Unique self-catalyzed cationic ring-opening polymerization of a high performance deoxybenzoin-based 1,3-benzoxazine monomer

Abstract

An asymmetric bis(1,3-benzoxazine) monomer based on deoxybenzoin has been synthesized through Mannich condensation. The chemical structure of this deoxybenzoin-based monomer has been confirmed using 1H NMR, 13C NMR, FT-IR and elemental analysis. The assignments for the oxazine protons and carbon atoms in the asymmetric structure have also been confirmed using two-dimensional (2D) NMR techniques, including 1H-1H nuclear Overhauser effect spectroscopy (NOESY) and 1H-13C heteronuclear multiple quantum coherence spectroscopy (HMQC). In addition, the effect of incorporation of deoxybenzoin on the mode of polymerization of benzoxazine has been investigated using differential scanning calorimetry (DSC), in situ FT-IR and 1H NMR spectroscopy. This deoxybenzoin containing bis(benzoxazine) exhibits a low polymerization temperature resulting from a unique self-catalyzed cationic polymerization mechanism. Furthermore, the thermal stability of the resulting polybenzoxazine has been studied using thermogravimetric analysis (TGA). This deoxybenzoin-based polybenzoxazine exhibits high thermal stability and low flammability, with a Td5 temperature of 403 °C, a high char yield value (68%) and low total heat release (THR of 11.4 kJ/g).