Cyclopolycondensations. IV. Investigation of the polymerization mechanism of aromatic diaminodicarboxylic acid in polyphosphoric acid and the thermal stability of aromatic polyamide amino acids

In order to elucidate the reaction mechanism of the polyphosphoric acid solution Polymerzation of aromatic diaminodicarboxylic acid, a model reaction with anthranilic acid in Polyphosphoric acid was studied. It was established that the polymerization procceds via the formation of phosphorylated reaction intermediates followed by self‐polycondensation to form high molecular weight aromatic polyamides containing benzoxazinone rings along the polymer main chain. The effect of additives such as benzidine and naphthalene was studied, and the mechanism of polymerization is discussed based on the elementary analyses and on infrared spectral and proton magnetic resonance spectral data. Furthermore, the thermal stability of aromatic polyamides was determined by thermogravimetric and differential thermal analyses, and the crystallinity of the polymer was measured by X‐ray diffraction.