Late-Transition Metal Nickel(Ⅱ) Complex Catalysts For Olefin Polymerization

Transition metal catalysts play an important role in the polyolefin industry andlate-transition metal catalyst is an area of great current interest. This paperemphasized on studying late-transition metal complex catalyst systems based on bis-(β-ketonamino)nickel (â…¡) for olefin polymerization by means of changingconditions of polymerization. The functions of cocatalysts, characteristics ofpolymerization behavior, characteristics of polymer structure as well as mechanism ofpolymerization were investigated.The polymerizations of styrene were carried out in toluene solution by using bis(β-ketoamino) nickel (â…¡) complexes as the catalyst precursor andmethylaluminoxane (MAO) as the cocatalys. Both of bis (β-ketoamino)nickel (â…¡)/MAO catalytic systems exhibited higher activity for styrene polymerizations, andcan give moderate molecular weight but relative narrow molecular weight distribution.The obtained polymer was confirmed to be atactic polystyrene. A metal-carboncoordination mechanism was proposed.Both of the nickel(â…¡)/MAO catalytic systems exhibited moderate activity forpolymerization of butyl methylacrylate and produced poly (butyl methylacrylate)with high molecular weight and relatively broad molecular weight distribution. Stericbulk and electronic effects of the ligand affect the activation of the catalysts forpolymerization. Electronic effect were more effective than steric bulk effect forpolymerization of butyl methylacrylate.The bis-(β-ketoamino) nickel(â…¡)complexes, as precursor of catalyst, incombination with co-catalyst B(C₆F₅)₃ were determined to have very high activitiesin polymerization of norbornene, and to provide high molecular weightpolynorbornenes with relative moderate molecular weight distribution. Thepolymerization activities and polymerization yields are higher than that of the activeNi(â…¡)-based catalyst after activation with MAO reported previously.