For the interpretation of the effect of such pi-donors as durene and tetraphenylethylene on the observed rate constant of the styrene anionic polymerization in cyclohexane, quantum-chemical DFT calculations of the structures and relative stabilities of the polymerization active sites, their dimeric associates and complexes with the pi-donors were performed. It was shown that pi-donors stabilize the propagating monomeric chain-ends, PStLi, facilitating the deaggregation of the (PStLi)(2) dimers. The calculations showed that the formation of the PStLi complexes with one and two durene molecules is possible. In agreement with the experimental kinetic data, it was shown that the higher is the number of durene molecules complexed to the active site, the lower are its ability to bind styrene and, thus, its propagating activity. Therefore, addition of pi-donors initially leads to an increase in the observed polymerization rate constant due to active chain-ends being deaggregated. However, after a maximum, further addition of pi-donors decreases the observed polymerization rate constant due to decreasing propagating ability of active sites complexed with pi-donors. (C) 2003 Published by Elsevier Ltd.