Synthesis and ring-opening polymerization of 2-substituted 1,3-benzoxazine: the first observation of the polymerization of oxazine ring-substituted benzoxazines

2-Substituted 1,3-benzoxazines (two benzoxazine monomers used in this paper are abbreviated as PH-a-[2]ba and PH-pda-[2]ba) having a phenyl group as an oxazine ring substituent are synthesized with benzaldehyde through 2-hydroxy-N-phenylbenzylamine structures. The polymerization of these monomers is observed for the first time and confirmed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR). The poly(PH-a-[2]ba) derived from 2-substituted 1,3-benzoxazines exhibits good thermal properties based on TGA analysis, despite showing slight inferiority to poly(PH-a), an unsubstituted counterpart of PH-a-[2]ba. Additionally, benzylideneaniline is extracted during the polymerization, indicating that this compound is the byproduct of the polymerization mechanism. Structural verification is achieved by synthesizing benzylideneaniline and comparing its 1H-NMR spectrum with the reaction byproduct.