AbstractThe kinetics of initiation of the polymerization of 2,2,5,5‐tetramethyl‐1‐oxa‐2,5‐disilacyclopentane (2) with sodium phenyldimethylsilanolate1aand two of its phenyl substituted derivatives was investigated as model reaction for studying the initiation and crosspropagation steps in anionic polymerization of cyclic siloxanes in non‐polar media.A redistribution of siloxane units between living ends of the polymer and also between living end and initiator was demonstrated to occur commonly in the siloxane anionic polymerization system affecting the initiation and crosspropagation.However, the living silethylenesiloxane polymer system3showed no redistribution and the initiation, followed by the dissapearance of phenyldimethylsilanolate, showed a first internal order and a fractional external order with respect to the initiator. The same fractional order was found in the propagation step with respect to the living ends. The results can be rationalized on the basis of a mechanism in which silanolate groups aggregation (cyclic or cage structures) convert active species into dormant centres. The analysis of the kinetic scheme including the formation of simple and mixed aggregate series of optional multiplicity leads to the conclusion that the scheme under some assumptions suits the kinetics observed. Solvation processes as well as the increase of the negative charge density on the silanolate oxygen by electron releasing substituents increase the reactivity of the