Photo-initiator systems for the polymerization of acrylates, based on a mixture of an aryl ketone and an ~,co-diaminoalkane, have been investigated. Rate constants for the photoreduction of fluorenone by ct,co-diaminoalkanes have been evaluated; it was found that CH3N groups are more relative than CHaCH2N groups. The relative rates of photo-oxidation of ct,co-diaminalkanes sensitised by benzopbenone have been determined. Surprisingly, little correlation exists between the susceptibility of an amine towards oxidation and its ability to reduce excited carbonyl groups. Several mixtures composed of an aryl ketone and an ~t,to-diaminoalkane were found to initiate the polymerization of methyl methacrylate. The efficiency of initiation appears to be related to the efficiency of reaction of the triplet carbonyl compound with the amine. The efficiency of a particular combination of an aryl ketone and an amine to cure films of acrylate oligomers is also governed to some extent by the efficiency of reaction of the triplet carbonyl compound with the amine. However, the structure of the amino alkyl radical produced in the initiation reaction appears to be of greater importance in determining the efficiency of polymerization. Radicals of the type R2NCHCH2OR were found to be highly efficient.