Novel polybenzoxazinones with tricyclic fused‐rings

A series of polybenzoxazinones containing phenoxathiin and phenoxaphosphine units were prepared from tricyclic diacid chlorides and 4,4′‐diaminobiphenyl‐3,3′‐dicarboxylic acid and 4,4′‐diamino‐3,3′‐diphenylmethane dicarboxylic acid. The low temperature solution polymerization technique afforded polyamic acid which subsequently underwent cyclization along the polymer chain in a solvent mixture of refluxing N,N′‐dimethylacetamide, acetic anhydride, and pyridine to give polybenzoxazinones in moderate yields. The polymers thus obtained had inherent viscosities in the range of 0.15–0.23 dL/g, were sparingly soluble in N‐methyl‐2‐pyrrolidone, and were found to be thermally more stable than the corresponding open‐chain polymer with diphenylether linkage.