Modeling and simulations of nitroxide-mediated radical polymerization (NMP) in dispersed systems have been performed to elucidate what factors dictate the magnitude of the segregation effect on bimolecular termination between propagating radicals generated from alkoxyamine activation. The reduction in termination rate due to segregation cannot be predicted merely based on the average number of propagating radicals per particle ((n) over bar (p)). This is because the magnitude of the segregation effect is also governed by the distribution of propagating radicals between particles, which is influenced by both the termination (k(t)) and the deactivation (k(deact)) rate coefficients. The results have implications with regards to improvement of livingness (end-functionality) in NMP by exploitation of particle size, and are expected to apply (qualitatively) to other controlled/living systems based on the persistent radical effect (e.g. atom transfer radical polymerization). (C) 2010 Elsevier Ltd. All rights reserved.