Structural evolution and reaction pathways in ring-opening polymerization for mono-benzoxazines based on phenol–aniline/cyclohexylamine†

Abstract

Here, we provide an insight into the molecular structure of products formed in the early stage of ring-opening polymerization (ROP) for phenol–aniline/cyclohexylamine-based mono-benzoxazines. By use of a combination of the experimental data obtained from Fourier transform infrared spectroscopy, nuclear magnetic resonance, and electrospray ionization mass spectrometry with density functional theory calculations, the ROP pathways of the mono-benzoxazines are proposed and validated by experiment. The initial polymerization products of the two mono-benzoxazines consist of a range of fragment species and a series of cyclic and linear oligomers, and these products are formed via zwitterionic intermediates. It could be predicted that polybenzoxazines with higher molecular weight would be generated through electrophilic aromatic substitution of hydrogen on the active benzene rings of the oligomers in the later stage of the ROP.