Soap-free emulsion copolymerisations of styrene with (2-(methacryloyloxy) ethyl) trimethyl ammonium chloride (MATMAC) were performed both in aqueous medium and in the mixture of water and ethanol. On increasing the molar ratio of MATMAC/St from 0/90 to 5/90, the particle size decreased first and then increased in the absence of ethanol, whereas particle size progressively decreased in the presence of ethanol. The addition of ethanol in the polymerisation also influenced the polymerisation kinetics, the charge density of polymer latex particles, agglomeration of primary particles and polymer latex evolution mode. Effects of ethanol on the latex characteristics have been discussed in terms of particle formation mechanism. (C) 2000 Elsevier Science Ltd. All rights reserved.