Polyamide amino acids of high molecular weight were prepared by the self‐polycondensation of aromatic diaminodicarboxylic acids in polyphosphoric acid. Polyamide amino acids thus obtained were converted to the fully aromatic polymer containing benzoxazinone rings by the cyclodehydration in polyphosphoric acid. The resulting aromatic polymer shows excellent thermal stability up to 450°C in nitrogen. The fully aromatic heterocyclic polymers were characterized by good thermal stability and the molecular weight attained was high enough to exhibit film‐forming properties for the products.
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Masaru Kurihara (1967) studied this question.