Zinc complexes containing asymmetrical N,N,O-tridentate ligands and their application in lactide polymerization?

Dalton Transactions Pub Date: 2013-09-03 DOI: 10.1039/C3DT52016A

Abstract

A series of zinc complexes based on asymmetrical N,N,O-tridentate ligands were prepared via binaphthyl diamine derivatives. These complexes were characterized and employed as catalysts in lactide polymerization. The X-ray diffraction analyses revealed that molecular structures of 1b and 2b were mononuclear complexes with zinc atoms in distorted octahedral geometries. Upon co-catalysis with isopropanol, complex 2a showed the highest activity among these zinc complexes for the ring-opening polymerization of L-lactide, and complex 3a exhibited the highest stereoselectivity for the ring-opening polymerization of rac-lactide affording substantially isotactic polylactide (PLA) with a Pm of 0.62. The polymerization kinetics using 2a as a catalyst was studied in detail. The kinetics of the polymerization results revealed that the rates of polymerization were first-order both in the monomer and the catalyst, and there was a linear relationship between the L-LA conversion and the number-average molecular weight of PLA with a narrow molecular distribution (1.07–1.17). The activation energy (31.49 kJ mol?1) was deduced according to the Arrhenius equation.

Graphical abstract: Zinc complexes containing asymmetrical N,N,O-tridentate ligands and their application in lactide polymerization
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