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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.

SynopsisThe fast and living ring-opening polymerization of lactones by bimetallic p-oxoalkoxides in homogeneous organic phase has led to successful block copolymerization. The catalyst is coordinatively associated in organic media; however, interaction with lactones can induce, following their nature, different rearrangements of the catalytic aggregates, depending on the nature of these lactones. Consequently, c-caprolactone and 0-propiolactone block copolymers are quantitatively obtained only in the presence of a completely dissociated catalyst.

Communications to the Editor 651 Table III Specific Retention Volumes for Poly(dimethylsiloxane)-Hydrocarbon Systems at 40°V g°(cm3/mole) Column 1 2 3 4 5

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