Study On Synthesis And Ethylene Polymerization Catalytic Performance Of A New α-diimine Nickel Catalyst

This thesis mainly focuses on the design and synthesis of the a-diimine nickel(II)complexes for the ethylene polymerization.To enhance the activity and thermal stability of the a-diimine nickel(Ⅱ)complexes,we introduced steric hindered benzhydryl substituted group and electron withdrawing F group.The catalytic property of the new complexes toward ethylene polymerization and the relationships between polymerization conditions and the properties of resultant polyethylenes such as Mw,PDI(polydispersity)and branching content was systematically studied.For changing the steric hindrance and electric effect around the active center through varied substituents on the imino-aryl groups,the microstructure of obtained polymers could be controlled.The polyolefin elastomer(POE)was obtained through the α-diimine nickel complexes and developing a new kind of catalysts which is low cost and efficient for the prepare of POE.These novel ligands and complexes were designed,synthesized,and characterized by NMR,FT-IR and elemental analysis,etc.Upon activation with co-catalysts,their catalytic behaviors for ethylene polymerization were discussed in detail and the mechanical properties of obtained polyethylenes were investigated to evaluate their application performance.Three parts are included in this thesis as follows:Chapter Ⅰ:The background and significance of this research are presented in this part.The research progress and development of polyethylene catalysts and polyolefin elastomers(POE)are reviewed,especially the late-transition metal nickel(Ⅱ)complexes are introduced in detail.Chapter Ⅱ:1-[2,4,6-tris(bis(4-fluorophenyl)methyl)phenylimino]-2-(arylimino)acenaphthylene ligands and corresponding nickel complexes were designed,synthesized,and characterized.Upon activation with co-catalyst MAO and Et2AlCl,these nickel complexes achieved high activities up to 1.29 × 107 g of PE(mol of Ni)-1 h-1 with good thermostability towards ethylene polymerization up to 1.36 × 106 g of PE(mol of Ni)-1 h-1 at 90℃,which achieved the design purpose of the experimental program.DSC test results showed that the melting point of the polyethylene samples were almost lower than 80℃,indicating that the obtained polyethylenes were highly branched.According to 13C NMR measurements,the obtained polyethylenes possessed diversified branches more than 100 branches per 1000(C),especially the short branches,consistent with features of polyethylene elastomer(POE).Mechanical properties tests of the polyethylenes including stress-strain test and stress-strain recovery test showed that these highly branched polyethylenes exhibit good tensile strength and elastic recovery properties which resemble to thermoplastic elastomers(TPEs).Chapter Ⅲ:Systematically summarized the catalytic performance of the catalyst system,these nickel complexes exhibit high activity towards ethylene polymerization and effective in producing high molecular weight and highly-branched polyethylenes for obtaining polyolefin elastomer(POE).It is not necessary to add expensive a-olefin to adjust the branched structure of the polymer,and a high value-added polyolefin elastomer was prepared by using an inexpensive ethylene monomer,which is low in cost and high in efficiency,and has great industrial application prospects.