The propagation reaction in the anionic polymerization of styrene with lithium as counter ion in cyclohexane has been investigated for six different concentrations of 1,2,4,5-tetrametbylbenzene (durene) in the range of living ends concentration between 10(-5) and 10(-3) M at 20 degreesC. The values of the apparent dissociation constant of PStLi dimer and the weighted rate constants of all unassociated species were obtained for all six investigated concentrations of durene. The apparent dissociation constant increases several orders and the weighted rate constants of all unassociated species decreases one or two orders depending on the concentration of durene. A new mechanism was proposed and the values of the relevant absolute propagation rate constants of the three reactive monomeric species have been for the first time derived from the kinetic results. The absolute propagation rate constants of PStLi.D and PStLi.2D are comparable but much lower than that of PStLi. The complexation constant of PStLi with one molecule of durene is much larger than that of PStLi with a second molecule of durene. (C) 2003 Elsevier Ltd. All rights reserved.