Photochemistry of novel water-soluble parasubstituted benzophenone photoinitiators: A photocalorimetric and photoreduction study

Abstract

The photopolymerization quantum yields of five novel water-soluble para-substituted benzophenone derivatives were determined in a water-soluble monoacrylate resin using N, N′-dimethylaniline as a co-synergist and these are compared with their corresponding photoreduction quantum yields in water in the presence of 2- N, N-diethylethanolamine. A linear correlation is found between the two sets of data, confirming that the photopolymerization activity of these photoinitiators is associated with photoreduction of the excited carbonyl triplet state with the amine. Cationic structures were found to be less active than the anionic structures and this is reflected by a corresponding marked difference in their triplet lifetimes. One of the photoinitiators, 4-methylsulphonium benzophenone sodium salt, exhibited a photoreduction quantum yield of 1.5 under the experimental conditions used. This is associated with secondary processes due to the reaction of alkylamino radicals with a ground state ketone molecule.