Polymer-stabilized miniemulsion polymerization in a continuous stirred-tank reactor

Conventional emulsion polymerization (also called macroemulsion polymerization) has been widely used in a variety of industries whereas nucleation and polymerization directly in sub-micron monomer droplets (i.e. miniemulsion polymerization) has been primarily an academic curiosity. However, much interest has been generated recently based on the prospects of incorporating very hydrophobic ingredients into a water-based system via miniemulsion polymerization. Miniemulsions are produced by the combination of a high shear device to break up the emulsion into sub-micron monomer droplets and a water-insoluble, monomer-soluble component, referred to as a hydrophobe, to retard monomer diffusion from the sub-micron monomer droplets.; Polymeric hydrophobes have been shown to be sufficient to effect predominant droplet nucleation and to eliminate conversion oscillations often observed for macroemulsion polymerization in a CSTR. The latter result is attributed to the fact that miniemulsion polymerization kinetics are more similar in batch and continuous reactors than are macroernulsion polymerization kinetics. However, copolymer composition using a miniemulsion polymerization recipe is not necessarily the same in batch and continuous reactors. If one of the comonomers is extremely water-insoluble, than the polymer particles in a steady-state CSTR are richer in the more water-soluble monomer due to monomer transport from fresh monomer droplets entering the reactor in the feed stream. High intensity shear is typically provided by a sonicator, although continuous sonication may not be practical for large-scale production of commercial miniemulsion polymers. A rotor-stator type mechanical homogenizer has been used here to effect predominant droplet nucleation in a CSTR.; It has been shown in this work that continuous reactors are more effective than batch reactors for evaluating the preponderance of droplet nucleation for emulsion polymerization reactions. Predominant droplet nucleation has shown a significant dependence on the initial monomer droplet concentration, therefore factors affecting the concentration of monomer droplets, such as dispersed phase viscosity and emulsification intensity, are critical in continuous miniemulsion polymerization reactions. Monomer transport was found to have a slight effect on initial monomer droplet concentration but monomer transport is very important for miniemulsion copolymerization reactions in a CSTR.