Zur Kettenwachstumsgeschwindigkeit der intermittierenden Äthylenpolymerisation

Reichert, Von K. H.

doi:10.1002/apmc.1970.050130113

Cited by 22 publications

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“…A useful concept for the description of these metallocene catalyst systems goes back to the kinetic studies of Reichert's group [79,80]. During the growth of a polymer chain, each metal polymer species appears to alternate between a ''dormant'' state and a state in which it actively grows.…”

Section: Early Soluble Unbridged Metallocene Catalysts In Connection mentioning

confidence: 99%

Polymerization on Molecular Catalysts

Fink

2008

Handbook of Heterogeneous Catalysis

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Section: Early Soluble Unbridged Metallocene Catalysts In Connection mentioning

confidence: 99%

Polymerization on Molecular Catalysts

Fink

2008

Handbook of Heterogeneous Catalysis

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“…Various types of intermediate species and structures were discussed and characterized via different methods. [51,52] Henrici-Olivé and S. Olivé [53,54] discussed an octahedral coordination sphere on the basis of EPR measure-ments. G. Fink [55,56] found tetrahedral coordination by application of enriched 13 C-NMR measurements and fully discussed a polymerization system for the quenched-flow polymerization of Cp 2 TiEtCl as catalyst with AlEtCl 2 as co-catalyst [57][58][59][60] .…”

Section: Ziegler-natta (Zn) Polymerizationmentioning

confidence: 99%

Mechanism and Kinetics of Catalyzed Chain Growth

Primpke¹

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In this work, the activation and polymerization mechanism of Catalyzed Chain Growth (CCG) polymerization of ethylene and styrene was studied. On the basis of two metallocene catalysts (Cp* 2 ZrCl 2 and Cp* 2 NdCl 2 Li(OEt 2 ) 2 ) and dibenzyl magnesium (BzMgBz) and n-butyloctyl magnesium (BuMgOct) as co-catalysts the mechanism was determined via a model reaction and afterwards transferred to a typical CCG system. The model system consisting of Cp* 2 ZrCl 2 and BzMgBz cannot perform β-hydride elimination and was first studied via Nuclear Magnetic Resonance (NMR). A mechanistic scheme was proposed and kinetic coefficients were successfully derived via modeling in PREDICI TM . Data analysis was simplified due to direct calculation of the coefficients from NMR data. The analytical toolbox was extended to Ultra-Violet/Visible (UV/Vis) spectroscopic studies. Based on this method the influence of di-n-butyl ether (DBE) on the catalyst/co-catalyst system was studied and a strong lowering of rate coefficients was found. The co-catalyst was switched to BuMgOct, where β-hydride elimination of the alkyl chains was found to be fast at 70 • C and dominating the activation mechanism. This hinders the system to perform ethylene polymerization. The UV/Vis method was applied to the reaction of Cp* 2 NdCl 2 Li(OEt 2 ) 2 with BzMgBz. Equilibrium constants between a monoalkylated complex and the benzyl brigded bimetallic Nd-Mg complex were determined in dependence of temperature. The reaction turned out to be strongly dependent on the presence of other coordinating molecules like DBE. The activation mechanism of Cp* 2 ZrCl 2 and BzMgBz was successfully utilized for modeling the polymerization of styrene-d8 by NMR studies. It was found that the basic steps of the exchange reactions are similar to those of activation. The model was successfully extended to the introduction of polymeric species, and kinetic parameters were derived. The process of monomer addition was found to be chain-length dependent and the influence of the single rate coefficients on the reaction were screened. It was found that a low catalyst precursor concentration can lead to a rate enhancement. Addition of tetrahydrofurane was found to be disadvantageous for the polymerization reaction. BuMgOct as co-catalyst leads to a process where the termination reaction of the alkyl Scheme 2.2: Transfer reaction scheme for magnesium derivatives. Adapted with permission from S. Bogaert et al. [21] Copyright 2000 WILEY-VCH Verlag GmbH, D-69451 WeinheimIn contrast to neodymium and iron-based catalysts, the chosen Cp * 2 ZrCl 2 (A)/ BzMgBz model system is non-paramagnetic. Initialization is a critical phase during polymerization in CCG. If the chains from the CTA are not transferred fast and the first monomer addition is slow the MMD will be broadened or the process goes over into a CCTP like polymerization. Results of this section were already published in literature [269] .

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Stereospezifische Olefinpolymerisation mit chiralen Metallocenkatalysatoren

et al. 1995

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Untersuchungen an neuen Metallocenkatalysatoren zur Polymerisation von α‐Olefinen haben gegenwärtig weitreichende Auswirkungen auf die Entwicklung neuer Materialien und auch auf unser Verständnis der grundlegenden Reaktionsmechanismen, die für das Wachstum von Polymerketten an einem Katalysatorzentrum und für deren Stereoregularität verantwortlich sind. Im Gegensatz zu heterogenen Ziegler‐Natta‐Katalysatoren erfolgt die Polymerisation mit einem homogenen Metallocenkatalysator im Prinzip an einheitlichen Metallzentren mit definierter Koordinationssphäre. Dies macht es möglich, die Struktur der Metallocenkomplexe mit den Eigenschaften des Polymers, beispielsweise Molekulargewicht, stereochemischer Mikrostruktur, Kristallisationsverhalten und mechanischen Eigenschaften, zu korrelieren. Mit homogenen Katalysatorsystemen können Regio‐ und Stereoregularitäten, Molekulargewichte, Molekulargewichte, Molekulargewichtsverteilungen und Einbauverhältnisse von Comonomeren wirksam kontrolliert werden. Diese Katalysatoren eröffnen neue Zugänge zur Homo‐ und Copolymerisation cyclischer Olefine, zur Cyclopolymerisation von Dienen und sogar zu funktionalisierten Polyolefinen und erweitern somit das Spektrum und die Vielseitigkeit technisch verfügbarer Polyolefin‐Materialien.

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Zur Kettenwachstumsgeschwindigkeit der intermittierenden Äthylenpolymerisation

Abstract: SUMMARY:A general method to determine the propagation rate constant of slow polyreactions is described. By this method it can be shown that the active species of the coordinative polyremtion of ethylene by the soluble ZIEQLER-NATTA-CatttalySt

Cited by 22 publications

References 1 publication

Polymerization on Molecular Catalysts

Polymerization on Molecular Catalysts

Mechanism and Kinetics of Catalyzed Chain Growth

Stereospezifische Olefinpolymerisation mit chiralen Metallocenkatalysatoren

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