Density Functional Theory Studyt On The Ethylene And Norbornene Copolymerization Catalyzed By ?-Diimine Ni(?) Complex

The excellent performance of ethylene-norbornene copolymer is current research focus in application of olefin polymerization.More and more researchers start to focus on the low oxygen sensitivity,low cost and adjustable molecular topology of later transition metal catalyst comparing to the traditional metallocene catalyst.This work studied ethylene/norbornene random copolymerization by ?-diimine nickel catalyst system catalyzed.The experimental results showed that ?-diimine nickel catalyst system of traditional Brookhart type can catalyze ethylene homopolymerization and norbornene homopolymerization,but it can't catalyze ethylene/norbornene random copolymerization.Hence we used the computational chemistry method to study kinetics energy of ethylene/norbornene random copolymerization by ?-diimine nickel catalyst system catalyzed for exploring the reasons why copolymerization can't occur.The specific results were as follows:1.Producing the ?-diimine nickel catalyst system of traditional Brookhart type(Catalyst A)and the ?-diimine nickel catalyst(Catalyst B)with large steric hindrance in carbon skeleton structure space.We used separately the Catalyst A and Catalyst B to catalyze ethylene/norbornene homopolymerization and random copolymerization.The results show that they can catalyst ethylene/norbornene homopolymerization but can't catalyze ethylene/norbornene copolymerization,so we used the gas chromatograph-mass spectrometer to analyze the terminated liquid of copolymerization,and found that the main components were monomers and solvents.2.Studying ethylene/norbornene copolymerization by Catalyst A catalyzed,used GaussView software to build the molecular structure of chain initiation,and used Gaussian software to calculate kinetic energy of chain initiation.The study found that the total barrier of norbornene initiation is lower than ethylene initiation.3.For monomer reinsertion,using GaussView software to build the molecular structure of reinsertion,using Gaussian software to calculate kinetic energy of reinsertion.The study found that the total barrier of ethylene reinsertion is lower than norbornene reinsertion.In other words,the ethylene continuous insertion is more likely to occur than the norbornene continuous insertion.We speculated that the larger steric hindrance of norbornene impeded norbornene continuous insertion reaction.4.Using GaussView software to build the molecular structure of ethylene linear chain propagation and ?-hydride transfer reaction and used Gaussian software to calculate kinetic energy of the above reactions.The dynamics results show that the ?-hydride transfer reaction has lower reaction barrier in comparison to the ethylene linear propagation.The reaction rate of ?-hydride transfer reaction is bigger than ethylene linear propagation.5.Through the above studies,we summarized that the kinetics advantage reaction of this copolymerization: Norbornene initiation,Ethylene reinsertion and ?-hydride transfer reaction.The product,after ?-hydride transfer reaction,still possessed catalytic activity which can catalyze Norbornene initiation.Therefore,the above three kinetics advantage reaction can constitute the circulation system resulting in this catalyst can't catalyzed the ethylene/norbornene random copolymerization which confirmed the experimental results.