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Purealuminum isopropoxide was shown to be a highly active catalyst for the polymcrization of c-caprolactone: the overall kinetics of this polymerization follow a first current order in monomer and a first order in catalyst.Mechanistical studies indicate also that this system operates through a selective acyloxygen cleavage of the lactonc ring, with insertion in the aluminum-oxygen bond.Morcovcr, the polymcrization proceeds by a perfectly "living" process on catalytic coordination aggregates. ZlJSA M M EN FASSU NG :Es wird gezeigt, dab sich reines Aluminiumisopropoxid als cin hochaktiver Katalysator bei der Polymerisation von c-Caprolacton bewahrt : die Gesamtkinetik dieser Polymerisation 1st crstcr Ordnung fur das Monomer und erster Ordnung fur dcn Katalysator.Eine mcchanistische Untersuchung zeigt auch, daR dieses System eine selektive AcylSauerstoff-Spaltung des Lactonringes bewirkt, und m a r durch Einschiebung in die Aluminium-Sauerstoff-Bindung.AuRerdem lauft die Polymerisation an katalytischcn Koordinationsaggregaten. nach dem Prinzip ,,lcbender" Systcmc ab.

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The ring‐opening polymerization of unsubstituted lactones by Al2Zn and Al2Co(II) μ‐oxoalkoxides in homogeneous organic phase is described. Under these conditions, the chain propagation is very fast and proceeds without transfer or termination reactions. The composition and structure of the main products resulting from the first polymerization steps have been determined, and fit with a monomer insertion mechanism into the aluminum‐alkoxide bonds of the catalyst.

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