Polymer-bound antioxidants approaches

The reasons for the present interest in polymer-bound antioxidants is discussed, and some of the more important approaches to the chemical attachment of antioxidants and stabilizers to polymer molecules are briefly reviewed. 

Approaches to Polymer-Bound Antioxidants. Three basic methods of... 

A logical approach to persistent antioxidants is to attach the antioxidant to the polymer chain. Polymer-bound antioxidants are effective and a number of methods have been employed to attach them to the polymer. Copolymerization is not often used, since it requires the production of special batches of polymer for each particular application. A favored method is to develop additives that can be coupled to the polymer during processing (Scott, 1987 Munteanu, 1987). Polymer-bound antioxidants are... 

Another approach was developed by Scott in the 1970 s (7.8) which utilises the same mechanochemistry used previously by Watson to initiate the Kharacsh-type addition of substituted alkyl mercaptans and disulphides to olefinic double bonds in unsaturated polymers. More recently, this approach was used to react a variety of additives (both antioxidants and modifiers) other than sulphur-containing compounds with saturated hydrocarbon polymers in the melt. In this method, mechanochemically formed alkyl radicals during the processing operation are utilised to produce polymer-bound functions which can either improve the additive performance and/or modify polymer properties (Al-Malaika, S., Quinn, N., and Scott, 6 Al-Malaika, S., Ibrahim, A., and Scott, 6., Aston University, Birmingham, unpublished work). This has provided a potential solution to the problem of loss of antioxidants by volatilisation or extraction since such antioxidants can only be removed by breaking chemical bonds. It can also provide substantial improvement to polymer properties, for example, in composites, under aggresive environments. 

The above approach of mechanochemically initiated addition of reactive antioxidants on different polymers, such as rubbers and unsaturated thermoplastics such as ABS is illustrated here for thiol-containing antioxidants. For example, using thiol compounds (37) and (38) as the reactive antioxidants, Kharasch-type addition of the thiol function to the polymer double bond takes place during melt processing to give bound antioxidant adduct (see reaction 7) the polymer becomes much more substantive under aggressive environments. 

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