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-dimeth-ylamino -40-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 experimen ts carried out in the presence of 2-ethoxythioxanth one (Pila 124), 2 , an additive commonly used in combination w ith 1 as sensitizer, it is inferred that 2 mainly acts via hydrogen abstraction from 1 .