Ethylenically unsaturated compounds of the general formula I ##STR1## where R.sub.1 is alkyl of 1 to 4 carbon atoms, cyclopropyl, cyclopentyl, cyclohexyl, phenyl or phenyl in which some or all of the hydrogen atoms have been replaced by radicals R.sup.4, not more than two substituents R.sup.4 being identical, or R.sup.1 together with R.sup.2 or together with R.sup.6 forms a --CH.sub.2 --CH.sub.2 -- or --CH.sub.2 --CH.sub.2 --CH.sub.2 -- bridge,R.sup.4 is alkyl of 1 to 24 carbon atoms, --OH, --O--R.sup.7, --S--R.sup.7, ##STR2## R.sup.2 or R.sup.6, independently of one another, both are hydrogen, or one of the radicals R.sup.4, or, where R.sup.1 is aryl,R.sup.2 or R.sup.6 is a direct bond to R.sup.1 in the ortho-position with respect to the carbonyl group, andR.sup.3 and R.sup.5 are each hydrogen, one of the radicals R.sup.4 or a group the general formula II ##STR3## where R.sup.7 and R.sup.8 are each alkyl of 1 to 4 carbon atoms,R.sup.9 is cycloalkyl of 5 or 6 carbon atoms,R.sup.10 is hydrogen or alkyl of 1 to 4 carbon atoms andR.sup.11 is hydrogen or alkyl of 1 to 4 carbon atoms,with the proviso that either R.sup.3 or R.sup.5 is a group of the general formula II,are suitable for the preparation of polymers which, after exposure to actinic radiation, have increased internal strength.