Stabilizer combination

A compound of the formula ##STR24## wherein R.sub.1 and R.sub.1 ' independently of one another are each linear or branched C.sub.1 -C.sub.18 alkyl, C.sub.3 -C.sub.8 cycloalkyl, C.sub.3 -C.sub.6 alkenyl or C.sub.7 -C.sub.12 aralkyl,

• R.sub.4 and R.sub.5 independently of one another are each hydrogen, unsubstituted or halo-, cyano-, hydroxyl-, amino-, C.sub.1 -C.sub.4 alkoxycarbonyl-, carbamoyl-, N-mono- or N,N-di-C.sub.1 -C.sub.4 alkyl carbamoyl-, glycidyl or phenyl-substituted, linear or branched C.sub.1 -C.sub.12 alkyl, or linear or branched C.sub.4 -C.sub.28 alkyl, which is interrupted by one or more N, S or O atoms and which is unsubstituted or substituted by hydroxyl or by a radical --OR.sub.6 or are a radical --CO--R.sub.6 or --SO.sub.2 --R.sub.6, and R.sub.6 is C.sub.1 -C.sub.12 alkyl, unsubstituted or C.sub.1 -C.sub.4 alkyl-substituted phenyl or C.sub.7 -C.sub.12 aralkyl.