Monodispersed copolymer emulsions, each with a different polymer particle size, were used to investigate the effect of particle size on the electrical and thermomechanical properties of carbon black (CB)-filled segregated network composites. These emulsions were synthesized with equal moles of methyl methacrylate and butyl acrylate, with latex particle size ranging from 83 to 771 nm. The electrical percolation threshold was found to decrease from 2.7 to 1.1 vol % CB as the latex particle size was increased. Microstructural images reveal diminished latex coalescence, and improved CB segregation, with increasing latex particle size. In general, coalescence is shown to increase for all systems with increasing CB concentration. Furthermore, all systems exhibited a similar maximum electrical conductivity plateau of 0.7 S cm(-1), albeit at lower concentration for larger latex particle size. This ability to tailor percolation threshold with latex particle size provides an important tool for manipulating electrical and mechanical properties of polymer nanocomposites. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1547-1554, 2011