The preparation of surface-functional monodisperse nanoparticles with surfactant-free emulsion polymerization using polymerizable functional surface-active monomers was investigated. Crosslinked styrene seed latex to be used in the second-stage polymerization of styrene with SPM or SPE was synthesized. The seed latex was characterized by particle size and size distribution. In the second stage of a starved-feed polymerization of styrene with SPM, a water-soluble azo initiator and an oil-soluble azo initiator were used separately, and the relevant mechanistic characteristics, mainly competitive growth, were compared with data obtained from Zetasizer and atomic force microscopy measurements. The mechanism of competitive growth was the same in both systems. The oil-soluble azo initiator also was used in the second-stage, starved-feed polymerization of styrene with SPE. Latices were cleaned by the serum replacement technique and ion exchange method. Particle size data clearly suggested a bimodal particle size distribution during the first 2 h of polymerization. The bimodality originated from the fractions of different-sized particles in the seed latex competing for the available monomer. The two particle size fractions in the early stages of polymerization tended to merge after 2 h, a situation that satisfied the conditions of a competitive growth mechanism. (c) 2006 Wiley Periodicals, Inc.