Coordination insertion polymerization is an attractive method to synthesize polyolefins due to its ability to give precise control over the polymer microstructure. Pd complexes with phosphine-phosphine oxide ligands can copolymerize ethylene with a variety of polar olefins. However, these polar monomers decrease significantly the catalyst’s activity and the polymer molecular weights compared to polymerizations performed using non-polar monomers. It is believed that the formation of metal-monomer chelate complexes prevents efficient copolymerization. To avoid the generation of such intermediates, we designed cationic Pd complexes with polyethylene glycol (PEG) chains that can coordinate with alkali metal cations as secondary metal binding sites. 1H NMR Job plot studies showed that a 1:1 binding stoichiometry between Pd and alkali ion can be achieved and the tetraethylene glycol group has preference for the coordination of Na+ over Li+ and K+. The structure of the heterobimetallic palladium-sodium species was confirmed by X-ray crystallography. Our ethylene polymerization studies indicated that the addition of alkali ions to these complexes could enhance their ethylene polymerization activity. The heterobimetallic complexes also exhibit higher copolymerization activity and different polymer morphologies compared to their parent mononuclear complexes.

Copolymerization of ethylene and polar olefins by heterobimetallic catalysts with phosphine-phosphonate ligands

255th National Meeting (2018)

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