Comprehensive Study of the Synergistic Effect in Photocyclic Three-Component Initiating System for Radical Polymerization

In radical photopolymerization, synergistic three-component initiating systems lead to far better radical polymerization performances compared with the corresponding two-component systems. The third component is able to produce additional initiating radicals, regenerate the photoinitiator, thus forming a photocyclic initiating system, and consume terminating photoproducts that occur in two-component photoinitiators. However, the respective roles of these reactions are not well-defined. Kinetic modeling is applied to a synergistic photocyclic initiating system to provide insights into the synergistic effects observed in a system based on an organic dye (Rose Bengal), a triazine derivative, and a tertiary amine as the third component. From kinetic modeling, the low polymerization performances of the dye-triazine system are attributed to back electron transfer but mainly to termination reactions by the oxidized dye photoproduct. Introduction of the amine greatly improves the polymerization performances. From time-resolved experiments, this is explained by its reaction with oxidized Rose Bengal to regenerate the dye and produce additional initiating radicals. It is also shown that the combination of these three components leads to dual photocyclic behavior. Kinetic modeling of the three-component system shows good agreement with the experimental data. Finally, a theoretical study using the kinetic model developed here highlights that the consumption of the oxidized dye terminating agent by the tertiary amine is the main reason for the improved polymerization kinetics.