Nonconventional Emulsion Polymerization of Methyl Methacrylate. Effect of Cu(II)/Histidine Complex Catalyst and Different Peroxo-Salts

Abstract

ABSTRACT: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 (II) chelate complex with amino acids initiated by different peroxo salts like potassium monopersulfate (KMPS, KHSO 5 ), potassium persulfate (KPS, K 2 S 2 O 8 ), ammonium persulfate (APS, (NH 4 ) 2 S 2 O 8 ). From the comparative data, the CuSO 4 /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 a ) 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. KEY WORDS Complex Catalysis / Soap-Free Emulsion / Kinetics / Micro-Particles / Scanning Electron Microscopy (SEM) /In recent years number of papers have been published on emulsion polymerization of vinyl monomers using persulfates as initiators. 1-5 Also several studies were done in the emulsion polymerization of vinyl monomers using different redox pair initiation systems. [6][7][8][9][10][11][12][13] However the use of these initiation systems were not straight forward and often leads to low conversion of monomers to polymer in oxygen-free (inert) atmosphere. Again most of these processes were carried out at high temperatures, but none of these functioned suitably for commercial purpose.In our different publications we have reported the emulsifier-free emulsion polymerization of acrylonitrile initiated by potassium monopersulfate together with in situ developed complex initiating systems, such as Cu(II)/Glycine 14 and Cu(II)/H 2 Salen 15 with comparison of results of N 2 atmosphere with that of the O 2 atmosphere in order to design a simple low-cost polymerization technique.The present work attempts the study on the soapfree emulsion polymerization of MMA with novel catalytic action of in situ developed complex of Cu(II) salts with a series of water soluble amino acids initiated by three peroxo salts and describes the kinetic results and the morphology of particles...

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