Ultraviolet absorbers and related materials

When a molecule (A) absorbs a quantum of light it is activated to an electronically excited state A, after which a number of process may occur. These may be summarised as follows  

Reactions (d) and (e) occur much less frequently than reactions (a)-(c) but do so at a sufficient rate to cause changes in most polymers. There are three methods available for combating such effects light screens, ultraviolet absorbers and quenching agents. 

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Triazoles, such as phenylbenzotriazole, naphthylbenzotriazole, and related compounds, such as benzophenone are UV absorbers. A particularly well-known group of ultraviolet stabilizers are hydroxyphenylbenzo-triazole-based compounds. However, UV light stabilizers of this type are often lost from the product into which they are incorporated by leaching or hy evaporation. To overcome these difficulties, efforts have been directed towards chemically incorporating the ultraviolet light stabilizer into the polymeric backbone of the material to be protected. ... 

Another factor to consider relates to the type of cure and the effect this may have on the substrate. The use of an ultraviolet (UV) curing adhesive on opaque materials is not going to be satisfactory as UV energy from the UV source can be absorbed or blocked preventing the adhesive to cure at the joint. Good examples being many types of thermoplastics such as polycarbonate (PC), polystyrene (PC), acrylic, acrylonitrile-butadiene-styrene (ABS), etc. 

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