Supported transition metal complexes for ethylene polymerization

Braca, G.; Sbrana, Glauco; Raspolli-Galletti, Anna Maria; Altomare, Angelina; Arribas, Guillermo; Michelotti, Marco; Ciardelli, Francesco

doi:10.1016/1381-1169(95)00167-0

Cited by 25 publications

(9 citation statements)

References 20 publications

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“…The immobilization of metallocene/MAO systems on solid carriers is normally accompanied by a decrease in catalytic activity. The activity drop has been attributed to (1) geometric restrictions of monomer access to the active sites 1,2 or the limitation of metallocene-MAO interaction due to isolated confinement; 3 (2) the deactivation of metal centers during the immobilization, which results in low ratios of activeto-total transition metal centers; 4,5 and (3) a decrease in the propagation rate. 6 Occasionally, supported metallocene/MAO catalysts exhibit higher average activities than homogeneous ones due to more stable kinetic profiles.…”

Section: Introductionmentioning

confidence: 98%

“…6 Occasionally, supported metallocene/MAO catalysts exhibit higher average activities than homogeneous ones due to more stable kinetic profiles. 4 It has long been known that catalyst morphology has a strong influence on the initial fragmentation and, hence, polymerization behavior of supported catalysts. 7,8 McDaniel 9 observed increases in the polymerization activity with increasing porosity of silicasupported chromium and Ziegler-Natta catalysts.…”

Section: Introductionmentioning

confidence: 99%

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Influence of support friability and concentration of α‐olefins on gas‐phase ethylene polymerization over polymer‐supported metallocene/methylaluminoxane catalysts

Hammawa

Wanke

2007

J of Applied Polymer Sci

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The effects of support friability (F) and ethylene/comonomer ratios were investigated over supported metallocene/methylaluminoxane catalysts prepared with nine different porous polymeric supports and various comonomer concentrations with a 2-L reactor operated in the semibatch gas-phase mode at 808C and 1.4 MPa. F of the supports was measured with a newly devised method. The performance of the supported catalysts depended on support F as follows. The average homopolymerization activities varied from less than 6 t of polyethylene (PE) (mol of Zr)À1 h À1 for low-F catalysts to 10-20 t of PE (mol of Zr)À1 h À1 for moderate-F catalysts and up to 100 t of PE (mol of Zr) À1 h À1 for the high-F catalysts. The presence of 1-hexene and propylene comonomers increased the activity of the low-F catalysts by up to 20-fold and 50-fold, respectively; that is, there were very marked comonomer effects. Activity enhancement by 1-hexene was less than 3-fold for the moderate-F catalysts, whereas the high-F catalysts showed little activity enhancement. Sometimes, 1-hexene even resulted in activity reductions. Very different particle morphologies were obtained with the catalysts of different F's.

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Influence of support friability and concentration of α‐olefins on gas‐phase ethylene polymerization over polymer‐supported metallocene/methylaluminoxane catalysts

Hammawa

Wanke

2007

J of Applied Polymer Sci

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“…Supported nickel catalysts for olefin polymerization have been described, either using ylide [26,27] or diimine chelate ligands. [28 -31] For both systems, the catalyst was supported before the polymerization.…”

Section: Introductionmentioning

confidence: 99%

Polyethylene Made with In Situ Supported Ni-Diimine/SMAO: Replication Phenomenon and Effect of Polymerization Conditions on Polymer Microstructure and Morphology

Simon

Patel

Soares³

et al. 2001

Macromol. Chem. Phys.

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The catalyst prepared by supporting in situ 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediiminenickel(II) dichloride (1) on silica–methylaluminoxane (SMAO) has high activity for ethylene polymerization, although it is less active than the unsupported system 1/MAO. No external alkylaluminum cocatalyst needs to be added to the in situ supported system. Short chain branches are produced without addition of α‐olefin comonomer, due to the chain‐walking mechanism. Ethylene pressure and polymerization temperature affect the degree of short chain branch formation. At constant ethylene pressure, when the polymerization temperature rises, the short chain branch content also increases. For a given ethylene pressure, there is a threshold polymerization temperature above which polymer particle agglomeration starts to occur. For the conditions investigated herein, from 30 to 50°C the morphology of the polymer particles replicates that of the support. At 55°C, polyethylene starts to become soluble in the reaction medium, and therefore morphological control is gradually lost. Above 70°C, only soluble polymer is produced. Similar results are observed by keeping the temperature constant and changing the ethylene pressure.

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“…The change of selectivity towards polymerization observed with these diketonate nickel complexes after their anchoring on polystyrene resin has been previously observed by us [7,8] after an analogous heterogenization of other nickel complexes active in the homogeneous phase as oligomerization catalysts. This particular behavior can be related to the presence of the bulky polymeric ligand which is responsible for a more tight chelation [23] and, as a consequence, favors the propagation step to give a polymer with respect to ␤-hydrogen elimination, this requiring the liberation of a coordination vacant site from a less hindered intermediate [24] (Scheme 2).…”

Section: ␤-Diketonate Nickel Catalysts / 117mentioning

confidence: 53%

“…In this context, as an extention of our interest in the field of polymer-supported nickel catalysts [7,8], the present work deals with heterogenized nickel catalysts obtained by reaction of Ni(COD) 2 with crosslinked styrene/divinylbenzene (ST/DVB) polymer matrices functionalized with different ␤-diketone moieties (I-IV), and their use for ethylene as well as propylene activation.…”

Section: Introductionmentioning

confidence: 99%

Novel polymer-supported β-diketonate nickel catalysts for α-olefin activation

Benvenuti

Carlini

Galletti

et al. 1998

Polym. Adv. Technol.

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Styrene–divinylbenzene resins were used for the synthesis of different polymer‐bound β‐diketones, obtained by anchoring the chelating group through either the central or the lateral position. The heterogenized diketone ligand was subsequently reacted with Ni(COD)2 analogously to the corresponding homogeneous catalysts active in α‐olefin oligomerization. The heterogenized catalysts showed a good activity only when the central position of the chelate moiety was free. Heterogenization caused a significant change of selectivity: olefin oligomerization was accompanied by the formation of a large amount of polymeric products. This behavior is discussed in terms of steric effects caused by the bulky polymeric ligand. © 1998 John Wiley & Sons, Ltd.

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Supported transition metal complexes for ethylene polymerization

Cited by 25 publications

References 20 publications

Influence of support friability and concentration of α‐olefins on gas‐phase ethylene polymerization over polymer‐supported metallocene/methylaluminoxane catalysts

Influence of support friability and concentration of α‐olefins on gas‐phase ethylene polymerization over polymer‐supported metallocene/methylaluminoxane catalysts

Polyethylene Made with In Situ Supported Ni-Diimine/SMAO: Replication Phenomenon and Effect of Polymerization Conditions on Polymer Microstructure and Morphology

Novel polymer-supported β-diketonate nickel catalysts for α-olefin activation

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