ortho-Aromatic polyamides by ring-opening polymerization of N-carboxyanhydrides

Abstract

Among major engineering plastics, aromatic polyamides are high-performance materials with high mechanical strength and heat resistance. However, the production of these materials is limited to para- and meta-aromatic polyamides via polycondensation, leading to polymers with low molecular weight and high dispersity. Here, we report the ring-opening polymerization of N-alkylated aromatic 6-membered-ring N-carboxyanhydrides (6-NCA-R) catalyzed by transition-metal Schiff base complexes in the presence of a base. This system allows the facile synthesis of ortho-aromatic polyamides with high molecular weights via chain-growth polymerization. We propose a mechanism on the basis of the results of polymerizations performed under various reaction conditions. In addition, we show the tunability of polymer solubility and thermal properties by varying the length of N-alkyl side chains and perform copolymerization of 6-NCA-R with heterocyclic monomers to prepare heteroatom-containing copolymers. These findings provide a synthetic pathway for functional polyamide materials with tailored properties for various applications.