Aqueous polymerization of methyl methacrylate initiated by manganese (III)pyrophosphate - potassium thiocyanate redox system: A kinetic study

Aqueous free radical polymerization of methyl methacrylate monomer [M], ini tiated by manganese (III) pyrophosphate - potassium thiocyanate redox syste m, has been studied in the pH range 2-3 and in the temperature range 25-40 degrees C at constant ionic strength. The rates of polymerization (R-p) and manganese (III) disappearance have been measured. The effects of certain s alts, water miscible organic solvents, and surfactants on the rate of polym erization have been investigated, The temperature dependence of the rate ha s been studied and the activation parameters computed using the Arrhenius p lot. A polymerization mechanism, involving chain initiation by radicals der ived from decomposition of manganese (III)-thiocyanate complex formed irt s itu and bimolecular chain termination, is suggested. The rate of polymeriza tion is found to be proportional to [M](1,2), [Mn(III)](1/2), [H+](1/2), [N CS-] , [Mn(II)](-1/2), [P2O74-](-1/2). The overall energy of activation in the range studied (25-40 degreesC) is found to be 32.2 kJ mol(-1).