PHOTOPOLYMERIZATION AND PHOTOCHEMISTRY OF NOVEL PHOTOINITIATORS BASEDON P-BENZOYLBENZOPHENONE

Six novel derivatives based on the p-benzoylbenzophenone chromophore h ave been examined in terms of their photochemical and photoinitiator p roperties, All the molecules exhibit high extinction coefficients in t he u.v. region together with high photoinitiator activity for the poly merization of methyl methacrylate. The 2-substituted methyl and isopro pyl derivatives exhibited the lowest activity, consistent with lower p hosphorescence quantum yields and ketyl radical formation on microseco nd flash photolysis compared with the corresponding 4-substituted deri vatives. In the case of 2-substitution with an isopropyl group, ketyl radical formation was not quenched by oxygen indicating that a process of intra-molecular hydrogen atom abstraction predominates. This deriv ative was also less effective than benzophenone as a photoinitiator. A nalysis of the photoproducts in 2-propanol confirmed the involvement o f a single step reaction to give a corresponding pinnacol type compoun d.