Study On Ethylene Polymerization By Late Transitional Fe And Ni Organometallic Catalysts

To date, the researches on late transitional metal catalysts are mainly aimed at mononuclear catalysts. Only a few researches are reported on binuclear late transitional metal catalysts. There is cooperative effect between two metal centers in binuclear polyolefin catalysts, which makes binuclear catalysts display different catalytic performance from correspondent mononuclear catalysts (such as, enhancing catalytic activity and the molecular weight of polymer obtained and broadening the molecular weight distribution). The dissertation systematically studied the influences of modification on binuclear catalyst structures and polymerization conditions on catalytic activity and properties of polymer obtained. The detailed work is as follows:1. Methylene bridged binuclear bis(imino)pyridine iron catalystsThree methylene bridged binuclear bis(imino)pyridine iron complexes({[2,6-R₂-C₆H₃N=C(CH₃)C₅H₃N(CH₃)C=N(3,5-R'₂)C₆H₂-CH₂-(3,5-R'₂)C₆H₂N=C(CH₃)C₅H₃N (CH₃)C=N(2,6 -R₂)C₆H₃][FeCl₂]₂ (R,R'=i-C₃H₇ (Fe4); R=i-C₃H₇, R'=CH₃ (Fe5); R,R'=CH₃ (Fe6))}) have been synthesized. The paramagnetic character of the iron catalyst makes NMR analysis impossible. So fast atom impact (FAB-MS), FT-IR and elemental analysis were used to confirm the binuclear nickel complexes. In addition, three mononuclear bis(imino)pyridine iron complexes ({[ArN=C(Me)C₅H₃N(Me) C=NAr')]FeCl₂ (Ar,Ar'=2,6-C₆H₃-i-Pr (Fel);Ar =2,6-C₆H₃-i-Pr₂, Ar'= 2,6-C₆H₃-Me₂ (Fe2);Ar,Ar'= 2,6-C₆H₃-Me₂(Fe3))}) have been synthesized as comparison. Influences of catalyst structure, polymerization conditions and different cocatalysts on ethylene polymerization were investigated to study the catalytic potential of these binuclear iron catalysts. The PE obtained were characterized by DSC, GPC and ¹³C NMR. It was found that modifying the catalyst structure has a great effect on catalytic activity, PE molecular weight and its distribution. Except for Fe4/Al(i-Bu)3 catalytic system, the other binuclear iron catalytic system displayed higher catalytic activity and produced higher molecular weight PE than their corresponding mononuclear iron catalytic system. The molecular weight distribution of PE produced by binuclear iron catalytic systems is broad, even bimodal.2. Fe(acac)3-bis(imino)pyridine/MAO(Al(i-Bu)3) catalytic systemsIn the presence of MAO, Fe(acac)₃ and bis(imino)pyridine will generate active catalytic species in one pot"(in situ) in which ethylene polymerization takes place. These catalytic systems displayed very high catalytic activity and produced high molecular weight. Effects of catalyst composites, polymerization conditions, addition order etc on the polymerization of ethylene. The PE obtained is characterized by DSC, High Temperature GPC and ¹³C NMR spectrum. The results indicate that the polymer are highly linear and crystalline PE with bimodal molecular weight distribution.L4-L6 systems displayed higher catalytic activity than L1-L3 systems.New catalytic systems formed by Fe(acac)₃, bis(imino)pyridine and Al(i-Bu)₃ were used for the polymerization of ethylene. The influences of key factors, such as reaction temperature and Al/Fe molar ratio, on ethylene polymerization were investigated. It was found that Fe(acac)₃-bis(imino)pyridine/Al(i-Bu)₃ system displayed lower catalytic activity than Fe(acac)₃-bis(imino)pyridine/MAO system. The molecular weight distribution of PE obtained are relatively narrow and in the range 3.54-4.26 due to the absence of chain transfer to Al(i-Bu)₃ reaction.3. Methylene bridged binuclearα-Acenaphthenediimine nickel catalystsThree Methylene bridged binuclearα-Acenaphthenediimine nickel complexes ({[2,6-R2-C₆H₃N=C(C₁₀H₆)C=N-(3,5-R'₂)C₆H₂(CH₂)(3,5-R'₂)C₆H₂-N=C(C₁₀H₆)C=N (2,6-R₂)C₆H₃](NiCl₂)₂ (R,R'=i-C₃H₇ (Ni3); R=i-C₃H₇, R'=CH₃ (Ni4);R,R'=CH₃ (Ni5))}) have been synthesized and characterized by FT-IR, elemental analysis and FAB-MS. In addition, two mononuclearα-Acenaphthenediimine nickel complexes (2,6-(i-Pr)₂C₆H₃-N=C(C₁₀H₅)C=N-2,6-(i-Pr)₂C₆H₃NiCl₂(Ni1) and 2,6-Me₂C₆H₃-N=C (C₁₀H₅)C= N-2,6-Me₂C₆H₃NiCl₂ (Ni2)) have been synthesized as comparison. In the presence of MAO, effects of catalyst structure and polymerization conditions on the catalytic activity of these binuclear nickel complexes, PE molecular weight, molecular weight distribution and PE microstructure. The results indicate that catalyst structure have great influence on catalytic activity and PE microstructure like polymerization conditions. The catalytic: activity and PE molecular weight of these five nickel catalysts obey the order of Ni3>Ni1>Ni2>Ni4>Ni5 and Ni3>Ni4>Ni1>Ni5>Ni2 respectively. Furthermore, tuning catalyst structure and polymerization conditions could control the polymerization of ethylene to give PE with different degree of branches.4. Methylene bridged binuclear neural salicylaldimine nickel catalystsOne binuclear neutral salicylaldimnie nickel complex ({[O-(3-Cyclopentenyl)-(5-Me)C₆H₂-o-C(H)=N-2,6-(i-Pr)₂C₆H₂]₂CH₂}[Ni(Ph₃P)(Ph)]₂) (Ni6) have been synthesized and confirmed by elemental analysis and ¹HNMR. In combination with Ni(COD)₂ as phosphate scavenger, binuclear nickel complex displayed high catalytic activity for the polymerization of ethylene. It is noted to that this binuclear nickel complex is able to catalyze ethylene polymerization as single-component catalyst. It maybe due to that micro-chemical environment around the nickel center were changed by the involvement of methylene bridge into catalyst structure, which makes tri-phenylphosphine group easier to leave, resulting in active species to initiate the polymerization of ethylene.