Mechanistic Pathways for the Polymerization of Methylol-Functional Benzoxazine Monomers

The polymerization mechanism of methylol-functional benzoxazine monomers is reported using a series of monofunctional benzoxazine monomers synthesized via a condensation reaction of ortho -, meta -, or para -methylol–phenol, aniline, and paraformaldehyde following the traditional route of benzoxazine synthesis. A phenol/aniline-type monofunctional benzoxazine monomer has been synthesized as a control. The structures of the synthesized monomers have been confirmed by 1 H NMR and FT-IR. The polymerization behavior of methylol monomers is studied by DSC and shows an exothermic peak associated with condensation reaction of methylol groups and ring-opening polymerization of benzoxazine at a lower temperature range than the control monomer. The presence of methylol group accelerates the ring-opening polymerization to give the ascending order of para-, meta -, and ortho -positions in comparison to the unfunctionalized monomer. Furthermore, rheological measurements show that the position of methylol group relative to benzoxazine structure plays a significant role in accelerating the polymerization.