Photoinitiated free radical polymerization using benzoxazines as hydrogen donors

Free radical polymerization of methyl methacrylate (MMA) is initiated upon irradiation at λ > 350 nm in CH₂Cl₂ that contains benzoxazine (P-a) and one of the following photosensitizers: benzophenone (BP), thioxanthone (TX), 2-chlorothioxanthone (CTX), 2-isopropyl thioxanthone (ITX), and camphorquinone (CQ). The postulated mechanism is based on the intermolecular reaction of the excited photosensitizer with the tertiary amino moiety of the ground state P-a and a subsequent hydrogen abstraction reaction. The resulting aminoalkyl radicals initiate the poly-merization. The incorporation of P-a groups into polymers is demonstrated by spectroscopic methods. The possibility of deep curing using the described photoinitiating system followed by the thermal ring opening of the incorporated P-a groups is also demonstrated.