Changes in potential during polymerization in redox systems

Abstract

Extensive investigations carried out by Kern, Baxendale, Bacon, 1-3 and others of the use of redox systems as polymerization initiators have revealed that the initiation in redox system is based on the fact that the radicals forming (as intermediate productsj during the redox reaction form active complexes with monomer molecules. This effect has been studied in detail by Baxendale and colleagues2 in the hydrogen peroxide-ferrous salt system. Nascent hydroxyl radicals HOwere found to react with monomer molecules, thus creating reactive complexes.Kolthoff and colleagues4 explain similarly the mechanism of polymerization initiated by a system consisting of benzoyl peroxide and a salt of bivalent iron.The effect of other systems, e.g., those containing persulfates, has also been studied by some authors. l v 5These studies have established, by the way, that certain redox systems may have a different polymerization effect for different monomers and under different conditions. Since the investigations discussed above did not concern themselves with phenomena accompanying the reaction in each redox system (namely, the time-potential changes) we have undertaken to investigate potential changes in certain select systems, and to determine the relation to polymerization.For this we have chosen two different model systems: (1) methyl methacrylate polymerization in water emulsion, ( 2 ) acrylonitrile polymerization in aqueous solution. In the first case the oxidizer (benzoyl peroxide) was dissolved in a monomer phase, while the reducing agent (a salt of bivalent iron) was dissolved in the aqueous phase. In the case of acrylonitrile polymerization, both components of the redox system (the persulfate and the Fe+-+ salt) were dissolved in water.