Uniformly sized porous polymer particles with different polarity namely poly(divinylbenzene), poly(vinyl acetate-co- divinylbenzene), poly(ethylene dimethacrylate), and poly (glycidyl methacrylate-co-ethylene dimethacrylate) were prepared in the micron-size range by a seeded polymerization method. Parameters affecting the particle morphologies including monomer mixture content, porogen content, and polystyrene (PS) seed latexes were varied, and the morphologies of the resulting particles were investigated by scanning electron and confocal microscopy. The results obtained indicated that the particle shape depended dominantly on the molecular weight of the PS seed template. Deformed particles, including collapsed spheres and spheres with holes were obtained when high molecular weight PS seeds were used, whereas well-defined polymer particles were produced easily by using low molecular weight seeds. The use of 1,1-diphenylethylene as a chain terminator during seed polymerization is proposed in this work as an efficient method to lower molecular weight of PS in seed particles while keeping seed size small. This low molecular weight seed template retained its spherical geometry after swelling and polymerization with different second stage monomers. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2070-2080, 2011