Aluminum amine-(bis)phenolate complexes for ring-opening polymerization of rac-lactide and ε-caprolactone

Abstract

Five aluminum-based amine-bis(phenolate) complexes, three of them novel, with variation of the pendant donor arm were synthesized in excellent yields, and characterized by NMR spectroscopy and X-ray crystallogra-phy. The quantitative conversion of the aluminum alkyl species to the corresponding benzyl alkoxide was achieved by the addition of 1 mol eq. of benzyl alcohol, and was confirmed by 1H NMR spectroscopy. The aluminum alkox-ides were excellent mediators for the ring-opening polymerization (ROP) of rac-lactide, yielding atactic poly(lactic acid), having excellent correlation between theoretical and calculated molecular weights accompanied by narrow molecular weight distributions. ROP of ε-caprolactone by the aluminum alkoxides showed modest con-trol at 50°C in toluene, but much greater control was achieved when polymerizations were conducted at 25°C, with nar-rower molecular weight distributions observed in some cases. A relationship between the complex pendant donor arm and the resulting activity in the ROP of both rac-lactide and ε-caprolactone is discussed. Supplementary information is available at https://www.icevirtuallibrary.com/doi/suppl/10.1680/gmat.12.00006