PHOTOINDUCED POLYMERIZATION REACTIONS IN THE PRESENCE OF LIGHT STABILIZERS - REACTIVITY OF THE PHOTOINITIATOR IN SOLUTION AND IN BULK

Excited-state interactions between light stabilizers (LS) and photoinitiators were investigated, for the first time, through time-resolved laser spectroscopy (TRLS), both in solution and in bulk monomer. The lifetimes of the photoinitiator triplet states and the rate constant of the interactions with oxygen, monomers, and amines in a bulk matrix became available. Fairly long-lived triplet states were detected even in the presence of high acrylate concentrations in the highly viscous monomer/oligomer medium. The practical effects of the addition of LS were evaluated in solution and in film photopolymerization experiments. An excellent agreement was found between the expected effect (from TRLS) and the observed practical behavior of the polymerized system, as evaluated by the rate of polymerization (R(p)) or the superficial hardness of the coating: addition of LS leads to a decrease of R(p) in solution but does not affect the curing rate in practical film photopolymerization performed in air.