Olefin Polymerization Behavior Of Neutral Nickel Catalyst

The major catalysts of olefin polymerization most widely used in factories are Ziegler-Natta and metallocene catalysts so far, but both the two systems have a lot of fatal defects respectively. In recent years, there have been many rapid advances in the catalysis of olefin polymerization, including late transition metals. With a single active center, these catalysts have many advantages when compared with classical Ziegler-Natta and metallocene catalysts, and the most important one among them is the lower oxophilicity and presumed greater functional-group tolerance of late transition metals relative to early metals. As a result, late transition metals catalysts are made likely targets for the development of catalysts for the copolymerization of ethylene with polar comonomers under mild conditions, even in aqueous solution, which enlarges the scope of olefin polymerization. Neutral nickel catalysts have become a hot issue in the area, because of their amazing prospect of homopolymerization of olefin and copolymerization of ethylene with polar comonomers. In addition, these catalysts are relatively less sensitive to polar solvent and air, and can copolymerize ethylene with polar comonomers without cocatalyst. It will be undoubtedly an important aspect of development of olefin polymerization catalysts in future. My dissertation includes two major sorts of neutral nickel catalysts: One is a series of fluorinated salicylaldiminato based novel neutral Ni(II) complexes; The other is a kind of novel binuclear Ni(II)-methyl complex bearing 3,3'-bis(salicylaldiminato)-type ligand. A series of novel neutral Ni(II) complexes bearing fluorinated salicylaldiminato ligands were synthesized and characterized. In these catalysts, the strong inductive effect and conjugative effect of the fluorine atom(s), which have a close relationship with positions in the N-aryl moiety of the salicylaldiminato ligand, can bring influence on molecular electron cloud distribution. With MMAO as cocatalyst, these well-defined complexes are highly active towards vinylic polymerization of nobornene, and the highest activity is up to 7.68×107g PNB/molNi?h under optimized conditions, and all polymers display high molecular weights (Mv's up to 840 kg/mol). Much higher activities are observed than unsubstituted complex under the same conditions, and the best modified catalyst has a 70% higher activity than the unsubstituted complex. Research result indicates that the amount and position of the fluorine atom(s) have little impact on activity, but can slightly modulate molecular weights of polymers. Catalyst Activity, polymer yield, and polymer molecular weight can be controlled by variation of the reaction parameters such as reaction temperature, Al/Ni molar ratio and monomer concentration.A kind of novel binuclear Ni(II)-methyl complex bearing 3,3'-bis(salicylaldiminato)-type ligand was synthesized and characterized. Activated by Lewis acid B(C6F5)3, the complex shows the best activity of up to 3.39×105 g PE/molcat?h at 65oC. As a single-component catalyst, the binuclear complex can also polymerize ethylene very effectively under high ethylene pressure. A high activity of up to 2.49×105 g PE/molcat?h is observed when reaction temperature comes up to 90oC, which indicates that the catalyst has more stable properties and a much higher activity than its'counterpart-a binuclear phenyl nickel complex. Polymer molecular weight and molecular weight distribution can be controlled by variation of the reaction parameters.Activated by B(C6F5)3, it is found for the first time that this kind of binuclear Ni(II)-methyl complex has a fairly high activity of up to 4.75×107 g PNB/molcat?h towards vinylic polymerization of nobornene. The polymer microstructure obtained through the method has been proved by 13C NMR to be entirely different from that produced by neutral nickel complex and MMAO system. Primary result of copolymerization of ethylene with nobornene indicates that the copolymerization can be achieved with a high activity of more than 105 g copolymer/molcat?h, and the copolymer containing more than fifty percent of nobornene can be accessible merely by variation of the reaction parameters.