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Aluminum alkoxide catalysts with bulky adamantyl groups accelerate the polymerization of ε-caprolactone. Steric bulk on the catalyst ligands favorably alters geometry, reducing energy barriers for faster polymer production.

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Area of Science:

  • Organometallic Chemistry
  • Polymer Science

Background:

  • Salen ligands are versatile scaffolds for metal complexes.
  • Aluminum alkoxides are active catalysts for ring-opening polymerization.

Purpose of the Study:

  • To synthesize and evaluate aluminum alkoxide-salen complexes for ε-caprolactone polymerization.
  • To investigate the influence of ligand structure, specifically ortho-adamantyl substituents, on catalytic activity.

Main Methods:

  • Synthesis of aluminum alkoxide complexes with tailored salen ligands.
  • Kinetic studies of ε-caprolactone polymerization.
  • Density Functional Theory (DFT) modeling of reaction mechanisms.

Main Results:

  • Catalysts exhibited coordination geometries intermediate between square-pyramidal and trigonal-bipyramidal.
  • Ortho-adamantyl substituents significantly enhanced catalyst reactivity.
  • Kinetic and DFT studies revealed that bulky substituents lower the activation energy for the rate-limiting step.

Conclusions:

  • Ligand design, particularly the steric bulk of ortho-substituents, is crucial for tuning the performance of aluminum alkoxide catalysts.
  • Favorable distortion of precatalyst geometry by bulky groups accelerates ε-caprolactone polymerization.