Changes in the rate of anionic polymerization of octamethylcyclotetrasiloxane caused by the formation of complexes on silanolate active centers

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Abstract
The effect of bases on the anionic polymerization of octamethylcyclotetrasiloxane (tetramer) initiated by ∼Si—OK groups has been studied. In the presence of hydroxides of alkali metals or of other Lewis bases, in particular of anisole, complexes are formed on active centers which alter the reactivity of the centers. The effects of the presence of NaOH, LiOH, anisole, and excess KOH on the polymerization of tetramer initiated by ∼Si—OK groups have been determined at various temperatures. An explanation is proposed for the retardation effect of LiOH and NaOH on the polymerization of tetramer; the effects of anisole and excess KOH has been discussed. Also the molecular weight of polydimethylsiloxane is affected by the presence of bases. A hypothesis of the formation and decomposition of complexes on active centers has been formulated which can explain the observed changes in the molecular weight of the polymer. The overall energies of activation of tetramer polymerization initiated by KOH in the presence of LiOH, NaOH, excess KOH, and anisole have been measured. Also measured were values of equilibrium constants of reactions of formation and decomposition of complexes of ∼Si—OK groups with LiOH, NaOH, and KO∼Si— and the corresponding heats of reactions.