MODEL STUDIES ON THE MECHANISM OF HALS STABILIZATION

Hindered Amine Light Stabilizers (HALS) are know to inhibit the photo- oxidation of polymers. A key reaction in their stabilization mechanism is believed to be the conversion of a hindered aminoether into a nitr oxyl radical. Several different possible mechanisms for this conversio n were explored. One, the elimination of the aminoether to form an ole fin and hydroxylamine (an intermediate in the formation of a nitroxyl) , while possible at high temperatures, cannot account for the inhibito ry activity we observed for secondary and primary aminoethers. Direct radical displacement by peroxy radicals was also considered. However, the products predicted by this reaction pathway were not observed. Fin ally, oxidation of the nitrogen by a peroxy radical, by either electro n transfer or a radical attack on the nitrogen, was investigated. Whil e electron transfer was shown to be unlikely, direct oxidation of the aminoether nitrogen was supported by our results. A detailed mechanism for the reaction of both alkyl- and acyl-peroxy radicals with aminoet hers is proposed.