A Highly Reactive Benzoxazine Monomer, 1-(2-hydroxyethyl)-1,3-Benzoxazine: Activation of Benzoxazine by Neighboring Group Participation of Hydroxyl Group

N-(2-Hydroxyethyl)-1,3-benzoxazine (1a) underwent the polymerization much faster than other N-alkylbenzoxazines. The origin of this high reactivity would be the "neighboring group participation" of hydroxyl group, i.e., intramolecular reaction of hydroxyl group with cationic moieties of the zwitterionic intermediates formed by the ring-opening reaction of benzoxazine, affording a 5-membered cyclic N, O-acetal 4. 1a and 4 were in equilibrium through the zwitterionic intermediates, and this equilibrium, increased the probability of presence of the intermediates in the system to promote the polymerization. The present concept of the "acceleration of the polymerization of benzoxazine by neighboring group participation of nucleophilic moiety" would contribute to effective molecular designs of highly reactive benzoxazine monomers.© 2010 American Chemical Society.