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

Abstract

Aqueous free radical polymerization or methyl methacrylate monomer [M], initiated by manganese (III) pyro phosphate- potassium thiocyanate redox system, has been studied in the <i>p</i>H range 2-3 and in the temperature range 25- 40^o Cat 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 or the rate has been studied and the activation parameters computed using the Arrhenius plot. A polymerization mechanism, in volving chain initiation by radicals derived from decomposition or manganese (III)-thiocyanate complex formed <i>in situ </i>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]^1/2, [Mn(II)^-1/2, [P₂O₇^4-]^-1/2. The overall energy of activation in the range studied (25-40^oC) is round to be 32.2 kJ mol^-1.