Synthesis and Ring-Opening Polymerization of Mono-Benzoxazines Based on 2-(2-Hydroxyethoxy)phenol and Aniline/Furfurylamine.

Two mono-benzoxazines are synthesized from 2-(2-hydroxyethoxy)phenol, aniline, furfurylamine, and formaldehyde, respectively. The ring-opening polymerization (ROP) of the two mono-benzoxazines is studied with differential scanning calorimetry, Fourier transform infrared spectroscopy, nuclear magnetic resonance, and electrospray ionization mass spectrometry. Compared to phenol-aniline-based benzoxazine, both 2-hydroxyethoxy and N-furfuryl groups can reduce the ROP temperature. Side reactions related to the 2-hydroxyethoxy and N-furfuryl groups are involved in the ROP. The ring-opening reaction leads to the formation of zwitterion intermediates, which undergo chain propagation to form oligomeric zwitterions and series of cyclic and linear oligomers in the early stage of ROP, indicating that the same benzoxazine monomer can polymerize into different polymers through different ROP pathways. Based on the experimental results, the ROP pathways are proposed and validated by density functional theory calculations.