The influence of 1-pentanol (C5OH) on the ST emulsion polymerization mechanisms and kinetics is investigated. The CMC of the ST emulsions first decreases rapidly and then levels off when the C5OH concentration ([C5OH]) increases from 0 to 72 mM. The effect of C5OH increases to a maximum and then decreases when the SDS concentration ([SDS]) increases from 2 to 18 mM. At [SDS] = 2 mM, homogeneous nucleation controls the polymerization kinetics regardless of [C5OH]. At [SDS] = 4 mM, the effect Of [C5OH] appears due to the transition from homogeneous nucleation to a mixed mode of particle nucleation (homogeneous nucleation and micellar nucleation) occurs when [C5OH] increases from 0 to 72 mM. The effect Of [C5OH] is the strongest at [SDS] = 6 mM since the particle nucleation mechanisms span homogeneous nucleation (low [C5OH]), a mixed mode of particle nucleation (homogeneous nucleation and micellar nucleation) (medium [C5OH]) and micellar nucleation (high [C5OH]). At [SDS] > 6 mM, in which micellar nucleation controls the polymerization kinetics, the effect Of [C5OH] decreases rapidly with increasing [SDS]. (C) 2004 Elsevier Ltd. All rights reserved.