Olefin Polymerization with Single Component Organoscandium and Organoyttrium Catalysts

Burger, Barbara J.; Cotter, W. Donald; Coughlin, E. Bryan; Chacon, Stephanie T.; Hajela, Sharad; Herzog, Timothy A.; Köhn, R.; Mitchell, Jonathan Paul; Piers, Warren E.; Shapiro, Pamela J.; Bercaw, John E.

doi:10.1007/978-3-642-79136-9_17

Cited by 15 publications

(13 citation statements)

References 36 publications

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“…In fact, similar observations have been made on a number of other semicrystalline polymers, including some flexible polymers and some semi-stiff polymers. 102 A. Razavi Supaphol et al [216][217][218] reviewed a number of hypotheses that have been proposed to explain the occurrence of multiple melting endotherm phenomena.…”

Section: Thermal Properties and The Origin Of Multiple Meltingmentioning

confidence: 98%

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: Thermal Properties and The Origin Of Multiple Meltingmentioning

confidence: 98%

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

Razavi¹

2013

Advances in Polymer Science

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“…A kinetic isotope effect (KIE) of ∼1.4 for β-CH 3 /β-CD 3 elimination in the products was observed regardless of the ligand (Scheme ). A more important observation is that the KIE of 1.4 is consistent with previous KIE studies probing the α-agostic interaction during olefin insertion into M–R bonds. − Hence, agostic interactions contribute equally to β- Me elimination and its microscopic reverse, olefin insertion, suggesting that the transition state is halfway along the reaction coordinate (Scheme b).…”

Section: β-Me Elimination Within Metallocene Olefin Polymerization Ca...mentioning

confidence: 99%

β-Alkyl Elimination: Fundamental Principles and Some Applications

2016

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This review describes organometallic compounds and materials that are capable of mediating a rarely encountered but fundamentally important reaction: β-alkyl elimination at the metal-Cα-Cβ-R moiety, in which an alkyl group attached to the Cβ atom is transferred to the metal or to a coordinated substrate. The objectives of this review are to provide a cohesive fundamental understanding of β-alkyl-elimination reactions and to highlight its applications in olefin polymerization, alkane hydrogenolysis, depolymerization of branched polymers, ring-opening polymerization of cycloalkanes, and other useful organic reactions. To provide a coherent understanding of the β-alkyl elimination reaction, special attention is given to conditions and strategies used to facilitate β-alkyl-elimination/transfer events in metal-catalyzed olefin polymerization, which provide the well-studied examples.

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“…Agostic interactions are of general interest in organometallic chemistry since they often lead to C−H activation. , Concerning polymerization catalysts, it has been proposed that an understanding of the factors which control β-agostic interactions will yield better control of catalyst activity and polymer molecular weights. − The α-agostic interaction is of particular interest since it might dramatically lower the activation barrier to olefin insertion and influence the stereochemical outcome of the olefin insertion step. − Brintzinger has proposed that an α-agostic interaction rigidifies the transition state of a C 2 -symmetric catalyst undergoing propylene insertion, thereby increasing the isotacticity of the resulting polypropylene (Figure ). , Specifically, the α-agostic interaction firmly orients the polymer chain into the open sector of the catalyst structure to minimize interactions between the alkyl substituent of the monomer and the ligand/polymer array during olefin insertion. In addition, Guerra has proposed that the high syndiospecificity of C s -symmetric catalystsfor propylene polymerization results from a γ-agostic structure which persists in the catalytic species after olefin insertion .…”

Section: Introductionmentioning

confidence: 99%

“…In this study it was concluded that, for the system examined, there was not a significant effect due to an α-agostic interaction on either the rate or stereochemistry of olefin insertion, thus ruling out the modified Green−Rooney mechanism. Also, a substantial amount of evidence presently available (X-ray, IR, NMR) 15,16 indicates that β-agostic ,,,,, (not α-agostic) structures characterize ground states for this class of catalysts.…”

Section: Introductionmentioning

confidence: 99%

α-Agostic Interactions and Olefin Insertion in Metallocene Polymerization Catalysts

1996

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Robert H. Grubbs was born near Possum Trot, KY, in 1942. He received his B.A. and M.S. degrees from the University of Florida working with M. Battiste and his Ph.D. from Columbia University for work with Ronald Breslow. After a postdoctoral year with James P. Collman at Stanford he joined the faculty at Michigan State University in 1969. In 1978 he moved to the California Institute of Technology, where he is now the Victor and Elizabeth Atkins Professor of Chemistry. Geoffrey W. Coates was born in 1966 in Evansville, IN. He obtained a B.A. degree in chemistry from Wabash College in 1989 working with Roy G. Miller and a Ph.D. in organic chemistry from Stanford University in 1994. His thesis work, under the direction of Robert M. Waymouth, investigated the stereoselectivity of metallocene-based Ziegler−Natta catalysts. He is currently a NSF postdoctoral fellow with Robert Grubbs at the California Institute of Technology.

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Olefin Polymerization with Single Component Organoscandium and Organoyttrium Catalysts

Cited by 15 publications

References 36 publications

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

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

β-Alkyl Elimination: Fundamental Principles and Some Applications

α-Agostic Interactions and Olefin Insertion in Metallocene Polymerization Catalysts

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