Miniemulsion Copolymerization in Batch and Continuous Reactors

Abstract

Conventional emulsion polymerization (also called macroemulsion polymerization) has been widely used in a variety of industries whereas nucleation and polymerization directly in submicron monomer droplets (i.e., miniemulsion polymerization) has been primarily an academic curiosity. However, much interest has recently been generated on the basis of the prospects of incorporating very hydrophobic ingredients into a water-based system via miniemulsion polymerization. In this work, a very hydrophobic acrylic monomer, 2-ethylhexyl acrylate, is copolymerized with methyl methacrylate using a miniemulsion recipe. The goal of this paper is to examine emulsion copolymerization kinetics for monomers of very different water solubilities. It is believed that the effects of water solubility differences between comonomers are minimized using a miniemulsion recipe. In this case, the copolymer composition is more uniform in batch miniemulsion copolymerization experiments, relative to batch macroemulsion copolymerizations. The same behavior is, however, not observed in a continuous-stirred tank reactor. At even moderate steady-state conversions, there is a substantial driving force for monomer transport that favors incorporation of the more water-soluble comonomer.