Polymerization with Redox Systems as Initiators

In a redox system consisting of a peroxo compound and an iron(II) salt, the initiating radicals are formed by electron transfer from Fe to the peroxo compound, causing the peroxy link to be cleaved, with simultaneous formation of a radical and an anion. In a second step, the oxidized metal reacts with another hydroperoxide to form a peroxy radical and a proton  

Hydrogen peroxide Peroxodisulfates Diacyl peroxides Hydroperoxides Peracid ester Ag+,Fe2+,Co +,Tp+ Hydrogen sulfites, sulfites, thiosulfates, mercaptans, sulfinic acids Amines (e.g. NdV-dimethylaniline), certain sugars Benzoin/Fe Hydrogen sulfite/Fe  

It must be emphasized that, in contrast to the initiation of polymerization with peroxo compounds or azo compounds, not every redox system is suitable for initiating polymerization of every unsaturated monomer. Before attempting to polymerize a new compound with a redox system it is, therefore, advisable first to test its radical polymerizability with dibenzoyl peroxide. 

Redox polymerizations are usually carried out in aqueous solution, suspension, or emulsion rarely in organic solvents. Their special importance lies in the fact that they proceed at relatively low temperatures with high rates and with the formation of high molecular weight polymers. Furthermore, transfer and branching reactions are relatively unimportant. The first large-scale commercial application of redox polymerization was the production of synthetic rubber from butadiene and styrene (SBR1500) at temperatures below 5 °C (see Example 3-44). 

Peroxodisulfates Hydrogen sulfites, sulfites, thiosulfates, mercaptans, sulfinic acids 

Diacyl peroxides Amines (e.g. iVdV-dimethylaniline), certain sugars 

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