Results of recent studies on anionic polymerization of p-lactones initiated by potassium methoxide/- or tert-butoxide/- 18-crown-6 complexes revealed that, independent of the alkoxide used, corresponding unsaturated esters (unreactive in further polymerization) and potassium hydroxide with complexed counterion of metal are the initial products of the first step of polymerization. The latter constitutes the real initiator in this system. It has been fund that potassium naphthalenide complex with 18-crown-6 or cryptand  constitutes a new useful initiator in the anionic polymerization of β-lactoncs. Potassium salts of respective α, β-unsaturated carboxylic acids initially formed due to the a-deprotonation of β-lactone molecule are able to propagate the polimer chain growth. Novel initiator - solutions of supramolecular alkali metal complexes in THF, e.g. K-, K+(18-crown-6) complex - was found to induce an unusual scission of the C(3)-C(4) bond of the β-lactone ring in the initiation step of polymerization and in the formation of corresponding cnolate carbanion responsible for further polymerization. „Living polymers" and block copolymers were obtained in this way. Irrespective of various mechanisms of the initiation step, induced by different anionic initiators, the polymer chain growth takes place on carboxylate active centres, due to the alkyl-oxygen bond cleavage in monomer molecule.
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