Benzotriazole-antioxidant combination

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. 

Further examples reported in Table 40 arc given by the alkyl ketone moieties deriving from oxidation of polyenes, which arc subjected to Mannich aminomethylation in order to produce compounds 559 having dispersant properties for lubricating oils, by benzotriazoles 557, capable of forming, due to physical adsorption, thin layers over the surfaces subjected to friction, and by S-Mannich bases 558, combining antifriction and antioxidant properties. 

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. 

Highly effective UV stabilizing systems can also be achieved by using synergistic mixtures of photoantioxidants/stabilizers with complementary antioxidant mechanisms, e.g. the use of combinations of nickel complexes of dithioic acids, NiDRC, NiDRP, with UV absorbers such as UV531, or hindered piperidine light stabilizers with UV absorbers, e.g. the benzotriazoles. 

Yellowing in thermoplastic polyurethanes can be retarded by adding UV-stabilizers, antioxidants and/or reduction agents. Proven stabilizers are the combinations of a phenolic antioxidant with an absorber of the hydroxybenzophenone or the hydroxy-benzotriazole type, and the three-fold combination phenolic antioxidanf/UV absorber/sterically hindered amine. This has allowed significant improvements in the light resistance of thin cast films made from aromatic polyester urethane [86]. 

The hindered piperidines exhibit a complex behaviour when present in combination with other antioxidants and stabilizers. As discussed earlier (see Section 19.4.2.1), these have to be oxidized first to the corresponding nitroxyl radicals before becoming effective. Consequently, both CB-D and PD-C antioxidants which remove alkylperoxyl radicals and hydroperoxides respectively, antagonize the UV stabilizing action of this class of compounds. However, since the hindered piperidines themselves are neither melt nor heat stabilizers for polymers, they have to be used with conventional antioxidants and stabilizers. By contrast, the derived nitroxyl radicals are much more effective broad spectrum stabilizers, since not only are they more effective UV stabilizers but they are also highly efficient melt stabilizers and have some thermal antioxidant activity. Hindered piperidines have been reported to synergize with UV absorbers, e.g. the benzotriazole UV stabilizers, in different polymers such as polypropylene, polystyrene and ABS. ... 

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