An unconventional amphiphile (1-[w-(4'-methoxy-4-biphenylyloxy)octyl]pyridinium bromide, PC8) was used as surfactant in the emulsion polymerization of styrene. At low surfactant concentration (6, 12 or 36 mmol l(-1)), curves of polymerization rate versus conversion obeyed the typical behavior characterized by intervals I,II and III. However, at high concentration (48 or 72 mmol l(-1)) the interval II was not observed. The particle size distribution curves showed two families of polymer particles, indicating the participation of at least two mechanisms of particle formation, one being the simple micellar nucleation and the other probably the coagulative nucleation of precursor particles. The latter was considered to occur during the nucleation interval. (C) 2003 Elsevier Ltd. All rights reserved.