Hindered amine light stabilizer formation

D.K. Hodgeman, Formation of polymer-bonded nitroxyl radicals in the UV stabilization of polypropylene by a bifunctional hindered amine light stabilizer, J. Polym. Sci. Polym. Chem. Ed. 1981, 19, 807. 

Hindered amine Light stabilizers Hindered amine scavenges radictils which are produced by light. This effect may be expltiined by the formation of nitroxyl radictils... 

It is known that the lone pair electrons of amines are capable of capturing a carbon radical long enough to convert it to a nonradical species, as is the case with hindered amine light stabilizers (HALS) [70], It stands to reason that species with available lone pairs (Lewis bases) stabilize the TFE biradicaloid, allowing the end opposite to the catalyst to exist as a full radical and subsequently react. Barabanov s [23] observation of polymer formation is evidence for this terminal radical. Other perfluorinated species capable of forming biradicaloids would undergo similar radical stabilization. 

Light stabilizers are divided into three categories UV absorbers, free radical terminators, and quenchers (2). The UV absorbers will absorb the UV radiation to prevent the formation of free radicals. Hindered-amine light stabilizers (HALS) terminate the free radicals. They are more expensive than UV absorbers. The third category of light stabilizers are quenchers that are often represented by nickel complexes. Because of toxicity of heavy metals and substances of concern (SOCs) specification from OEMs and government regulations, quenchers are not as widely used. 

The material considered here allows us to understand the influence of sterically hindered amines, which act as stabilizers against the light-induced degradation of polyolefines. The sterically hindered amines easily undergo oxidation after cation-radical formation ... 

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