Site selective ligand modification and tactic variation in polypropylene chains produced with metallocene catalysts

Razavi, Abbas; Thewalt, Ulf

doi:10.1016/j.ccr.2005.07.006

Cited by 97 publications

(57 citation statements)

References 51 publications

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“…23. Complex 8 fulfills all symmetry requirements that one would expect a priori from a would-be syndiotactic-specific precatalyst molecule, nevertheless, after its activation with MAO and its exposure to propylene, complex 8 produces polypropylene chains with perfectly atactic microstructure [28,30].…”

Section: Syndio-and Nonsyndiospecific Catalyst Systems With C S Symmementioning

confidence: 94%

“…Figure 14 shows the hydrogenation scheme for the two metallocene complexes 1 and 6 and the formation 68 A. Razavi of the complex, diphenylmethylidene-μ-(cyclopentadienyl-octahydrofluorenyl)ZrCl 2 , 8, as the only hydrogenation product. Metallocene 8 was obtained from 6 under mild hydrogenation conditions [28,30]. All attempts to hydrogenate metallocene 1 under similar and even more vigorous conditions failed.…”

Section: Polymerization Behavior Of Diphenylmethylidene (Cyclopentadimentioning

confidence: 99%

“…Catalyst prepared with the complex 9/MAO is more active than the corresponding catalysts prepared with complexes 1 and 6 under the same polymerization conditions. Tables 7 and 8 present the polymerization conditions, results, and polymer analyses of the syndiotactic polymers produced with the 9/MAO catalyst system at different polymerization temperatures [28][29][30]. A quick comparative 70 A. Razavi glance at the data given in Tables 1, 2, 7, and 8 reveals that the introduction of tertbutyl groups in positions 3 and 6 of the fluorenyl moiety of the ligand causes substantial improvements with respect to enantio-and stereoselectivity of the resulting catalysts 9/MAO and the stereoregularity of the s-PP polymers it produces.…”

Section: Stereoregularity Improvement and Frontal Substituentsmentioning

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: Syndio-and Nonsyndiospecific Catalyst Systems With C S Symmementioning

confidence: 94%

Section: Polymerization Behavior Of Diphenylmethylidene (Cyclopentadimentioning

confidence: 99%

Section: Stereoregularity Improvement and Frontal Substituentsmentioning

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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“…3) [13][14][15]. This highly active homogeneous system allows for tuning of the product polymer microstructure (M w , PDI, % comonomer incorporation, tacticity) exclusively by varying the organic ancillary ligands surrounding the group 4 metal [14,[16][17][18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

“…Especially in the case of group 4, these new catalysts and cocatalyst/activators have achieved great success in the production of advanced polyolefin materials [4]. The new systems are able to control product molecular weight, polydispersity, comonomer enchainment level and pattern, the tacticity of poly(a-olefins) [17,56,57], copolymerization of olefins with polar comonomers (group 10) [54,55,[58][59][60][61][62], and the catalytic synthesis of block copolymers by processes such as chain shuttling polymerization [63][64][65][66][67].…”

Section: Introductionmentioning

confidence: 99%

Supported Single-Site Organometallic Catalysts for the Synthesis of High-Performance Polyolefins

2014

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Single-site organometallic catalysts supported on solid inorganic or organic substrates are making an important contribution to heterogeneous catalysis. Early and late transition metal single-site catalysts have changed the polyolefin manufacturing industry and research with their ability to produce polymers with unique properties. Moreover, several of these catalysts have been commercialized on a large scale. Their heterogenization for slurry or gas phase olefin polymerization is important to produce polyolefin as beads and to avoid reactor fouling. The large majority of supports currently used in industry are inorganic materials (SiO 2 , Al 2 O 3 , MgCl 2 ), with silica being the most important. Single-site supported catalysts are most commonly prepared by molecular-level anchoring/chemisorption, in which a molecular precursor undergoes reaction with the surface while maintaining most of the ligand sphere of the parent molecule. Chemisorption of discrete organometallic complexes on solid supports yields catalysts with well-defined active sites, greater thermal stability than the homogeneous analogues, and decreased reactor fouling versus the homogeneous analogues. This review presents a detailed account of the synthesis, characterization and polymerization properties of single-site catalysts supported on metal oxides and metal sulfated oxides, primarily carried out at Northwestern University.

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Metallocene Catalysts

Kaminsky

2015

Kirk-Othmer Encyclopedia of Chemical Technology

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Metallocene catalysts are useful for the polymerization of olefins and copolymerization of ethene or propene with cyclic olefins, styrene, and polar vinyl monomers. These catalysts contain two components such as a metallocene or half‐sandwich complex of transition metals and an organoaluminum compound, methylaluminoxane (MAO), or a perfluorinated boron aromatic compound. Most polymerization active metallocenes contain zirconium or titanium as transition metal but also hafnium, chromium, scandium, or others. The use of metallocene catalysts and their modifications has widely increased the synthetic and technical possibilities in more precisely controlling the polymer composition, polymer structure, tacticity, and other special properties. They allow the synthesis of polyolefins with short‐ or long‐chain branches, different tacticities and stereoregularities, copolymers with high‐compositional uniformity, new norbornene or styrene copolymers, and polyolefin composite materials in a purity that cannot be obtained by Ziegler–Natta catalysts. Today, industries mainly produce metallocene‐based linear low‐density polyethylene (LLDPE) and ethene/propene (EPM and EPDM) copolymers. These polyolefins show a higher growing rate than similar polymers obtained by conventional catalysts. The single‐site character of metallocene/MAO or other metallocene/borate catalysts has led to a better understanding of the mechanism of olefin polymerization.

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Site selective ligand modification and tactic variation in polypropylene chains produced with metallocene catalysts

Cited by 97 publications

References 51 publications

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

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

Supported Single-Site Organometallic Catalysts for the Synthesis of High-Performance Polyolefins

Metallocene Catalysts

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