Copolymerizing antioxidant functions

Features of the free-radical initiation processes are similar for both the homopolymerization of functionalized monomers and copolymerization of the latter with conventional monomers. Common chemical initiators were applied. Azo-bis(isobutyro nitrile) was mostly used in bulk polymerization. No interference with phenolic hydroxy groups was observed in polymerization of 2-hydroxybenzo-phenoiKs, acetophenones, salicylates and of their derivatives [47]. The most rigorous eliinination of oxygen from the reaction mixture was necessary to achieve polymerization of monomeric hindered phenolic antioxidants or derivatives of 2-(2-hydroxyphenyl)benzotriazole [48]. An oxygen-free atmosphere is also an advantage for aromatic amines. A higher initiator level and/or increased temperature appear to be necessary to achieve normal polymerization rates with (D-functionalized monomers [46]. 

In the case of synthetic elastomers formed by free radical emulsion techniques, monomers that contain both an antioxidant moiety and a polymerizable function can be copolymerized (6). A series of esters and amides containing the 4-anilinophenyl group or the 3,5-di- er -butyl-4-hydroxyphenol group and a polymerizable a, /3-unsaturated acyl group such as acryloyl or methacryloyl were incorporated into the polymer. 

Copolymerization during Polymer Manufacture. Extensive work has been documented on the synthesis and successful copolymerization of a large number of polymerizable UVA containing one or two UVA functions (see Scheme 24 for selected examples) (163,164). However, the use of such antioxidants has been beset by high ssmthetic costs. 

For very aggressive conditions, e.g. for the stabilization of plastics for use in the automotive industry, or for materials in contact with hot extracting media, oUgomeric or polymeric stabilizers are an option [5]. These systems have to be tailor-made for a particular host pol5nner, because of potential problems with reduced compatibility. Two examples are the oligomeric phenol XX, and the antioxidant XXI prepared by free-radical copolymerization or antioxidant XXII obtained by functionalization of a conventional pol)oner. In these persistent phenolics, the strict structural requirements assuring high chemical efficiency are fulfilled as well. 

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