Abstract: Compounds of the formula I ##STR1## wherein Ar.sup.1 and Ar.sup.2 represent unsubstituted or substituted phenyl, R.sup.1 represents hydrogen, alkyl, alkoxy, hydroxyalkyl, allyl, benzyl or a group --O--R.sup.2 -NR.sup.3 R.sup.4, R.sup.2 represents alkylene and --NR.sup.3 R.sup.4 is an open chain or cyclic organic amino group, are effective initiators for the photopolymerization of unsaturated compounds or for the photocrosslinking of polyolefins. They can be obtained by different methods which are in themselves known, in particular by reaction of the corresponding haloalkyl ethers or haloalkyl ketals with primary or secondary amines.