Role of phenolic derivatives in photopolymerization of an acrylate coating

The photopolymerization of acrylate resins on wood surfaces suffers from retardation and inhibition effects due to the phenolic derivatives present at the interface. This article details the study of the effect of a set of phenolic compounds on the initiation step. The global effect was recorded by differential scanning calorimetry and photocalorimetry. A comparison between a direct photocleavable initiator such as 2,2-dimethyloxy-2-phenylacetophenone (DMPA) and a two-component system like benzophenone/N-methyldiethanolamine (BP/MDEA) suggests that the retardation effect observed in the latter case is due to the interaction between phenols and the triplet state of BP. Subsequently, nanosecond transient absorption (NTA) spectroscopy was used to measure in acetonitrile the quenching rate constants k Q . A hydrogen abstraction occurred, and the ketyl radical quantum yield was also determined by NTA experiments. In comparison with the photoreduction mechanisms proposed in the literature, the high k Q values obtained were tentatively correlated to the half-wave oxidation potentials of phenols in order to discuss the involvement of an electron transfer within the reaction. Some EPR experiments were done to confirm in situ the photoreduction process at the wood surface and the creation of phenoxyl radicals. The interaction of phenols with some initiating radicals was also studied.