SiO₂-Supported Anilinoquinone-Based Nickel Catalyzed Copolymerization Of Ethylene And Polar Monomers

Since the discover of Pd(II)and Ni(II)catalysts based on ɑ-diimine ligand,much attention has been received to the development of late transition metal catalysts for olefins polymerization in academia and industry due to their easy synthesis,stability,and high thermal stability.Most importantly,late transition catalysts can initiate directly copolymerization of olefins and polar monomers.However,the control of the particle morphology of resulting polymers and the reactor fouling are the serious limitation of the homogeneous olefin polymerization catalysts for industrial application.In this thesis,aiming at high performance solid supported nickel catalysts(heterogeneous catalysts),anilinoquinone-based nickel catalysts were heterogenized by using silica-supported modified methylaluminoxane(MMAO/Si O2)to investigate the copolymerization behavior of ethylene and polar comonomers.First,the anilinonaphthoquinone-based nickel complexes(cat.1: 4-methyl-2,6-bisbenzhydrylamine;cat.2: 2,6-diisopropylaniline;cat.3 : 2,6-dimethoxyaniline)were employed in homo-and copolymerization of ethylene with polar monomers activated by MMAO/Si O2.Compared with the homogeneous systems,the heterogeneous systems showed improved performances.The heterogeneous system showed higher activity in ethylene polymerization to yield higher molecular weight polyethylene.The activity of cat.1-MMAO/Si O2(5200 kg polymer/(mol Ni·h))and the Mn of resulting polyethylene(27.3×104 g/mol)were twice as much as in the corresponding homogeneous system.Cat.1-MMAO/Si O2 system still kept high activity in ethylene polymerization and copolymerization with 5-hexenyl acetate(HAc)even at high polymerization temperature(3600 kg PE/(mol Ni·h)at 100 oC and 1200 kg copolymer/(mol Ni·h)at 80 oC),indicating high thermal stability of our heterogeneous nickel catalyst.Cat.1-MMAO/Si O2 containing bulky dibezhydrylaniline ligand exhibited unique abilities for ethylene/HAc copolymerization with high activity of up to 4700 kg polymer/(mol Ni·h),producing ethylene/HAc copolymers with Mn value of 10.80×104 g/mol and HAc incorporation of 0.94 mol %.The homogeneous cat.2 cannot initiate ethylene/HAc copolymerization,while the heterogeneous cat.2 can initiate copolymerization of ethylene/HAc efficiently(activity up to 3800 kg polymer/(mol Ni·h)),indicating that the heterogeneous catalysts greatly increase the tolerance of nickel complexes towards the polar functional groups.Cat.1-MMAO/Si O2 bearing sterically bulky substituent showed better thermal stability and tolerance to polar monomers,while cat.2-MMAO/Si O2 and cat.3-MMAO/Si O2 cannot conduct the copolymerization of ethylene/HAc at high polymerization temperatures.Second,we heterogenized the 2,6-diisopropylaniline-anthraquinone nickel complex(cat.4),which is effective in ethylene oligomerization to investigate ethylene(co)polymerization performance.Although the activity of the heterogeneous cat.4-MMAO/Si O2 was much lower than that of the homogeneous system in ethylene homopolymerization,the polymerization product was high molecular weight polyethylene(Mn = 16.00×104 g/mol).The result indicated that the electronic effect of MMAO/Si O2 plays an important role in the polymerization to reduce the chain transfer reaction.Cat.4-MMAO/Si O2 can also promote the copolymerization of ethylene/HAc with moderate activity of 350 kg polymer/(mol Ni·h)to produce the copolymers with Mn value of 2.79×104 g/mol and HAc incorporation of 0.24 mol %.In this thesis,the effects of Si O2 supported zwitterionic nickel complexes in ethylene polymerization and copolymerization with polar monomers were discussed.The future work is mainly focusing on the industrial application of our nickel catalysts.