Hindered amines nitroxyl radical precursors

The early recognition of the role of stable nitroxyl free radicals, e.g., 2,2,6,6-tetramethyl-4-oxopiperidine, and their hindered amine precursors, in polymer stabilization soon led to the development of the hindered amine light stabilizer (HALS) class of photoantioxidants. The first HALS, Tinuvin 770, AO-33, (commercialized in 1974) proved to offer much higher UV-stabil-ity to polymers than any conventional UV-stabilizer available at the time such as UV-absorbers, nickel compounds and benzoates. Table 3). 

This chapter is a comprehensive overview of the progress in the field of generation, chemistry, and application of nitroxyl radicals and their precursors, for example, hindered amines of the 2,2,6,6-tetramethy1-piperidine series. Because of the importance of nitroxyl radicals to polymer stabilization, this application is discussed at length, while the others are touched upon briefly. 

Another important field of the application of nitroxyl radicals and their precursors, hindered amines, is the protection of polymers and other organic compounds against the factors causing their thermo- and photo-destruction. In the present work, an attempt has been made to describe briefly the main achievements in this field. 

The possibility of stabilizing polymers with hindered nitroxyl radicals is based on their reaction with polymer radicals which are engaged in propagating polymer oxidation. It was established that hindered amines, the precursors of nitroxyl radicals, are also effective photostabilizers and, as such, they are more effective than most of the common photostabilizers for polymers. 

These results suggest that hindered amine compounds could be converted to stable nitroxyl radicals through the corresponding amino radicals in polymers that is, they are the precursors of the stable radicals. In fact a key compound, 2,2,6,6-tetramethyl-4-oxopiperi-dine (42), showed high light-stabilizing activity in polypropylene, comparable to that of the nitroxyl radicals, lending support to this interpretation. 

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See also in sourсe #XX -- [ , ]

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