Role of the Medium on the Reactivity of Cleavable Photoinitiators in Photopolymerization Reactions

Abstract

The efficiency of 11 cleavable photoinitiators in polymerization reactions was determined in various media, such as oligomer, acrylate, and methacrylate monomers in solution or in poly(methyl methacrylate). It was found that the efficiency of the photoinitiator strongly depends on the polymerized medium. The results are explained and discussed on the basis of the viscosity effect on the rate constants of the processes involved, resulting in good efficiency/reactivity relationships. Quantum yields of initiation were calculated for an acrylate photopolymerization in solution. The efficiency in viscous bulk media is quite well reflected in the dissociation quantum yields of the photoinitiators measured in solution. The role of the other low-viscosity media is also explained. Kinetic treatments were used to examine the influence of the monomer structure on the propagation and termination rate constants of the reaction. These results allowed to shed some light on the influence of the medium on the initiation efficiency and to provide a better knowledge of the key parameters for practical applications.