Stabilizing polyolefins with diacyl dihydrazides

A process for stabilizing homo- or copolymeric polyolefins, characterised by incorporating into said material from 0.01 to 5 percent by weight, calculated on the material to be stabilized, of a compound of the formula ##STR34## wherein R and R' independently of each other represent an aralkyl group which is substituted in its aryl moiety by one or two alkyl groups having each from 1 to 4 carbon atoms and a hydroxyl group or a phenyl group which is substituted by one or two alkyl groups having each from 1 to 4 carbon atoms and a hydroxyl group and X represents the direct bond, an alkylene radical having from 2 to 8 carbon atoms, a phenylene radical or a naphthylene radical, and n represents 0 or 1.