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], initiated by manganese (III) pyrophosphate - potassium thiocyanate redox system, 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 salts, water miscible organic solvents, and surfactants on the rate of polymerization have been investigated, The temperature dependence of the rate has been studied and the activation parameters computed using the Arrhenius plot. A polymerization mechanism, involving chain initiation by radicals derived from decomposition of manganese (III)-thiocyanate complex formed irt situ and bimolecular chain termination, is suggested. The rate of polymerization is found to be proportional to [M](1,2), [Mn(III)](1/2), [H+](1/2), [NCS-] , [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).