Photopolymerization of methyl methacrylate initiated by thioxanthone derivatives: photoinitiation mechanism

The photopolymerization of methyl methacrylate initiated by substituted thi oxanthones in the presence of an amine has been investigated. The polymeriz ation rates in acetonitrile were measured at several amine concentrations. The dependence of the polymerization rates with the amine concentration and the photoinitiation efficiency at a given amine concentration are highly d ependent on the ketone structure. The rare constants for the quenching of t hioxanthones excited states by the monomer and the amine were measured by f luorescence and laser hash photolysis, under the polymerization conditions. These data show that the reactivity of the ketone is also highly dependent on the ketone structure. The values of the quenching rate constants show t hat the initiation efficiency is controlled by the competition between the quenching of the excited states by the monomer and also the amine. From the latter a mechanism is proposed to simulate the dependence of the polymeriz ation rates with amine concentration. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.