Microemulsion and emulsion polymerization can have some similarities in starting conditions and polymerization mechanisms, but the resulting latices are unalike in particle size and molecular weight. Here we show that polymerizations can be formulated that display the characteristics often separately associated with microemulsion or emulsion polymerization. Kinetic modeling and particle size measurements show that emulsion polymerizations with initial concentrations close to the microemulsion-emulsion phase boundary demonstrate relatively fast consumption of monomer droplets and produce smaller particles. Because of their high surfactant concentrations, none of the emulsion polymerizations examined demonstrate the classical Smith-Ewart kinetics usually associated with emulsion polymerization. Instead these emulsion polymerizations have a long period of particle nucleation that subsides only after the disappearance of monomer droplets. (C) 2004 Wiley Periodicals, Inc.