AbstractThe kinetics of the anionic ring‐opening polymerization of the DDNMe cyclodisilazane, initiated by benzyllithium, has been investigated in different experimental conditions. In non‐polar solvents, the active centers are aggregated ion pairs which are in equilibrium with a small amount of monomeric species. In the presence of additives such as THF, dioxane or tetramethyl‐ethylenediamine, there is only one type of active center. The aggregates are dissociated into light ion pairs externally solvated by the additive. The paper demonstrates also that the kinetics of the polymerization (i.e., rate constant of propagation kp) is a function of both the nature and the amount of additives.