Photoinitiated Free Radical Polymerization Using Benzoxazines as Hydrogen Donors

Abstract

AbstractSummary: 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 polymerization. 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.Schematic of the photoinitiated free radical polymerization using benzoxazines as hydrogen donors.magnified imageSchematic of the photoinitiated free radical polymerization using benzoxazines as hydrogen donors.