A STUDY OF THE PHOTODECOMPOSITION PRODUCTS OF AN ACYLPHOSPHINE OXIDE AND 2,2-DIMETHOXY-2-PHENYLACETOPHENONE

The photodecomposition of 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 2,2-dimethoxy-2-phenylacetophenone was investigated under normal ultraviolet curing conditions. The rate of formation and the identity of the many photodecomposition products produced by each photoinitiator were similar, whether amines (triethylamine or N-methyldiethanolamine) were present or not. Experimental evidence indicates that the role of amines is predominantly one of oxygen scavenger. It was also established that the shelf-life (stability) of the photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide is short when present in an epoxydiacrylate/N-methyldiethanolamine ultraviolet curable formulation. The decomposition products identified indicated that this is due to the occurrence of transesterification and hydrolysis reactions.