Examples are N,N'-(??-aminopropyl)-5,5-dimethyl-hydantoin or -benzimidazolone, and those of the formula ##STR6## in which Rb is alkylene with 1 to 12, preferably 1 to 4, C atoms or ##STR7## in which Rc is a hydrogen atom or methyl and a is an integer from 1 to 20.