Typical bimolecular photoinitiators (PIs) for radical polymerization of acrylates show only poor photoreactivity because of the unwanted effect of back electron transfer Therefore a PI system consisting of benzaldoxime esters and 4 methyl benzophenone was investigated by photo differential scanning calorimetry experiments Surprisingly reactivities are comparable to that of classical monomolecular Type I PIs like Darocur 1173 probably because of an energy transfer from the triplet state of the benzophenone based sensitizer to the oxime ester initiator Furthermore sufficient thermal stability was pro yen by TGA and storage stability experiments of a resin formulation under elevated temperature (C) 2010 Wiley Periodicals Inc J Polym Sci Part A Polym Chem 48 5865-5871 2010