Study on the Ring-Opening Polymerization of Benzoxazine through Multisubstituted Polybenzoxazine Precursors

To discuss the mechanism of ring-opening polymerization (ROP) of benzoxazine, a bisphenol A/diaminodiphenylmethane-based polybenzoxazine precursor (PBz-0M), o-dimethylbisphenol A/diaminodiphenylmethane-based polybenzoxazine precursor (PBz-2M), and o-dimethylbisphenol A/o-tetramethyldiaminodiphenylmethane-based polybenzoxazine precursor (PBz-6M) were prepared. Among the polybenzoxazine precursors, free ortho positions to the O of oxazine are available for PBz-0M. No free ortho or para position to the O of oxazine is available for PBz-2M, but free ortho position to the N of oxazine is available. No free ortho positions to the O or N of oxazine are available for PBz-6M. According to DSC, IR, and thermal analysis, we found that the ROP of PBz-2M can be carried out even though no free ortho or para position to the O of oxazine is available. We conclude that the ROP is carried out through the ortho position to the N of oxazine and propose a reaction mechanism to explain the polymerization.