Further EPR-spin trapping studies of the photoinitiating activity of Irgacure 369

The radicals formed upon visible light irradiation of the photoinitiator 2-benzyl-2-dimethylamino-4′-morpholinobutyrophenone (Irgacure 369), 1, were investigated by means of EPR spectroscopy coupled with the spin trapping technique both in the absence and in the presence of a monomer. The results suggest a dual behavior of 1 that may act both as a Type I and a Type II photoinitiator. From experiments carried out in the presence of 2-ethoxythioxanthone (Pila 124), 2, an additive commonly used in combination with 1 as sensitizer, it is inferred that 2 mainly acts via hydrogen abstraction from 1.