All-aromatic biphenylene end-capped polyquinoline and polyimide matrix resins

Biphenylene end-capped polyquinoline and polyimide resins afford low void content graphite-reinforced composites with good initial properties. However, with both resins, rapid degradation occurs during oxidative isothermal aging at elevated temperatures. The degradation is not observed during isothermal aging under a nitrogen atmosphere which suggests that the biphenylene end-cap (or the resulting crosslink/chain extension structures) is not particularly thermooxidatively stable. The nature of the thermooxidative instability is currently under investigation.