Hindered Amine Light Stabilizers: A proposed photo-stabilization mechanism

Hindered amines are known to act as good photo-oxidative stabilizers for polymers, but controversy still surrounds the mechanism whereby this is achieved. The significance of complex formation between hindered amines and hydroperoxide groups in the mechanism is questioned, and the inability of hindered amines, or their nitroxide derivatives, to act as excited state quenchers is demonstrated. A mechanism involving complexation of trace transition metal impurities is proposed to account for the photo-stabilizing ability of these compounds.