External silane donors in Ziegler—Natta catalysis: a two-site model simulation of the effects of various alkoxysilane compounds

Härkönen, Mika; Seppälä, Jukka; Chûjô, Riichirǒ; Kogure, Yoshiaki

doi:10.1016/0032-3861(95)95929-u

Cited by 37 publications

(20 citation statements)

References 13 publications

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“…The concept that an alkoxysilane donor, as well as poisoning weakly specific sites, can reversibly transform such sites into isospecific species, has also been proposed by other groups. [31 -33] It was suggested [33] that the high stereospecificity obtained using silanes having one or more bulky hydrocarbyl groups was due to the silane stabilizing "fluctuating" isospecific sites, the bulky hydrocarbyl groups protecting the silane from removal from the catalyst surface via complexation with aluminium alkyl. We have observed that the use of Al(i-Bu) 3 rather than AlEt 3 as cocatalyst in propene polymerization using the catalyst system MgCl 2 /TiCl 4 /DIBP-AlR 3 -alkoxysilane can give a broadening in molecular weight distribution, as a result of the presence of a fraction having high isotactic stereoregularity and high molecular weight.…”

Section: Resultsmentioning

confidence: 99%

Effects of Internal and External Donors on the Regio- and Stereoselectivity of Active Species in MgCl2-Supported Catalysts for Propene Polymerization

Chadwick¹,

Morini²,

Balbontin³

et al. 2001

Macromol. Chem. Phys.

129

111

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Section: Resultsmentioning

confidence: 99%

Effects of Internal and External Donors on the Regio- and Stereoselectivity of Active Species in MgCl2-Supported Catalysts for Propene Polymerization

Chadwick¹,

Morini²,

Balbontin³

et al. 2001

Macromol. Chem. Phys.

129

111

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“…A possible reason for the advantages of the silanes with bulky alkyl substituents is their weaker ability to form complexes with organoaluminum cocatalysts, which prevents removal of the silanes from the catalyst surface. [32] No obvious correlation between the common fractionation data for the poly(propylene) samples (such as the content of the highly crystalline fraction in the polymers, in Table 1) and the average isotacticity of the dominant components in the same fractions (Table 4) could be traced.…”

Section: Experimental Partmentioning

confidence: 99%

Isoselectivity Distribution of Isospecific Centers in Supported Titanium‐Based Ziegler‐Natta Catalysts

Kissin

Chadwick

Mingozzi

et al. 2006

Macro Chemistry & Physics

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Summary: This article describes the quantitative aspects of the isoselectivity distribution of isospecific centers in five supported titanium‐based Ziegler–Natta catalyst systems containing different internal and external organic donors. Highly crystalline poly(propylene) fractions of the polymers (insoluble in o‐xylene at 95 °C) were analyzed by analytical Tref and gel permeation chromatography (GPC) methods. Separation of the Tref curves into the peaks of sterically uniform components (each represented by the Lorentz function) showed that all these “isotactic” poly(propylene) fractions are nonuniform materials. Each highly crystalline fraction contains several distinct components that differ in stereoregularity. The [mmmm] values for different components (which have approximately the same isotacticity in different polymers) range from as high as 0.986–0.993 to much lower values, in the 0.935–0.955 range. The number of Tref components and their relative contents are substantially different for the crystalline fractions of the polymers produced with different catalyst systems; these parameters depend on the nature of the internal and the external electron donors in the catalysts. GPC analysis of the crystalline poly(propylene) fractions showed that each consists of four or five Flory components (the components produced by kinetically uniform active centers) with widely different average molecular weights, from ≈1 × 104 to ≈1.3 × 106. In general, the probabilities of chain transfer reactions for different active centers decrease with the increase in their isospecificity.Resolution of the Tref curve of the highly crystalline fraction of poly(propylene) prepared with catalyst system 3.magnified imageResolution of the Tref curve of the highly crystalline fraction of poly(propylene) prepared with catalyst system 3.

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“…[14][15][16] Even though many scientists explained isospecificity increase by the existence of donors according to these results, the effects of donors are considered to be more complicated. [17][18][19] For the further improvement of the Ziegler-Natta catalyst system, it is essential to understand how donors interact with other components of the catalyst. The internal donor coordinated to the MgCl 2 surface is desorbed from the solid catalyst by the reaction with alkylaluminum.…”

Section: Introductionmentioning

confidence: 99%

External Donor Induced Direct Contact Effects on Mg(OC₂H₅)₂‐Based Ziegler‐Natta Catalysts for Propylene Polymerization

Kim

Hiraoka

Taniike

et al. 2009

Macromolecular Symposia

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Summary: Effects of external donor induced direct contact without alkylaluminum were studied for Ziegler-Natta catalysts containing monoester and diester as internal donors on the catalytic performances such as activity and stereoselectivity. Traditional slurry polymerizations were carried out for rather short period after direct contact for a variety of time. GC analysis was also performed to observe replacement phenomena of donors during direct contact. It was postulated that the different performances of the catalysts were greatly affected by the pair of internal and external donors.

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External silane donors in Ziegler—Natta catalysis: a two-site model simulation of the effects of various alkoxysilane compounds

Cited by 37 publications

References 13 publications

Effects of Internal and External Donors on the Regio- and Stereoselectivity of Active Species in MgCl2-Supported Catalysts for Propene Polymerization

Effects of Internal and External Donors on the Regio- and Stereoselectivity of Active Species in MgCl2-Supported Catalysts for Propene Polymerization

Isoselectivity Distribution of Isospecific Centers in Supported Titanium‐Based Ziegler‐Natta Catalysts

External Donor Induced Direct Contact Effects on Mg(OC₂H₅)₂‐Based Ziegler‐Natta Catalysts for Propylene Polymerization

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External silane donors in Ziegler—Natta catalysis: a two-site model simulation of the effects of various alkoxysilane compounds

Cited by 37 publications

References 13 publications

Effects of Internal and External Donors on the Regio- and Stereoselectivity of Active Species in MgCl2-Supported Catalysts for Propene Polymerization

Effects of Internal and External Donors on the Regio- and Stereoselectivity of Active Species in MgCl2-Supported Catalysts for Propene Polymerization

Isoselectivity Distribution of Isospecific Centers in Supported Titanium‐Based Ziegler‐Natta Catalysts

External Donor Induced Direct Contact Effects on Mg(OC2H5)2‐Based Ziegler‐Natta Catalysts for Propylene Polymerization

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External Donor Induced Direct Contact Effects on Mg(OC₂H₅)₂‐Based Ziegler‐Natta Catalysts for Propylene Polymerization