Anionic polymerization of lactones initiated by alkali graphitides. V. Initiation mechanism and nature of the active centers

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Abstract
The initiation mechanism of the anionic polymerization of ϵ‐caprolactone (ϵ‐CL) under the action of the potassium graphitide KC24 was studied by 1H‐NMR spectroscopy of low molecular weight products of the polymerization. On the basis of the experimental results, the assumption was made that the initiation proceeds through a proton transfer from the monomer to the initiator. From the results of end group analysis it was assumed that the active centers of the growing polymer chain are of an alcoholate type. Comparative investigations were performed on the mechanism of ϵ‐CL polymerization under the action of anion‐radicals (potassium‐naphthylide) and alkali metals (K‐mirro). The results obtained showed that anion‐radicals initiate the polymerization predominantly via addition to the monomer and the pure alkali metals by proton transfer from the monomer to the initiator. The active centers of propagation in these systems were most probably of an alcoholate type in spite of the difficulties for direct proof of their nature.