A model based on independently validated stabilization and rate data is used to quantify the rate of formation of particles during the dynamic nucleation stage of a batch emulsion polymerization reaction. Population balance equations (PBEs) that combine kinetic data validated in the absence of coagulation and a DLVO stability model with parameters validated in the absence of reaction were used to account for both micellar and homogeneous nucleation, as well as particle stabilization and growth. The model was tested in different polymerization systems at different ionic strengths. It is shown that a large number of moderately short-lived particles are formed during the early stages of nucleation and that they contribute to an accelerated rate of polymerization for a short period of time before coagulating onto large structures in the reactor. (c) 2005 American Institute of Chemical Engineers.