A mechanistic investigation of the three-component radical photoinitiator system eosin Y spirit soluble, N-methyldiethanolamine, and diphenyliodoniumchloride

Photo-DSC and in situ, time-resolved, laser-induced, steady-state fluoresce nce spectroscopy were used to study the initiation mechanism of the three-c omponent system: Eosin Y spirit soluble (EYss), N-methyldiethanolamine, and diphenyliodonium chloride. Kinetic studies based on photo-DSC revealed tha t the fastest polymerization occurred when all three components were presen t (the next fastest was with the dye/amine pair, and the slowest was with t he dye/iodonium pair). However, the laser-induced fluorescence experiments showed that the pairwise reaction between the eosin and iodonium bleaches t he dye much more rapidly than does the reaction between the eosin and amine . We concluded that although a direct eosin/amine reaction can produce acti ve radicals in the three-component system, this reaction is largely oversha dowed by the eosin/iodonium reaction, which does not produce active radical s as effectively. We proposed that the amine reduces the oxidized dye radic al formed in the eosin/iodonium reaction back to its original state as well as the simultaneous production of an active initiating amine-based radical . Because of the difference in the pairwise reaction rates for eosin/amine and eosin/iodonium, it is likely that this regeneration reaction was the pr imary source of active radicals in the three-component eosin/amine/iodonium system. (C) 2001 John Wiley & Sons, Inc.