Processable polyimides with high glass transition temperature and high storage modulus retention at 400 degrees C

End-capped polyimide precursor solutions in ethyl alcohol were prepared by incorporating carbonyl groups into the polymer backbone of a second-generat ion PMR (in situ polymerization of monomer reactants) polyimide, PMR-II-50, which exhibited good features as a matrix resin for carbon-fibre-reinforce d composites. Cured polyimides were prepared in an analogous process as the PMR-II polyimides. The thermal and thermo-oxidative stability of the cured polyimides was systemically investigated. It was found that the cured poly imide containing a 1:1 mole ratio of the carbonyl group [-C(O)-] to the hex afluoroisopropyl group [-C(CF3)(2)-] in the polymer backbone possessed a ve ry high glass transition temperature (440 degreesC) and an excellent therma l decomposition temperature (576 degreesC). The onset temperature of the st orage modulus curve was measured at about 400 degreesC with-high retention (> 55%) of the storage modulus at 400 degreesC, compared to 10-15% of the c orresponding PMR-II polyimide. Carbon-fibre-reinforced composites also show ed a high onset temperature of the storage modulus (420 degreesC) and high storage modulus retention (> 85%) at 400 degreesC. Preliminary results indi cated that the composite laminate exhibited excellent mechanical strength r etention at 371 degreesC, which was superior to that of CF/PMR-II composite s.