Group-transfer polymn. of Me methacrylate (I) in THF with (1-methoxy-2-methyl-1-propenyloxy)trimethylsilane (II) as initiator and Bu4NCN as catalyst was investigated. Beside a fast isomerization, only very slow dimerization reactions of the initiator in the presence of the catalyst were obsd. Therefore, the system behaved like a living one. Values of .hivin.Mw.hivin.Mn approached 1.3 at low catalyst concns. Tacticity measurements yielded about 60% syndiotactic, 36% heterotactic, and 3% isotactic triads. Induction periods in time-conversion curves obtained with II as initiator and intercepts in the plots of the no.-av. mol. wt. vs. monomer vanished, when the reaction was initiated with the first addn. product of II and I. This is assumed to be a strong indication, that in the investigated system a slow initiation step between II and the first I unit precedes the propagation reaction.