Benzophenone-antioxidant combination

Figure 6. Inhibition of discoloration with benzophenone-antioxidant combination—Fade-ometer exposure...

As already shown, it is technically possible to incorporate additive functional groups within the structure of a polymer itself, thus dispensing with easily extractable small-molecular additives. However, the various attempts of incorporation of additive functionalities into the polymer chain, by copolymerisation or free radical initiated grafting, have not yet led to widespread practical use, mainly for economical reasons. Many macromolecular stabiliser-functionalised systems and reactive stabiliser-functionalised monomers have been described (cf. ref. [576]). Examples are bound-in chromophores, e.g. the benzotriazole moiety incorporated into polymers [577,578], but also copolymerisation with special monomers containing an inhibitor structural unit, leading to the incorporation of the antioxidant into the polymer chain. Copolymers of styrene and benzophenone-type UV stabilisers have been described [579]. Chemical combination of an antioxidant with the polymer leads to a high degree of resistance to (oil) extraction. 

Suggestions have also been made that better overall performance can be achieved by the use of more than one benzophenone [37], or combinations with other classes of stabiliser such as benzotriazoles or cinnamates [36], or in combination with antioxidants [41, 42]. 

Additive packages containing benzotriazoles along with other co-additives are also known. These include combinations with benzophenones and/or cinnamate-types [36] with antioxidants [41, 42] with fatty acid salts of manganese [55] combinations of polyoxyalkyene-based benzotriazoles and PEN used in PET [61] and benzotriazole plus poly(isobornyl acrylate) for the protection of polyalkylene naphthalates [62]. 

Of the various chemical classes of UV stabilizers that have been developed, the benzophenone and benzotriazole UV absorbers, the hindered amine light stabilizers (HALS), and their combinations continue to satisfy the UV stabilization requirements of most of the large-volume outdoor polymer applications. In addition, many new stabilizer chemistries, such as UV absorbers based on hydrox-yphenyl triazines, have been developed for more demanding applications or to satisfy specific market needs. Light stabilizers together with other additives (qv), such as antioxidants (qv), impact modifiers, colorants (qv), fillers, heat stabilizers (qv) and plasticizers (qv), have enhanced the properties and extended the service life of polymeric materials, resulting in the replacement of traditional materials in a multitude of outdoor weatherable applications. 

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