Determination and tracing of active and dormant propagation chains in 1-hexene polymerization with supported Ziegler-Natta catalyst

Yang, Pengjia; Zhong, Wentao; Jiang, Baiyu; Zhang, Biao; Fu, Zhisheng; Fan, Zhiqiang

doi:10.1016/j.apcata.2020.117469

Cited by 13 publications

(11 citation statements)

References 42 publications

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“…It will be interesting to know how to clarify the mechanism of the observed effects, the changes of active center concentration as well as the apparent chain propagation constant with the alkylaluminum type and concentration. It will also be interesting to know how to determine the following effect by the quench-labeling method using 2-thiophenecarbonyl chloride (TPCC) as the quencher based on selectively quenching the metal-polymer bonds through acyl chloride, which has been verified in our previous study by application in the polymerization of olefins with Ziegler–Natta, nickel–diimine and metallocene catalysts [ 39 , 41 , 42 , 43 , 44 ]. Thus, it would be worthwhile to understand the mechanism of cocatalyst effects on PE molecular weight, MWD mono-modal to bimodal type and unsaturated chain ends formed via β-H transfer, which have investigated by 1 H NMR and GPC (Flory components) analysis.…”

Section: Introductionmentioning

confidence: 99%

Kinetic and Thermal Study of Ethylene and Propylene Homo Polymerization Catalyzed by ansa-Zirconocene Activated with Alkylaluminum/Borate: Effects of Alkylaluminum on Polymerization Kinetics and Polymer Structure

et al. 2021

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The kinetics of ethylene and propylene polymerization catalyzed by homogeneous metallocene were investigated using 2-thiophenecarbonyl chloride followed by quenched-flow methods. The studied metallocene catalysts are: rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (Mt-I), rac-Et(Ind)2ZrCl2 (Mt-II) activated with ([Me2NPh][B(C6F5)4] (Borate-I), [Ph3C][B(C6F5)4] (Borate-II), and were co-catalyzed with different molar ratios of alkylaluminum such as triethylaluminium (TEA) and triisobutylaluminium (TIBA). The change in molecular weight, molecular weight distribution, microstructure and thermal properties of the synthesized polymer are discussed in detail. Interestingly, both Mt-I and Mt-II showed high activity in polyethylene with productivities between 3.17 × 106 g/molMt·h to 5.06 × 106 g/molMt·h, activities were very close to each other with 100% TIBA, but Mt-II/borate-II became more active when TEA was more than 50% in cocatalyst. Similarly, Polypropylene showed the highest activity of 11.07 106 g /molMt·h with Mt-I/Borate-I/TIBA. The effects of alkylaluminum on PE molecular weight were much more complicated; MWD curve changed from mono-modal in Mt-I/borate-I/TIBA to bimodal type when TIBA was replaced by different amounts of TEA. In PE, the active center fractions [C*]/[Zr] of Mt-I/borate were higher than that of Mt-II/borate and average chain propagation rate constant (kp) value slightly decreased with the increase of TEA/TIBA ratio, but the Mt-II/borate systems showed higher kp 1007 kp (L/mol·s). In PP, the Mt-I/borate presented much higher [C*]/[Zr] and kp value than the Mt-II. This work also extend to investigate the mechanistic features of zirconocenes catalyzed olefin polymerizations that addressed the largely unknown issues in zirconocenes in the distribution of the catalyst, between species involved in polymer chain growth and dormant state. In both metallocene systems, chain transfer with alkylaluminum is the dominant way of chain termination. To understand the mechanism of cocatalyst effects on PE Mw and (MWD), the unsaturated chain ends formed via β-H transfer have been investigated by 1H NMR analysis.

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Section: Introductionmentioning

confidence: 99%

Kinetic and Thermal Study of Ethylene and Propylene Homo Polymerization Catalyzed by ansa-Zirconocene Activated with Alkylaluminum/Borate: Effects of Alkylaluminum on Polymerization Kinetics and Polymer Structure

et al. 2021

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“…However, for lack of efficient methods of counting active centers in Z−N catalysts, there are very few studies that report the number of active centers (molar ratio of [C*]/ [M T ], where C* denotes the active center and M T denotes the transition metal in the catalyst) in olefin copolymerization with Z−N catalysts. 48,51 In our previous works, an efficient and reliable method of counting the active centers in olefin polymerization with Z−N catalysts based on the quenchlabeling technique was developed, 24,31,53 which has been applied in mechanistic studies on ethylene−α-olefin copolymerization with supported Z−N catalysts. 23,39,54,55 These research works have produced unprecedented experimental results that enable deeper insights into the catalytic mechanism and catalyst structure.…”

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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“…The quench-labeling reactions can be depicted in the following equations (see Scheme 1), wherein thiophene-2-carbonyl chloride (TPCC) was used as the quenching agent and propylene was the monomer: Since chain transfer of propagation chains with an alkylaluminum cocatalyst takes place in most catalytic olefin polymerization, the possible reaction of Al−polymeryl (the chain transfer product) with acyl chloride must be considered in acyl chloride quenchlabeling reactions (see Scheme 2). In our previous works, this side reaction was found to be completely depressed when the acyl chloride/alkylaluminum molar ratio was larger than 1 [21,22,24]. This effect could be explained by the deactivation of Al−polymeryl by excess acyl chloride.…”

Section: Methodsmentioning

confidence: 87%

“…The necessity of using excess acyl chloride quencher results in a heavy burden on polymer purification after the quenching reaction as well as waste of expensive quencher because in most catalytic olefin polymerizations, the molar ratio of alkylaluminum to transition metal is larger than 50. In our previous works, the molar ratio of acyl chloride quencher over transition metal in the catalyst was usually larger than 100 [19][20][21][22]24,[27][28][29]. To reduce the amount of acyl chloride quencher in the quench-labeling system, a possible solution could be to replace a part of the quencher with an organic electron donor that did not react with the alkylaluminum cocatalyst.…”

Section: Methodsmentioning

confidence: 99%

Modification of the Acyl Chloride Quench-Labeling Method for Counting Active Sites in Catalytic Olefin Polymerization

Yang

Zhang²,

Zhong

et al. 2021

Catalysts

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The reliable and efficient counting of active sites in catalytic olefin polymerization has been realized by using acyl chloride as the quench-labeling agent. However, the molar ratio of acyl chloride to the alkylaluminum cocatalyst must be larger than 1 in order to completely depress side reactions between the quencher and Al-polymeryl that is formed via chain transfer reaction. In this work, a tetrahydrofuran/thiophene-2-carbonyl chloride (THF/TPCC) mixture was used as the quenching agent when counting the active sites of propylene polymerization catalyzed by MgCl2/Di/TiCl4 (Di = internal electron donor)-type Ziegler–Natta catalyst activated with triethylaluminum (TEA). When the THF/TEA molar ratio was 1 and the TPCC/TEA molar ratio was smaller than 1, the [S]/[Ti] ratio of the polymer quenched with the THF/TPCC mixture was the same as that quenched with only TPCC at TPCC/TEA > 1, indicating quench-labeling of all active sites bearing a propagation chain. The replacement of a part of the TPCC with THF did not influence the precision of active site counting by the acyl chloride quench-labeling method, but it effectively reduced the amount of acyl chloride. This modification to the acyl chloride quench-labeling method significantly reduced the amount of precious acyl chloride quencher and brought the benefit of simplifying polymer purification procedures after the quenching step.

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Determination and tracing of active and dormant propagation chains in 1-hexene polymerization with supported Ziegler-Natta catalyst

Cited by 13 publications

References 42 publications

Kinetic and Thermal Study of Ethylene and Propylene Homo Polymerization Catalyzed by ansa-Zirconocene Activated with Alkylaluminum/Borate: Effects of Alkylaluminum on Polymerization Kinetics and Polymer Structure

Kinetic and Thermal Study of Ethylene and Propylene Homo Polymerization Catalyzed by ansa-Zirconocene Activated with Alkylaluminum/Borate: Effects of Alkylaluminum on Polymerization Kinetics and Polymer Structure

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

Modification of the Acyl Chloride Quench-Labeling Method for Counting Active Sites in Catalytic Olefin Polymerization

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