Polyethylene and elastomeric polypropylene using alumina‐supported bis(arene) titanium, zirconium, and hafnium catalysts

Tullock, C. W.; Tebbe, F. N.; Mülhaupt, Rolf; Ovenall, Derick W.; Setterquist, Robert A.; Ittel, Steven D.

doi:10.1002/pola.1989.080270916

Cited by 54 publications

(53 citation statements)

References 43 publications

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“…This is in contrast to what is observed on SiO 2-(700) , which yields a neutral species, [(≡SiO)Zr(CH 2 tBu) 3 ]. These results fully explain the difference of reactivities of alumina vs. silica-supported systems: the former is a highly active polymerization catalyst, while the latter is totally inactive [58][59][60][61] …”

Section: Silica-supported Metal Hydridessupporting

confidence: 59%

Stabilizing reactive intermediates through site isolation

Copéret

2009

Pure and Applied Chemistry

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This overview describes the reaction of organometallics with oxide surfaces and the formation of highly reactive species. In the case of silica, the surface can be seen as a large siloxy ligand, which helps to stabilize reactive intermediates through site isolations. This is translated into very highly reactive and stable well-defined alkene metathesis catalysts as well as the formation of hydrides species, which display unusual reactivities toward alkanes (e.g., low-temperature hydrogenolysis and metathesis of alkanes). In the case of alumina, it allows the formation of highly reactive, but stable cationic species or masked carbenic species whose structures are unusual by comparison with molecular chemistry. Scheme 2 (a) Grafting of [Re(≡CtBu)(=CHtBu)(CH 2 tBu) 2 ] on SiO 2-(700) . (b) Proposed model for the greater activity of asymmetric system. Scheme 3 Scheme 6 On alumina GeneralitiesThe surface of alumina is more complex than this of silica. Indeed, in contrast to silica, in which Si is always tetracoordinated and mainly tetrahedral, the Al atoms of the bulk of transition aluminas (γ or δ) are found in two geometries, tetrahedral (Al Td ) or octahedral (Al Oh ) geometries, whose ratio (Al Td /Al Oh ) is ca. 1:3 for γ-Al 2 O 3 . Considering the surface Al atoms, they will therefore have different natures (tri-, tetra-, penta-, or hexacoordinated) depending on the origin of the Al atom (Al Td /Al Oh ) and the level of hydration of the surface. This will in turn induce a variety of Lewis acid (Al V , Al IV , and Al III ) and hydroxyl sites (Al IV -OH, Al V -OH, Al VI -OH as well as µ 2 -and µ 3 -OH; Scheme 8a). The combination of spectroscopic data and computational studies clearly shows that the (1,1,0) surface is the most abundant (ca. 70 %) and contains the OH groups [54,55]. Moreover, while the nature of the OH species is best described by a trihydrated alumina per unit cell, other studies clearly show that there C. COPÉRET © 2009 IUPAC, Pure and Applied Chemistry 81, 585-596 592 Scheme 7 Scheme 8 (a) IR spectrum of the OH region of Al 2 O 3-(500) and the associated OH group assignment. (b) Models of very reactive Lewis acid sites (defects). (c) Reactivity of defect sites with H 2 and CH 4 . Scheme 10 (a) Grafting of MeReO 3 on Al 2 O 3-(500) . (b) Proposed resting states and active sites of MeReO 3 /Al 2 O 3-(500) .

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Section: Silica-supported Metal Hydridessupporting

confidence: 59%

Stabilizing reactive intermediates through site isolation

Copéret

2009

Pure and Applied Chemistry

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“…6,7,[16][17][18] The elastic properties of these polypropylenes are assigned to a block structure of the chain where regular isotactic and irregular atactic sequences are present. [19][20][21] Studies performed on stereoblock isotactic-atactic polypropylenes [22][23][24][25][26][27][28][29][30] confirm the model that regular (isotactic) segments form small, stable crystals, which are randomly distributed in a soft matrix composed of the atactic chain segments. 5,[22][23][24][25][26] The hard elements act as crosslinks and build up the network necessary for the elastic deformation.…”

Section: Introductionmentioning

confidence: 88%

“…[19][20][21] Studies performed on stereoblock isotactic-atactic polypropylenes [22][23][24][25][26][27][28][29][30] confirm the model that regular (isotactic) segments form small, stable crystals, which are randomly distributed in a soft matrix composed of the atactic chain segments. 5,[22][23][24][25][26] The hard elements act as crosslinks and build up the network necessary for the elastic deformation. For amorphous thermoplastic elastomers, such as styrene butadiene copolymers, it is well known that not only the total number of hard segments but also their distribution within the chain determines the mechanical properties.…”

Section: Introductionmentioning

confidence: 88%

Stress‐induced changes in microstructure of a low‐crystalline polypropylene investigated at uniaxial stretching

Böger

Heise

Marti

et al. 2008

J of Applied Polymer Sci

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Novel asymmetric metallocene catalysts lead to low isotactic polypropylenes (iPP) with randomly distributed stereo irregularities. The polypropylenes are low crystalline and show elastic mechanical behavior due to physical crosslinking. The morphology of such iPP, which is responsible for the observed mechanical properties, is still sparsely resolved. In the present work a low isotactic, low crystalline metallocene iPP containing randomly distributed stereoerrors was investigated. The influence of the chain microstructure in the elastic properties was studied using two complementary investigation methods, X-ray diffraction and scanning force microscopy (SFM). For a better understanding of the unique mechanical properties, microscopic changes in morphology and strain-induced variation in chain orientation were monitored during uniaxial stretching using SFM and wide angle X-ray scattering measurements. For quantitative analysis and discussion the polymer chain orientations were calculated. The correlation between the orientation, the arrangements of the amorphous and crystalline phases observed by SFM, and the mechanical properties of the material at different elongation ratios allowed an interpretation of the macroscopic behavior on the microscopic scale. It was shown that the deformation behavior of low isotactic polypropylene with randomly distributed stereoerrors is in agreement with existing structural models, which proposed that small crystalline domains act as physical crosslinks for the amorphous matrix.

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“…Grafting of [Zr(CH 2 tBu) 4 ] on alumina provides an efficient polymerization catalyst, while the same species grafted on silica is inactive [4][5][6][7][8]. By treatment under hydrogen, the grafted Zr-alkyl is a precursor for a surface zirconium hydride which is active in the hydrogenolysis of butane [9].…”

Section: Introductionmentioning

confidence: 99%

“…Silica is a classic choice, generating monosiloxy, bissiloxy and in some cases trissiloxy surface complexes which can be used as catalyst in several reactions (hydrogenation, polymerization, metathesis) [2,3]. In many cases however, other supports such as alumina must be used to yield active surface species [4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Gamma-alumina: An Active Support to Obtain Immobilized Electron Poor Zr Complexes

et al. 2008

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By grafting well-defined metallic complexes on a solid support, surface organometallic chemistry provides a bridge between homogeneous and heterogeneous catalysis. This innovative approach has already proven its efficiency for several reactions: polymerization, olefin and alkane metathesis… However several fundamental questions remain open on the chemical role of the oxide surface, on the grafting mechanism and on the reactivity of the grafted complex. Is a single well-defined surface/metal/ligand complex formed? Is the solid surface just an inert support, or does it play an active chemical role? We combine on the one hand reactivity and spectroscopic experiments with on the other hand total energy calculations and spectra simulations (NMR, IR) in order to propose insights for these open questions, using the example of [Zr(CH 2 tBu) 4 ] complex grafted on partially dehydroxylated gamma-alumina. A molecular level approach to the grafting mechanism is proposed. Alumina plays a dual role, both as support and Lewis acid co-catalyst. The hydroxyl groups permit the covalent grafting through Al-O-Zr linkages, while the neighboring Al Lewis sites allow the formation of an ion pair, by transfer of an alkyl ligand from the Zr toward the Al. The formed cationic Zr center shows an enhanced electrophilic character. The mechanism of the formation of the Zr hydride supported on alumina, upon treatment under H 2 gas is described, with the formation of a mixture of mono-hydride (Zr + -H; Al --CH 2 tBu) and bis-hydride (Zr + -H; Al --H). This Zr hydride supported on alumina is active for butane hydrogenolysis. A mechanism with reasonable energy barriers is proposed, the rate limiting step being the C-C scission.

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Polyethylene and elastomeric polypropylene using alumina‐supported bis(arene) titanium, zirconium, and hafnium catalysts

Cited by 54 publications

References 43 publications

Stabilizing reactive intermediates through site isolation

Stabilizing reactive intermediates through site isolation

Stress‐induced changes in microstructure of a low‐crystalline polypropylene investigated at uniaxial stretching

Gamma-alumina: An Active Support to Obtain Immobilized Electron Poor Zr Complexes

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