Poly(amide-imide)s obtained from 3,5-diamino- N -(thiazol-2-yl)-benzamide and dicarboxylic acids containing various amino acid units

Abstract

This study reports a green approach toward the synthesis of novel optically active poly(amide-imide)s (PAI)s bearing thiazole moiety, which was formed by the polycondensation reaction of 3,5-diamino-N-(thiazol-2-yl)benzamide and various diacids containing natural amino acids in molten tetrabutylammonium bromide. Diamine monomer was synthesized by the reduction of 3,5-dinitro-N-(thiazol-2-yl)benzamide in methanol using iron oxide hydroxide as a catalyst. This catalyst can rapidly reduce the sulfur and azo-containing aromatic nitro compounds to the corresponding amines in high yield by employing hydrazine hydrate as a hydrogen donor. Chiral diacid monomers were synthesized in high yield through the reaction of pyromellitic dianhydride and amino acids (l-isoluecine, S-valine, S-methionine, and l-phenylalanine) in acetic acid. The direct polymerization reactions of these monomers provided a series of new optically active PAIs with inherent viscosities in the range of 0.20–0.28 dL g⁻¹. The obtained polymers were characterized by Fourier-transformed infrared spectroscopy, specific rotation measurements, and the representative of them by proton nuclear magnetic resonance and elemental analysis techniques.