Applications Of Redox, Lewis Acid And Ligand Control In Olefin Polymerization And Copolymerization

Since the discovery of Drent catalyst, neutral phosphine-sulfonate Pd （II） and Ni（II） catalysts, especially for palladium catalysts, have been widely studied for the homopolymerization of ethylene and copolymerization of ethylene with a variety of polar vinyl monomers. However, the complexity and cost of chemical synthesis increase exponentially for the generation of new phosphine-sulfonate catalysts and correspondingly new polymers. Therefore, the idea of temporally switchable polymerization is highly attractive. So we introduced the idea of redox control and lewis coordination control in order to adjust the whole process of polymerization. The earth abundant and low cost nickel catalysts generally suffer from drawbacks of low thermal stability and low polymer molecular weight, which are exponentially amplified in the presence of polar monomers. Also, we focus on the issues presented above.1. First, we demonstrated the neutral and oxidized palladium complexes containing ferrocene bridged phosphine-sulfonate ligands. The interconversion between the neutral and oxidized palladium complexes was facile and reversible. The activity of these palladium complexes could be controlled using redox reagents during ethylene homopolymerization, ethylene/methyl acrylate copolymerization, norbornene homopolymerization. Specifically in norbornene homopolymerization, the neutral complexes were not active at all while the oxidized counterparts showed appreciable activity. In-situ switching between the neutral and oxidized forms resulted in an interesting "off’and "on" behavior in norbornene homopolymerization. This is the first effective example of redox controlled olefin polymerization mediated by metal catalysts.2. Then, a series of phosphine-sulfonate nickel and palladium complexes [（o-R₂-PC₆H₄SO₃）M（allyl）] （M= Ni, Pd） were synthesized and characterized. The reaction of lewis acid B（C₆Fs）₃ with Ni complex led to the isolation of the zwitterionic complex. In norbornene homopolymerization, Ni complexes show very low activity. The addition of B（C₆F₅）₃ to the system led to an up to 4000 fold increase in catalytic activity. Under optimized condition, an activity of up to 1.2× 107g·mol^-1·h^-1 was observed for the zwitterionic Ni complex. Interestingly, the palladium complex was not active at all with or without the addition of B（C₆F₅）₃ under the same conditions. In ethylene homopolymerization, the addition of B（C₆F₅）₃ led to an increase in activity and decrease in molecular weight, which is probably due to the removal of electron density from the nickel center upon B（C₆F₅）₃ binding. In ethylene-norbornene copolymerization, complex showed good activity with up to 10.1% of norbornene incorporation. Interestingly, an decrease in activity was observed upon B（C₆F₅）₃ addition.3. Finally, by taking advantage of several designing strategies, high performance phosphine sulfonate nickel catalysts were designed and prepared by the installation of sterically bulky substituents on the metal axial and ligand ortho positions, as well as the installation of substituents with different electronic properties and labile coordinating base. These nickel catalysts showed high activity and high thermal stability, affording high molecular weight polyethylene. Most importantly, high molecular weight copolymer could be generated from the copolymerization of ethylene with a variety of polar monomers.