Two and three component photoinitiating systems based on coumarin derivatives

This study shows that several coumarin or ketocoumarin/additives combinations (bisimidazole derivative, mercaptobenzoxazole, titanocene, oxime ester) are able to initiate quite efficiently a radical polymerization reaction. The interactions between the excited states of coumarins or a ketocoumarin and various additives have also been studied by laser absorption spectroscopy, time resolved fluorescence and photoconductivity; the redox potentials of these different compounds have been measured and allowed the calculation of free enthalpy variations for a possible electron transfer reaction. The whole results explain the interaction mechanism and show that the coumarins are able to form radicals through an electron transfer reaction with the different additives whereas the ketocoumarin leads to an energy transfer with bisimidazole and to an hydrogen abstraction with the benzoxazole derivative. (C) 2001 Elsevier Science Ltd. All rights reserved.