Hindered amine light stabilizer hydroperoxides

The stabilizers chosen for evaluation include different types of heat and light stabilizers selected to represent different mechanisms of action as well as chemical compositions (ArJi). Types of stabilizers evaluated include benzotriazole and benzophenone light stabilizers [ultraviolet (UV) light absorbers], hindered amine light stabilizers (HALS, catalytic radical scavengers), hindered phenol heat stabilizers (antioxidant radical scavengers), and thioester heat stabilizers (antioxidant hydroperoxide decomposers). 

S. Mizokawa and Y. Ohkatsu, Influence of ultraviolet absorbers on decomposition of hydroperoxide by hindered amine light stabilizers, J. Jpn. Petrol. Inst. 2007, 50, 1-7. 

Primary phenohcs (free-radical scavengers) or secondary phosphite (hydroperoxide decomposer) may be used as heat stabilizers for WPC, while light stabilizers commonly used in WPC include UV absorbers (e.g., benzotriazole or benzophenone), radical scavengers or hydroperoxide decomposers, and hindered amine light stabilizers (HALS). 

Hindered amine light stabilizers have attracted enormous scientific and commercial interest due to their efficiency as photo-antioxidants. The stabilization process in the presence of HALS involves the interference of secondary >NH or tertiary (>NCH3) groups with hydroperoxides POOH generated by oxidation chain mechanism of polymer alkyl radicals P. HALS-derived nitroxides >NO, formed through scavenging peroxyls POO by hydroxylamine species >NOH, are the key intermediates in the HALS stabilization mechanism because they are able to quench alkyl radicals arising in the initiation step of oxidation [100, 101]. The involvement of HALS in the stabilization process can be attributed to their ability to remain an... 

Hindered amine stabilizers are transparent to visible and terrestrial UV light (300-400 nm). In polymeric matrices, they are oxidized in a sacrificial reaction by way of a not yet fully understood mechanism to stable nitroxyl (aminoxyl) radicals >N-0. A mechanism based on the reaction of HASs with alkyl hydroperoxides and alkyl peroxyl radicals is presented in Scheme 9.14 [87]. 

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