Abstract: The invention relates to photopolymerizable compositions comprising (a) a prepolymer containing photopolymerizable olefinic double bonds, (b) photoinitiator of the formula ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are as defined in claim 1, and optionally (c) an ester of acrylic or methacrylic acid or an allyl ether or allyl ester of a polyol.Owing to their excellent light sensitivity, these compositions are suitable for the economic production of high temperature resistant protective layers and relief structures having excellent resolution and good contours.