Short chain-branched polyethylene produced by [(CH3)2C(η-C5H4)(η-C9H6)]ZrCl2 and [(η-C5H4)(η-C9H6)]ZrCl2 metallocene catalyst

Wang, Li; Yue, Yuan; Feng, Linxian; Wang, Youxiang; Ge, Congxin; Ji, Bing

doi:10.1016/s0014-3057(99)00078-6

Cited by 10 publications

(2 citation statements)

References 7 publications

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“…A few evidences have been reported in the literature indicating the presence of some amount of branches in polyethylene produced by homopolymerization with a variety of homogeneous catalysts. The significant formation of about 2 mol % ethyl branches has been recently found by some of us using the meso isomer of the ethylenebis(1-indenyl)zirconium dichloride (EBIZrCl 2 ) while a not specified amount of the same branching was found by Wang et al in polyethylene obtained with other asymmetric zirconocenes. An isomerization mechanism for the ethyl branches formation has been proposed involving β-hydrogen transfer to the incoming monomer.…”

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confidence: 61%

Formation of Quaternary Carbon Centers in Ethylene Polymerization with meso-Isopropylidenebis(1-indenyl)zirconium Dichloride Activated by MAO

et al. 2000

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confidence: 61%

Formation of Quaternary Carbon Centers in Ethylene Polymerization with meso-Isopropylidenebis(1-indenyl)zirconium Dichloride Activated by MAO

et al. 2000

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“…In addition, GC results showed that oligomerization products were mainly even-numbered LAOs (C 6 –C 16 ). Therefore, β-hydrogen transfer was confirmed as the major chain transfer mechanism for ethylene nonselective oligomerization. − Moreover, the FT-IR spectrum of polyethylene product (Figure ) showed the obvious vibrations associated with terminal vinyl groups (ν = 908 and 991 cm –1 ), which also indicated that β-hydrogen transfer was the major chain transfer mechanism for ethylene polymerization. − However, β-hydrogen transfer can occur either (i) to the coordinating ethylene monomer (BHT) or (ii) to the chromium center (β-hydrogen elimination, BHE). In the first case, the M w of the obtained polymer would be independent of ethylene pressure.…”

Section: Results and Discussionmentioning

confidence: 99%

Mechanistic Studies on the Switching from Ethylene Polymerization to Nonselective Oligomerization over the Triphenylsiloxy Chromium(II)/Methylaluminoxane Catalyst

et al. 2015

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Our previous experimental report showed a switching behavior from ethylene polymerization to nonselective oligomerization by a novel triphenylsiloxy complex of chromium(II) [(Ph3SiO)Cr·(THF)]2(μ-OSiPh3)2 (1) together with methylaluminoxane (MAO) as a cocatalyst. In this work, combined experimental and computational studies were carried out to shed some light on the nature of the active species and their fascinating switching mechanism. The experimental results and DFT calculations suggested that (i) the chain propagation and chain transfer processes proceed via a Cossee–Arlman mechanism and β-hydrogen transfer to the chromium center, respectively; (ii) the trivalent cationic model [(Ph3SiO)CrIIIMe]+ and [(η6-toluene)CrIIIMe2]+, which could be generated by a disproportionation reaction, are the most plausible active species for ethylene polymerization, and the divalent cationic model [(η6-toluene)CrIIMe]+ might be responsible for ethylene nonselective oligomerization. A switching mechanism from ethylene polymerization to nonselective oligomerization in the 1/MAO catalyst system was proposed on the basis of DFT calculations. These results may have useful implications for studying active species and the mechanism of transition-metal-catalyzed olefin polymerization and oligomerization.

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Self‐Immobilizing Precatalysts: Norbornene‐Bridged Zirconium ansa‐Metallocenes

et al. 2008

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Abstract:We report here the synthesis of new tethered biscyclopentadienyl and bisindenyl zirconocenes, bearing one unsaturation on the interannular bridge, and their use as self-immobilizing catalysts. They proved to be active catalysts towards ethylene polymerization in solution, with activities comparable to those displayed by commercial rac-Et-A C H T U N G T R E N N U N G (Ind) 2 ZrCl 2 . When tested as self-polymerization catalysts under suitable experimental conditions, they gave colored precipitates that, once reactivated with MAO, were significantly active in ethylene polymerization, although lower than those of the corresponding catalytic systems in solution. The molecular weights of the produced polymers were similar to those obtained with the same catalysts in solution, but their distribution resulted to be broader, with values typical of heterogeneous catalytic systems. From 13 C NMR studies we had the first spectroscopic evidence of the actual incorporation of a metallocene of this type into a polymeric chain.

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Short chain-branched polyethylene produced by [(CH3)2C(η-C5H4)(η-C9H6)]ZrCl2 and [(η-C5H4)(η-C9H6)]ZrCl2 metallocene catalyst

Cited by 10 publications

References 7 publications

Formation of Quaternary Carbon Centers in Ethylene Polymerization with meso-Isopropylidenebis(1-indenyl)zirconium Dichloride Activated by MAO

Formation of Quaternary Carbon Centers in Ethylene Polymerization with meso-Isopropylidenebis(1-indenyl)zirconium Dichloride Activated by MAO

Mechanistic Studies on the Switching from Ethylene Polymerization to Nonselective Oligomerization over the Triphenylsiloxy Chromium(II)/Methylaluminoxane Catalyst

Self‐Immobilizing Precatalysts: Norbornene‐Bridged Zirconium ansa‐Metallocenes

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