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Monofunctional hyperbranched ethylene oligomers.

Thomas Wiedemann1, Gregor Voit, Alexandra Tchernook

  • 1Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz , 78464 Konstanz, Germany.

Journal of the American Chemical Society
|January 24, 2014
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Summary
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Nickel catalysts convert ethylene into hyperbranched oligomers. Catalyst substituents control branching and molecular weight, with one catalyst showing broad applicability. Functionalization with esters, alcohols, or epoxides is efficient and scalable.

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Area of Science:

  • Organometallic Chemistry
  • Polymer Chemistry
  • Catalysis

Background:

  • Developing efficient catalysts for ethylene oligomerization is crucial for producing value-added materials.
  • Hyperbranched polymers offer unique properties due to their globular structure and high functional group density.
  • Controlling polymer architecture and enabling selective functionalization are key challenges in polymer synthesis.

Purpose of the Study:

  • To synthesize and evaluate neutral κ(2)N,O-salicylaldiminato Ni(II) complexes as catalysts for ethylene oligomerization.
  • To investigate the influence of catalyst structure on hyperbranched oligomer properties, including branching density and molecular weight.
  • To develop scalable methods for selective monofunctionalization of the resulting hyperbranched oligomers.

Main Methods:

  • Synthesis of nickel(II) salicylaldiminato complexes with varying remote substituents (R = Me, Et, iPr).
  • Ethylene oligomerization reactions under varying pressures and temperatures using the synthesized catalysts.
  • In situ catalyst system preparation and evaluation.
  • Post-oligomerization functionalization via ethoxycarbonylation, cross-metathesis with ethyl acrylate followed by hydrogenation, and epoxidation.

Main Results:

  • All catalysts produced hyperbranched low-molecular-weight oligoethylenes (Mn ≈ 1000 g mol⁻¹) with high productivity.
  • Branching density decreased and molecular weight increased with bulkier substituents (Me > Et > iPr).
  • Catalyst 1a-pyr (R=Me) demonstrated robust performance across a wide range of reaction conditions.
  • An in situ system matched the activity and microstructure of pre-formed catalysts.
  • Selective introduction of ester, alcohol, and epoxide functional groups was achieved efficiently and scalably.

Conclusions:

  • Neutral salicylaldiminato Ni(II) complexes are effective catalysts for producing hyperbranched oligoethylenes.
  • Catalyst design allows tuning of polymer architecture and properties.
  • Scalable and efficient methods for monofunctionalization open avenues for creating novel functional materials.