Synthesis and chemical degradation of thermostable polyamide with imine bond for chemical recycling

The mono-, di-, and triamino-substituted cyclic phenylazomethine (CPA) and diamino-substituted linear phenylazomethine (OPA) were synthesized in one-step via dehydration of aromatic amine and ketone in the presence of titanium tetrachloride. The linear and branched aromatic polyamides were prepared by the direct polycondensation of the di- or triamine monomers and various dicarboxylic acids in the presence of triphenyl phosphite and pyridine as condensation agents. Thermogravimetric analysis (TGA) revealed that the polymers had a high thermal stability. The temperature for a 10% weight loss determined by TGA was over 500 degrees C for some of the polymers. The hydrolysis property of the polymers was investigated using UV-vis spectroscopy. The spectra of the polymer solution in the presence of dilute sulfuric acid revealed that a simple and selective acid-catalyzed hydrolysis of azomethine bonds quantitatively occurred in mild conditions without cleavage of the amide bond, and more than 99% of the azomethine bonds were hydrated in less than 10 min at ambient temperature. The hydrolysis rate of the polymer was also determined. In polymer materials, these aromatic polyamides made it possible to relate high thermal stability with the decomposition property for effective chemical recycling.