Fast-Tracking the l -Lactide Polymerization Activity of Group 4 Metal Complexes of Amine Tris(phenolate) Ligands

Rami Hador, Michael Shuster, Sophia Lipstman, Moshe Kol

Research output: Contribution to journalArticlepeer-review

Abstract

Zirconium complexes of amine tris(phenolate) ligands wherein the substituents ortho to the phenolate oxygens are aryl groups are introduced, and their application in the catalysis of ring-opening polymerization of l-lactide at 180 °C is described. Spectroscopic and crystallographic characterization revealed that for ortho-phenyl substituents, bridging dinuclear complexes were obtained, whereas for ortho-mesityl-substituents, fluxional mononuclear complexes were obtained. Melt polymerizations employing catalyst ratios reaching as low as 5 ppm for unpurified l-lactide and 1 ppm for purified l-lactide revealed ultra-high activities for the zirconium complex featuring the mesityl-phenolate substituents, yielding high-molecular-weight stereoerror-free poly(l-lactic acid) that exhibited enhanced stability toward thermal degradation. Slightly lower activities were found for the corresponding hafnium complex and for the zirconium complex featuring the phenyl-phenolate substituents. These catalysts could thus serve as drop-in replacement for the industrially employed stannous octanoate.

Original languageEnglish
Pages (from-to)4872-4879
Number of pages8
JournalACS Catalysis
DOIs
StateAccepted/In press - 2022

Keywords

  • amine tris(phenolate)
  • hafnium
  • poly(lactic acid)
  • ring-opening polymerization
  • tripodal ligands
  • zirconium

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