| Miniemulsion polymerization is differentiated from emulsion polymerization by the fact that the monomer droplets are smaller than found in emulsion and can compete effectively with micelles in the nucleation of polymer particles. To achieve the droplet sizes necessary, high shear is used with surfactants and cosurfactants. The term cosurfactant refers to organic additives which are not surface active but which enhance the stabilization properties of the surfactant. The mechanism of miniemulsion polymerization is different because of the role of the droplets as potential polymer particles. In this work, continuous polymerization in the emulsion and miniemulsion systems have been studied and compared both experimentally and through computer simulation.;Experimental polymerizations in a CSTR have shown that, at low residence times, the emulsions oscillate in conversion whereas the miniemulsions do not. The conversion oscillations in emulsion polymerization are due to the alternating presence and absence of micelles in the reaction mixture. In the miniemulsions, the lack of oscillations clearly points to the reduced role of micelles. Further, the miniemulsions achieved a polymerization rate twice that of the classic emulsions. The particle size and conversion data indicate that more particles are present in the miniemulsions. The molecular weight data indicate a significant degree of radical segregation in both systems.;Other experimental data show that the polymerization rate in the miniemulsion system is a function of the concentration of monomer droplets. In the emulsion system, the polymerization rate is a function of the concentration of micelles. The source of particle formation in the two systems is different. In the miniemulsion system, the monomer droplets are the primary source of polymer particles while micelles are the main source of polymer particles in the emulsion system.;Mathematical models have been developed which describe the emulsion and miniemulsion systems. While predictions of the dynamic behavior of the systems are beyond the scope of these models, good agreement between simulation and experimental results have been obtained at steady state reactor conditions. In addition, it is also shown that the models predict more polymer particles in the miniemulsion system than in the emulsion, as was observed in the experiments. |
