resistance in addition polyimides, CHEM MATER, 13(8), 2001, pp. 2649-2655
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.