In this study, we examined two types of oil water, two-phase system polymerization by designing droplets of reaction space aiming precise control of polymer particle properties: (i) suspension polymerization using emulsion droplets, and (ii) slug polymerization using slugs of the segmented flow. For suspension polymerization, the particle size can be controlled up to a limited extend by varying the droplet size. And slug polymerization, which we proposed as a new polymerization method, enables continuous production of particles and independent control of polymer properties by separating the molecular control and precipitation processes. Our proposed method can be expected to contribute to precise control of polymerization reactions. (C) 2009 Elsevier Ltd. All rights reserved.