Nonconventional emulsion polymerization of methyl methacrylate. Effect of Cu(II)/histidine complex catalyst and different peroxo-salts

The characteristics of nonconventional (soap-free) aqueous emulsion polymerization reactions of methyl methacrylate were evaluated by the catalytic effect of in situ developed different transition metal (11) chelate complex with amino acids initiated by different peroxo salts like potassium monopersulfate (KMPS, KHSO5), potassium persulfate (KPS, K2S2O8), ammonium persulfate (APS, (NH4)(2)S2O8). From the comparative data, the CuSO4/histidine chelate complex was selected as a novel catalyst for a detailed kinetic and spectrometric study of polymerization. Both kinetic and thermodynamic aspects of the polymerization dictate which initiator and particle morphology are obtained. The complex catalyzed polymerization proceeded smoothly until high conversion and yielded stable emulsions. The apparent activation energies (E.) for the complex catalyzed emulsion polymerization were computed for different initiators to be 34, 38, and 46 kJ mol(-1), each a very low value. Use of these values and activation energies of propagation and termination for MMA gave an unexpectedly low activation energies (E-d, 26, 34, and 51 kJ mol(-1) for KMPS, KPS, and APS respectively) to the decomposition of different persulfate initiators in the complex catalyzed system. The emulsion polymer latex was characterized through the determination of average molecular weights of the purified polymers by gel permeation chromtography (GPC) and viscosity methods and the morphology by scanning electron microscopy (SEM). The coordination complex catalytic system shows excellent industrial performance characteristics in preparing micro- to nano-scale latex particles.