Nickel Catalysts for Ethylene Homo- and Co-Polymerization

Summary

Nickel compounds based upon phosphorus-oxygen chelate ligands, Ph₂PCR=CRO⁻, are effective catalysts for the homopolymerization of ethylene to high molecular weight polyethylene. They will also copolymerize ethylene with alpha-olefins, and more importantly, with polar monomers and carbon monoxide.

When L is PPh₃ or other phosphine ligands, a cocatalyst is required to scavenge the phosphorus ligand. This cocatalyst can be Ni(COD)₂, Rh(acac) (C₂H₄)₂, or Me₃N=0. Alternatively, it is possible to prepare “lightly ligated” complexes with ligands like pyridine or “unligated” dimer complexes in which the oxygen atoms of the chelate ligands bridge two nickel centers. These species act as single component catalysts.

These catalysts, are resistant to a variety of polar molecules such as nitriles, alcohols, and even water. They will copolymerize ethylene with a variety of polar comonomers under mild conditions to yield functionalized linear low density polyethylene (FLLDPE). Introduction of carbon monoxide to an active ethylene polymerization yields a rigorously alternating, 1:1 copolymer of ethylene and CO. If the complexes are exposed to CO before the ethylene polymerization is initiated, CO inserts into the Ni-Ph bond giving the benzoyl complex. The reaction continues, giving Ni(0) carbonyl complexes and the benzoic ester of the vinyl chelate ligand, Ph₂PCH=C(Ph)OC(O)Ph.

To be submitted to the Proceedings of the International Symposium on Homogeneous Catalysis, Kobe, Japan, September 22, 1986, Journal of Molecular Catalysis