Effect of thiourea on the radical polymerization of vinyl monomers. Part I. Polymerization of acrylonitrile with the hydrogen peroxide–thiourea catalyst system

Abstract

Abstract The polymerization of acrylonitrile (AN) was studied in aqueous solution with hydrogen peroxide (H 2 O 2 ) as catalyst and thiourea (TU) as cocatalyst at 30°C. Since the polymerization was carried out at a relatively low temperature, AN was not polymerized by hydrogen peroxide alone. Upon addition of TU to the reaction system, polymerization occurred immediately, and the rate of polymerization increased with increasing TU concentration. In order to obtain the overall polymerization equation, the dependence of polymerization rate on H 2 O 2 and AN concentration was studied kinetically. It was found that the overall polymerization rate R p was represented by the equation: R p = K [TU] frac12; [H 2 O 2 ] frac12; [AN], where K is the rate constant. The acceleration in the presence of TU might be attributed to a redox reaction between H 2 O 2 and TU which would produce free radicals rapidly. The effect of substituents was investigated by use of various N ‐substituted derivatives of TU. The polymerization rate increased linearly with the σ * constants of the substituents as electron‐withdrawing substituents were added. The polymerization mechanism is discussed on the basis of the results.