N-Isopropylmorpholine (IPM) was used as a model to investigate the properties of the morpholino substituent present in 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one (1). It was shown by real time IR (RTIR) spectroscopy, photocalorimetry, bulk polymerization studies and the curing of thin films that IPM acts as a physical quencher for the triplet state of 1 and that it is a very poor hydrogen donor. Thus any interaction of the ground state of 1 with its triplet state is likely to lead to physical quenching, thereby reducing the initiating efficiency of 1. Evidence is also presented that the use of high concentrations of N-methyldiethanolamine can lead to reduction of the triplet state of 1, thereby enhancing the initiating efficiency of 1. It was confirmed that thioxanthones can sensitize the alpha cleavage of 1.