Investigation of the structural features and polymerization mechanism of a novel bio-based benzoxazine using different lewis acids

Abstract Benzoxazines are heterocyclic compounds known for their high thermal stability, flame retardancy, and excellent mechanical performance, making them promising candidates for high-performance polymer applications. This study aimed to synthesize a benzoxazine monomer (Ca-c) derived from cardanol (Ca), the main component of cashew nut shell liquid (CNSL), using hexamethylenetetramine (HMTA) as a source of both methylene and nitrogen units, and to evaluate the influence of Lewis acids (AlCl 3 , FeCl 3 , MgCl 2 , and ZnCl 2 ) on the polymerization process. The monomer was synthesized from cardanol and HMTA, producing a resin that was employed without further purification. Formulations were prepared by incorporating metal salts at 7.5% (mol/mol), followed by curing under a controlled heating protocol. This approach enabled evaluation of the influence of the salts on the curing behavior and properties of the benzoxazine system. Characterization by FTIR and NMR ( 1 H and 13 C) confirmed the formation of the oxazine ring. DSC analyses revealed a significant reduction in the onset polymerization temperature, especially with MgCl 2 (up to 29 °C). TGA showed good thermal stability, and diffuse reflectance spectroscopy indicated metal–ligand interactions, particularly in the Zn 2+ -containing systems. The results demonstrate that metal salts act as effective catalysts, enabling efficient polymerization under milder conditions.