Heterocyclic compounds of the formula (I) ##STR1## where n is an integer from 1 to 70,R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each independently of the others hydrogen, C.sub.1 -C.sub.22 -alkyl or C.sub.5 - or C.sub.6 -cycloalkyl orR.sup.1 and R.sup.2 and also R.sup.3 and R.sup.4 are each pairwise trimethylene or tetramethylene,A is a direct bond, C.sub.1 - C.sub.22 -alkylene, cycloalkylene, ##STR2## where m and o are each from 1 to 20 andR.sup.6 is C.sub.1 -C.sub.22 -alkyl, C.sub.5 -C.sub.12 -cycloalkyl, C.sub.7 -C.sub.18 -phenylalkyl, unsubstituted or substituted phenyl or C.sub.2 -C.sub.22 -cyanoalkyl,M is a group of the formula ##STR3## which may be bonded to A not only via the nitrogen but also via the carbon, and whereR.sup.7, R.sup.8, and R.sup.10 are each independently of the others C.sub.1 -C.sub.4 -alkyl orR.sup.7 and R.sup.8 and/or R.sup.9 and R.sup.10 are each pairwise tetramethylene or pentamethylene andR.sup.11 is hydrogen or C.sub.1 -C.sub.4 -alkyl,B is a direct bond, C.sub.1 -C.sub.22 - alkylene, C.sub.7 -C.sub.16 -phenylalkylene or carbonyl-, carboxamido- or carboxylato-interrupted C.sub.3 -C.sub.22 -alkylene andR.sup.5 is hydrogen, cyano, hydroxyl, ##STR4## R.sup.12 is hydrogen, C.sub.1 -C.sub.22 -alkyl, C.sub.5 -C.sub.12 -cycloalkyl, C.sub.7 -C.sub.16 -phenylalkyl, unsubstituted or substituted phenyl or 5- or 6- membered heterocyclyl or, when n is 1, M--B--R.sup.5 is a group of the formula ##STR5## R.sup.13 is C.sub.1 -C.sub.4 -alkyl, R.sup.14 is hydrogen, C.sub.1 -C.sub.4 -alkyl or C.sub.1 -C.sub.4 -alkoxy andR.sup.15 is C.sub.1 -C.sub.12 -alkyl, have very good stabilizing properties, no self-color, good compatibility with polymers, a low vapor pressure and stability to thermal decomposition.