Poly(methyl methacrylate) nanoparticles are synthesized via differential microemulsion polymerization, where the monomers in the reaction system are kept at very low concentrations by continuous differential addition. The effects of various reaction conditions, such as initiator, surfactants, reaction temperature and monomer loadings, on the particle size and molecular weight have been investigated. The effects of initiator and reaction temperature on latex particle numbers and polymer chain numbers within the particles were also investigated. It was observed that the dependence of particle size on reaction temperature and initiator concentration was non-monotonic. The optimized conditions were screened to prepare nanoparticles with the smallest size. (C) 2012 Elsevier Ltd. All rights reserved.