Hindered amine stabilizers weathered coatings

HALS are capable of stabilization of polyolefins, especially polypropylene, against outdoor weathering for periods very much longer than can be achieved by any other stabilizer. They have found widespread application as stabilizers for polyolefins and for many surface coatings. They do not absorb in the UV and have little intrinsic radical trapping ability, so that the mechanism of their action was initially somewhat mysterious and has been extensively reviewed (Allen, 1981 Klemchuk, 1985). It is still somewhat contentious in detail, but is accepted to involve an initial oxidation of the parent hindered amine to the corresponding nitroxide. 

The number of studies in this area is limited, but a few have shown exposure of coatings to atmospheric contaminants to be detrimental. Sampers [35] reports that, in a study of polyolefin samples exposed both in Florida and on the Mediterranean coast of France, a dramatic difference was seen in polymer lifetime. Samples exposed on the Mediterranean had only half the life of those in Florida. The two stations had broadly similar weathering parameters the differences should have led to longer lifetimes in France. Sampers concluded that constituents in the rain or wind had chemically interacted with the hindered amine light stabilizers in the polymers exposed in France, causing these samples to be especially vulnerable to UV degradation. 

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