Effects of alkylaluminum as cocatalyst on the active center distribution of 1-hexene polymerization with MgCl2-supported Ziegler–Natta catalysts

Yang, Hongrui; Zhang, Letian; Zang, Dandan; Fu, Zhisheng; Fan, Zhiqiang

doi:10.1016/j.catcom.2015.01.023

Cited by 22 publications

(9 citation statements)

References 20 publications

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“…In this work, the effects of polymerization time on the catalytic activity and active center ratio in ethylene, propylene polymerizations and ethylene/propylene copolymerization with rac ‐Et(Ind) 2 ZrCl 2 /modified methylaluminoxane (MMAO) were studied and systematically compared. The method of counting the number of active centers adopted in this work is based on selectively quenching the transition metal–polymer bonds with acyl chloride, which has been verified by application in the studies of heterogeneous Ziegler–Natta catalysts . Recently, we have also used the method for kinetic study of metallocene/aluminoxane‐catalyzed ethylene polymerization and obtained reasonable [C * ]/[Mt] values .…”

Section: Introductionmentioning

confidence: 71%

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene, propylene homopolymerizations, and their copolymerization

Guo

Zhang

Guo

et al. 2016

J. Polym. Sci. Part A: Polym. Chem.

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A series of ethylene, propylene homopolymerizations, and ethylene/propylene copolymerization catalyzed with rac‐Et(Ind)2ZrCl2/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2‐thiophenecarbonyl chloride to label a 2‐thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene homopolymerization) and copolymer composition with time were also studied. [C*]/[Zr] strongly depended on type of monomer, with the propylene homopolymerization system presented much lower [C*]/[Zr] (ca. 25%) than the ethylene homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C*]/[Zr] of ethylene homopolymerization (ca. 70%). The chain propagation rate constant (kp) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 867–875

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Section: Introductionmentioning

confidence: 71%

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene, propylene homopolymerizations, and their copolymerization

Guo

Zhang

Guo

et al. 2016

J. Polym. Sci. Part A: Polym. Chem.

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“…27 However, when the E/P ratio was increased further, the number of active centers grew rapidly until 4−5 times higher than that of homopolymerization. 23,32,61 Since the catalyst used in this work has nanopores with an average size of only about 2 nm (Table S11 and Figures S14 and S15), while the lamellar thickness of iPP is far larger than 5 nm, 61 it is difficult for the PP lamellae to grow inside the catalyst's nanopores to expand them for exposing all of the active-center precursors. When ethylene is introduced into the system, the copolymer chains form thinner lamellae (as reflected by their lower melting temperature) that can grow inside smaller nanopores of the catalyst, which cause a larger extent of particle fragmentation.…”

Section: Methodsmentioning

confidence: 99%

“…25−33 Coexistence of more than four types of active centers in the catalyst is widely accepted to explain the broad molecular weight distribution of the produced polyolefin. 26,29,32,33 plicity. 8,27,28,31 In Z−N catalytic copolymerization of different olefins, especially olefin copolymerization of ethylene with other α-olefins, the multisite nature of the catalyst leads to a significantly broad chemical composition distribution (CCD) of the copolymers.…”

Section: Introductionmentioning

confidence: 99%

Responses of a Supported Ziegler–Natta Catalyst to Comonomer Feed Ratios in Ethylene–Propylene Copolymerization: Differentiation of Active Centers with Different Catalytic Features

Zhang

Qian²,

Yang³

et al. 2021

Ind. Eng. Chem. Res.

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Ethylene–propylene (E/P) copolymerization with a TiCl4/Di/MgCl2–TEA/De (Di, internal donor; De, external donor; TEA, triethylaluminum)-type Ziegler–Natta catalyst was conducted at various comonomer feed ratios (E/P ratios). Distribution of active centers among three copolymer fractions (fractions soluble in room-temperature n-octane (C8-sol) and boiling n-heptane (C7-sol) and fraction insoluble in boiling n-heptane (C7-insol)) and their change with the E/P ratio were studied by quench-labeling the copolymerization, fractionating the copolymer, and measuring the labeled group in each fraction. By comparing with the active-center distribution of propylene homopolymerization, active centers in copolymerization were differentiated into three categories having low, medium, and high stereoselectivities. At E/P ≥ 40/60, the category of isospecific active centers produced the majority of the C8-sol fraction composed of the random copolymer (rEP). The majority of the active centers with medium isoselectivity also produced rEP, while a small fraction produced segmented copolymers (sEP) containing crystalline polyethylene (PE) segments. The active-center category of low stereoselectivity produced copolymers with very long PE segments in C7-insol. There is evidence that a small proportion of high isospecific centers produced sEP chains containing long crystallizable polypropylene (PP) segments, which can work as compatibilizers in high-impact polypropylene (PP/EP reactor alloy). Using a De type enabling production of PP with higher isotacticity in homopolymerization, more sEP chains having longer crystallizable PP segments were formed in copolymerization.

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“…Any modification of each component will have an effect on their ACD [2,3]. ID can bind strongly to MgCl 2 crystallites formed in the preparation process, thus stabilizing these crystallites.…”

Section: Introductionmentioning

confidence: 99%

Effects of alkylaluminum as cocatalyst on the active center distribution of 1-hexene polymerization with MgCl2-supported Ziegler–Natta catalysts

Cited by 22 publications

References 20 publications

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene, propylene homopolymerizations, and their copolymerization

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene, propylene homopolymerizations, and their copolymerization

Responses of a Supported Ziegler–Natta Catalyst to Comonomer Feed Ratios in Ethylene–Propylene Copolymerization: Differentiation of Active Centers with Different Catalytic Features

Effect of internal electron donor on the active center distribution in MgCl2-supported Ziegler–Natta catalyst

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