Branched Polyethylene Prepared by Asymmetric Metallocene [Me_2C(Cp)(Ind)]ZrCl_2
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Branched polyethylene has been prepared by using asymmetric metallocene and MAO catalytic system. By changing the conditions of polymerization, such as temperature, catalyst concentration and the ratio of c (Al)/c ( Zr) , the influence on catalytic activity and polymerization kinetic curve has been revealed. The probable mechanism for forming the branched polyethylene is also discussed.Keywords:
Post-metallocene catalyst
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Cyclopentadienyl complex
Biphenyl
Olefin polymerization
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[Me2C(Cp) (Ind)]ZrCl2 metallocene catalyst has been prepared and employed in a study of ethene polymerization in the presence of the cocatalyst methylaluminoxane. C1 and C2 signals are detected in the 13C NMR spectra of the resultant polymers; this reveals that the resultant polymer is a branched polyethene (polyethylene). The influence of polymerization temperature, catalyst concentration and [Al]/[Zr] ratio on catalytic activities and polymerization kinetics is investigated. A plausible mechanism for forming branched polyethene is suggested. © 2000 Society of Chemical Industry
Methylaluminoxane
Post-metallocene catalyst
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The polymerized metallocene catalyst 4 was prepared by the co-polymerization of ansa-zirconocene complex [ CH3Si (2)]ZrCl2 (3) containing vinyl substituted silane bridge with styrene in the presence of radical initiator. Catalyst 4 was found to display high ethylene polymerization activity of 2.28 x 10(6) g PE/(mol . h) with a viscosity average molecular weight (M-eta) value of 61.6 x 10(3) using methylalumoxane (MAO) as a co-catalyst. The ethylene polymerization has been investigated under different conditions.
Post-metallocene catalyst
Coordination polymerization
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[(N-1-naphthylimino-N’-2, 6-isopropylphenylimino)acenaphthene] dichloronickel (Ⅱ) was prepared and supported on SiO_ 2 /MgCl_ 2 to afford a supported catalyst. With general alkylaluminium as cocatalyst, this supported catalyst was used for ethylene polymerization to produce branched polyethylene. The results show that the polymerization conditions have pronounced influence on catalytic activity and properties of polymerization. When AlEt_ 2 Cl was used as cocatalyst, the catalyst is high active for ethylene polymerization, producing branching polyethylenes with 31.2~62.5 branchers per 1000 carbon atoms. Branching degree of polyethylene increase correspondingly. When the polymerization temperature was 25 ℃ and Al/Ni molar ratio 80 , the supported catalyst achieved highest activity of 5.2×10 5 g PE(molNi·h) -1 .
Branching (polymer chemistry)
Coordination polymerization
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Post-metallocene catalyst
Coordination polymerization
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An alternative route was investigated to prepare linear lower density polyethylene with a single monomer,ethylene,and a dual functional catalytic system for ethylene polymerization in situ using Ti(O n Bu) 4/AlEt 3 as dimerization catalyst and supported metallocene as its copolymerization catalyst.The two catalysts were well matched in a single reactor and the short branched polyethylene made from this catalytic system had the characteristics of low melting point,low density,high activity and proper\|granule morphology of polyethylene.
Linear low-density polyethylene
Post-metallocene catalyst
Low-density polyethylene
Coordination polymerization
Ziegler–Natta catalyst
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Polyethylene with broad molecular weight distribution can be obtained by using catalytic systems consisting of two or more catalyst components. An asymmetrically bridged metallocene compound [(CH 3) 2C(η-C 5H 4)(η-C 9H 6)]ZrCl 2 and different unbridged metallocene compounds( Cp) 2ZrCl 2,( Cp) 2ZrCl 2 and ( [ZJZS;ZX;LX,Y] Cp) 2ZrCl 2 were used to constitute three catalytic systems cocatalyzed with MAO for ethylene polymerization.Polyethylene with short chain branch and broad molecular weight distribution was obtained.By changing the molar ratio of two-component metallocene catalysts and polymerization temperature,the activity of the ethylene polymerization and the molecular weight and molecular weight distribution of the resultant polyethylene were investigated.The molecular weight and molecular weight distribution of polyethylene were determined by viscometry and GPC.The melt point and crystallinity of polyethylene samples were determined by DSC.The results showed that the molar ratio and polymerization temperature had important effect on the activity and molecular weight.The results indicated that it was possible to tailor molecular weight and molecular weight distribution by changing the molar ratio of the two-component metallocene catalysts and polymerization temperature in ethylene polymerization with two-component metallocene catalyst systems.
Molar mass distribution
Post-metallocene catalyst
Coordination polymerization
Molar mass
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Ethylene and styrene were copolymerized by using SiO 2/MAO/Et(Ind) 2ZrCl 2 activited with Aluminonane(MAO). When the time of copolymerization was 30 minutes, the temperature of copolymerization was 40 ℃, the radio of Aluminium to Zirconlum was 300, the concentration of supported metallocene was 2.17×10 -6 mol/L, the atactic ES copolymers were produced. The effect of comonomer in the copolymerization was not observed. With the comonomer ratio increased, the catalytic activity, the copolymer properties, such as molecular weight and melting point of the copolymer were decreased.
Comonomer
Post-metallocene catalyst
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Branched polyethylene was synthesized in heptane used as a polymerization medium with monotitanocene catalyst composed of η5-pentamethylcyclopentadienyl tribenzyloxy titanium and modified methylaluminoxane (mMAO) that contained different amounts of residual trimethylaluminum (TMA). The residual TMA more strongly reduced Ti(IV) complexes to Ti(III) and Ti(II) ones, and Ti(IV) active species were suggested to be more effective for ethylene polymerization. Influences of the polymerization temperature and Al/Ti molar ratio on the catalytic activity and the degree of branching, branch length, and molecular weight of polyethylene were investigated. The obtained polymers were confirmed by 13C NMR to be higher molecular weight polyethylene containing significant amounts of isolated ethyl branches, butyl branches, or both. Branched polyethylene was prepared by the in situ copolymerization of ethylene with 1-butene and 1-hexene, which were formed through a proposed mechanism including metallcycloheptane and metallcyclopentane intermediates of Ti(II) species that were produced by the reaction of Ti(IV) complexes with TMA coexisting in mMAO. There was a remarkable increase in the chance of 1-butene being produced from metallcyclopentane of Ti(II) intermediates with an increase in the polymerization temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4258–4263, 2000
Methylaluminoxane
Branching (polymer chemistry)
Coordination polymerization
Heptane
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Study on the polymerization of ethylene with carbon bridged dinuclear metallocene of Ti-Sm and Zr-Sm
It has been synthesized two new dinuclear metallocene complexes ,which were used for ethylene polymerization with MAO as cocatalyst. Detailed study on the effect of polymerization caused by catalyst concentration, molar ratio of /, temperature and time, showed that the catalytic activity of complex 7 is higher than that of the corresponding mononuclear metallocene of Cp_2TiCl_2, while the catalytic activity of complex 5 is lower than that of the corresponding mononuclear metallocene of Cp_2ZrCl_2; The molecular weight (M_η) of polyethylene produced by above two catalyst systems is somewhat decreased, and the molecular weight distribution (MWD) becomes broader. With prolongation of time, the molecular weight of polyethylene obtained by complex 7 decreases, while the molecular weight of polyethylene obtained by complex 5 increases.
Molar mass distribution
Post-metallocene catalyst
Low-density polyethylene
Coordination polymerization
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