Dependence of ultraviolet absorbers' performance on ultraviolet wavelength

So far, ultraviolet absorbers (UVA) have been discussed mainly on the basis of the extinction coefficient (ɛ), and the light degradation of polymeric materials is explained by photolysis of hydroperoxides and Norrish reactions of ketones. This study focuses on the photo-antioxidant ability as characteristic which UVA must possess for the light stabilization, and examines the dependence of the photo-initiation by oxidation products on UV wavelength range. As a result, it has been made clear that UV rays ranging 290-320 nm trigger photo-oxidation (degradation) by photolysis of hydroperoxides and Norrish reactions of ketones, and α-diketone derived from further oxidation of the ketones, for example, initiates photo-oxidation at a surprisingly higher velocity under UV rays above 350 nm. UV rays in the range of 320-350 nm participate in the photo-initiation by an enone (CCCO) structure in addition to the above-mentioned oxidation products, in which the initiation velocity is the medium between the velocities for the above two wavelength ranges. That is to say, the longer the UV rays wavelength range, the faster the photo-initiation velocity. Finally, it is concluded that excellent UVA are judged based on λmax rather than ɛ, and that UVA absorbing longer wavelength UV rays can more control the photo-oxidation.