Abstract: Novel compositions which are highly stable and resistant to degradation by ultraviolet (UV) light are prepared by dispersing polysubstituted 1,5-diazacycloalkanes in the material subject to degradation, particularly in polyolefins. The cyclic compounds of this invention have (a) a fixed three-carbon bridge between the N.sup.1 and N.sup.5 atoms of the diaza ring, the remaining portion of the ring having a variable length bridge of two or more carbon atoms, (b) an N-adjacent carbon atom of the diaza ring is polysubstituted, that is, has two substituents which may be cyclizable. Monocyclic 1,5-diazacycloalkanes are prepared by reducing the corresponding 2-keto-1,5-diazacycloalkane with metal hydride; bicyclic 1,5-diazacycloalkanes, particularly fused ring bicyclic compounds such as substituted 1,5-decahydrobenzodiazepines are prepared by reaction of a diaminocycloalkane with an unsaturated ketone or acid and reducing with metal hydride.