Die stereospezifische Polymerisation von Propylen: Ein Überblick 25 Jahre nach ihrer Entdeckung

Pino, P.; Mülhaupt, Rolf

doi:10.1002/ange.19800921104

Cited by 69 publications

(13 citation statements)

References 80 publications

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“…The polymerization mechanism involving the face-selective coordination of propylene, its activation, insertion, and stereoselective propagation at a C 2 symmetric active metal center could satisfactorily explain the formation of i-PP with these metallocene-based catalysts according to the same mechanism, and in a similar way, as proposed much earlier for the heterogeneous titanium trichloride-based ZN catalyst systems. With the exception of some minor differences, the enantio-and stereoselectivity as well as regioselectivity of the poly-insertion reaction and chain termination path ways were very similar to those processes that had been proposed for heterogeneous ZN catalysts [64][65][66][67][68][69][70][71][72][73][74][75][76]. What was unprecedented in the polymerization behavior of the newly discovered catalyst systems, however, was the fact that an initially nonchiral metallocene (prochiral!)…”

Section: Bridged Cyclopentadienyl-fluorenyl Metallocene Moleculesmentioning

confidence: 88%

“…9, top). These types of stereo-errors have been detected and were explained in connection with isotactic polymers prepared with the classical TiCl 3 -based ZN catalyst systems [56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76]. They are also ubiquitous in the backbone of the i-PP formed with isotactic-specific metallocene catalysts.…”

Section: Syndiospecific Transition State Structure and Syndio-insertimentioning

confidence: 98%

“…Since the η 5 -bonded aromatic ligands are tied together by a structural bridge and their rearrangement is impossible and excluded, such a reversible interconversion can take place only when the alkyl group (polymer chain) and the coordinating monomer exchange their positions uninterruptedly and systematically after each insertion; i.e., chain migratory insertion! [64][65][66][67][68][69][70][71][72][73][74][75][76]. 7.…”

Section: Mechanism Of Syndiospecific Polymerizationmentioning

confidence: 99%

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Syndiotactic Polypropylene: Discovery, Development, and Industrialization via Bridged Metallocene Catalysts

Razavi¹

2013

Advances in Polymer Science

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This chapter covers the discovery that enabled, for the first time, the manufacturing of high molecular weight, highly stereoregular syndiotactic polypropylene polymers with narrow molecular weight distribution via the new class of metallocene molecules with bridged cyclopentadienyl-fluorenyl ligands. First, the salient crystal structural features of the neutral metallocene molecules and the crystal structure of the corresponding mono-alkyl-zirconocenium cation is introduced. Then, by employing the structural and geometrical data, a realistic working model for the active site precursor is developed and presented. The stereochemistry of the catalytic propylene poly-insertion reaction and the formation of syndiotactic polypropylene according to the enantiomorphic site control mechanism at the enantiotopic cationic active sites, formed after the activation of the prochiral metallocene dichloride with methylaluminoxane, MAO, is reviewed and further delineated. In the following sections, the impact of the introduction of substituents with proper size and composition at some selected positions of the ligand is discussed and the methods for increasing the molecular weight and stereoregularity of syndiotactic polypropylene polymers are elaborated. With the aid of computational calculations on real and hypothetical catalyst systems with substitutionally altered ligand structures, it is shown that the degree of enantioselectivity of syndiospecific catalyst systems can be determined and/or predicted for these systems quantitatively and with high precision. The calculations confirm that the introduction of substituent(s) reinforcing the preferential conformational orientation of the polymer chain enhances the overall enantioselectivity of the active site, and to certain extends stereoselectivity in general, by affecting the site epimerization processes. The computational calculations reveal that to account correctly for the frequency of the site epimerization-dependent m-type stereo-errors it is essential to include the counter-ion, as an integrated part of the A. Razavi (*) 35 Domaine de la Brisee, 7034 Obourg, Belgium e-mail: abbasrazavi@skynet.be catalyst system, into the calculations. The relevance of the symmetry and stereorigidity of the metallocene structure for the syndiospecificity of the final catalyst is debated by presenting a few "non-conforming" catalyst examples.Finally, the challenges involved in the manufacture of syndiotactic polypropylene in commercial scale continuous production processes are highlighted as well as the polymer's unique structural, physical, mechanical and rheological properties.

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Section: Bridged Cyclopentadienyl-fluorenyl Metallocene Moleculesmentioning

confidence: 88%

Section: Syndiospecific Transition State Structure and Syndio-insertimentioning

confidence: 98%

Section: Mechanism Of Syndiospecific Polymerizationmentioning

confidence: 99%

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Syndiotactic Polypropylene: Discovery, Development, and Industrialization via Bridged Metallocene Catalysts

Razavi¹

2013

Advances in Polymer Science

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“…But for the first time, we were able to polymerize propylene with a soluble biscyclopentadienyl-titanium catalyst to obtain atactic polypropylene and to generate ethylene-propylene copolymers. Pino and Mülhaupt, 26 who analyzed a sample, found that the polypropylene synthesized with this catalyst was the purest atactic PP they had ever seen.…”

Section: The Discoverymentioning

confidence: 95%

The discovery of metallocene catalysts and their present state of the art

Kaminsky

2004

J. Polym. Sci. A Polym. Chem.

353

221

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Metallocene and other transition metal complexes activated by methylaluminoxane are highly active catalysts for the polymerization of olefins, diolefins, and styrene, which was discovered at the University of Hamburg about 25 years ago. These catalysts allow the synthesis of polymers with a highly defined microstructure, tacticity, and stereoregularity, as well as new copolymers with superior properties such as film clarity, tensile strength, and lower extractables. A better understanding of the mechanism of olefin polymerization leads to findings of other new single site catalysts. The development of the metallocene/MAO-catalysts from their discovery to their present state of the art is presented. Keywords:metallocene catalysts; methylaluminoxane; olefin polymerization; zirconocene complexes; polyolefins; single site catalysis Dr. Kaminsky received his Ph.D. and degree in chemistry from Hamburg University, Germany in 1971 for investigating the side reactions of biscyclopentadienyl-zirconiumdichloride and triethylaluminum. He then served as lecturer and continued his research on the determination of zirconocene/aluminumalkyl-complexes and recycling of polymers by pyrolysis in a fluidized bed process. During that time he and Hansjörg Sinn discovered that the activity of metallocenes and other transition metals can be increased extremely by the addition of MAO as a cocatalyst. In 1979 he became full professor at the University of Hamburg for Technical and Macromolecular Chemistry and has served as director, dean, and president of German chemical society, Hamburg section. Dr. Kaminsky has received the following honors and rewards: elected to the

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“…Such catalyst systems were extraordinarily effective both in the polymerization of ethylene into high-density polyethylene and of propylene into atactic polypropylene. [6,7] Striking in this cocatalysis, however, is the necessity of employing an extreme excess of MAO (10 2 -10 3 times the metallocene equivalent) to attain such enhanced activity. It is this aspect of its cocatalytic activity that may be termed the MAO conundrum.…”

Section: Introductionmentioning

confidence: 99%

The Extraordinary Cocatalytic Action of Polymethylaluminoxane (MAO) in the Polymerization of Terminal Olefins by Metallocenes: Chemical Change in the Group 4 Metallocene Dimethyl Derivatives Induced by MAO

et al. 2005

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Keywords: Polymethylaluminoxane (MAO) / Group 4 metallocene derivatives / Olefin polymerization / Cocatalysis / Transfer-epimetallationIn the polymerization of olefins with Group 4 metallocene dichlorides or dimethyl derivatives as procatalysts the use of polymethylaluminoxane (MAO) as the cocatalyst, especially in extreme excess (10 2 -10 3 times the metallocene equivalent), has been shown to have an extraordinary accelerating effect on the rate of olefin polymerization, when compared with the cocatalytic action of alkylaluminum halides. In attempts at explaining the greatly superior catalytic activity of MAO in olefin polymerization (the MAO conundrum), hypotheses have generally paralleled the steps involved in the cocatalytic action of R n AlCl 3-n , namely the alkylation of , with greater (Ti) or lesser (Zr) ease, because an alkyne such as diphenylacetylene was then found to insert into the M t -CH 3 bond stereoselectively. In striking contrast, treatment of each metallocene with MAO gave two reactions very different from MeAlCl 2 , namely a steady evolution of methane gas upon mixing and a finding upon hydrolytic workup that the diphenylacetylene present had undergone no insertion into the M t -CH 3 bond but instead had been reductively dimerized completely to (E,E)-1,2,3,4-tetraphenyl-1,3-butadiene. To account for this astonishing difference in chemical behavior between MAO and MeAlCl 2 in their cocatalytic activation of Group 4 metallocenes to olefin polymerization, it is

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Die stereospezifische Polymerisation von Propylen: Ein Überblick 25 Jahre nach ihrer Entdeckung

Cited by 69 publications

References 80 publications

Syndiotactic Polypropylene: Discovery, Development, and Industrialization via Bridged Metallocene Catalysts

Syndiotactic Polypropylene: Discovery, Development, and Industrialization via Bridged Metallocene Catalysts

The discovery of metallocene catalysts and their present state of the art

The Extraordinary Cocatalytic Action of Polymethylaluminoxane (MAO) in the Polymerization of Terminal Olefins by Metallocenes: Chemical Change in the Group 4 Metallocene Dimethyl Derivatives Induced by MAO

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