Yttrium alkoxides bimetallic

Aluminium alkoxides (especially aluminium isopropoxide), dialkylalumi-nium alkoxides, yttrium alkoxides, zinc alkoxides, aluminoxanes, zincoxanes, bimetallic -oxoalkoxides, aluminium porphyrins and aluminium Schiff s base complexes are the most representative coordination catalysts, containing multi-nuclear or mononuclear species, for lactone polymerisations (Table 9.5). 

Among the multinuclear and mononuclear active species evaluated for lactone polymerization, those effective for the polymerization of P-lactones implying an O-acyl scission (Scheme 9.16a) are aluminum and dialkylaluminum alkoxides, yttrium alkoxides, zinc alkoxides, aluminoxanes, zincoxanes, bimetallic g-oxoalkoxides and aluminum porphyrins of the (TPP)AIOR type [50]. However, aluminum porphyrins such as (TPP)AICI or (TPP)A10C(0)R and aluminum SchifFs base complexes such as (Sal)AlCl (where Sal = salcenato group) are able to promote lactone polymerization by O-alkyl scission (Scheme 9.16b) [50]. 

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