The first observation of 3,1-benzoxazine polymerization for developing high performance thermosets

Abstract

1,3-Benzoxazine has long been considered as a unique polymerizable benzoxazine species to prepare high performance polymers. Herein, polymerization of 2H,4H-3,1-benzoxazine is observed for the first time and the thermal properties of the obtained material are studied. A phenolic hydroxyl-containing mono-functional 3,1-benzoxazine monomer has been synthesized. With additional phenol substitution, 3,1-benzoxazine is able to undergo ring-opening polymerization. The reaction kinetics and variation in the molecular structure during polymerization were systematically investigated. Besides, quantum chemistry simulation showed that the C–O and C–N bond strength reduction in the 3,1-oxazine ring induced by adjacent phenol substitution is the critical factor that endows the monomer with polymerization ability. A polymerization mechanism of 3,1-benzoxazine has been proposed. The reported 3,1-benzoxazine monomer has good evaporation resistance even at 200 °C for 2 hours. More importantly, the cured material shows attractive thermal performance, with a glass transition temperature of 217 °C and a decomposition temperature above 400 °C together with a char yield of 54%. This study offers a new way to develop polymerizable benzoxazines with high performance for numerous emerging applications.