Studies in polymerization XI. Reactions between polymer radicals and ferric chloride in non-aqueous media

Abstract

The polymerizations of acrylonitrile, methacrylonitrile and styrene have been studied in NN -dimethylformamide solution at 60°C in the presence of ferric chloride. In each case the participating radicals enter into a termination reaction with the salt, with reduction of the latter to ferrous chloride. The rate constants of these reactions have been evaluated from kinetic observations; styryl radicals are much more reactive towards ferric chloride than either acrylonitrile or methacrylonitrile radicals. This is the expected order if the reactions are of the electron-transfer type. It is shown that estimation of the ferrous salt produced provides a useful practical method for determining the rate of chain starting. In the case of styrene, the reactivity of the radicals is so great that induction periods are observed, from which the rates of chain starting may also be deduced. A general treatment of retarded reactions under certain simple conditions is given and applied to the styrene polymerization.