Mechanistic study on comonomer effect in ethylene/1-hexene copolymerization with TiCl4/MgCl2 model Ziegler-Natta catalysts

Jiang, Baiyu; Liu, Xiaoyu; Weng, Yuhong; Fu, Zhisheng; He, Aihua; Fan, Zhiqiang

doi:10.1016/j.jcat.2018.11.034

Cited by 37 publications

(27 citation statements)

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“…Similar phenomena have been found in the previous studies of our group on ethylene and propylene polymerizations with Mt-II/MMAO, where the [C * ]/[M] level was about 70% in the ethylene system and lower than 30% in propylene polymerization (see Table 5 ) [ 30 , 39 , 51 ] It has been explained that the active centers producing polypropylene should be loosely associated ion pairs but not contact ion pairs, since the high steric hindrance in active centers with contact ion pairs will prohibit coordination of the bulky propylene, but allow for ethylene coordination. Therefore, the lower [C*]/[M] level in propylene polymerization can be largely attributed to absence of contact ion pairs in its active center family.…”

Section: Resultssupporting

confidence: 89%

“…Detailed kinetics of zirconium catalyzed ethylene polymerization provides key information for understanding the mechanism of these important industrial processes. As indicated by Busico et al [ 50 , 51 ], the chain propagation constant ( k p ) can be calculated using the “deceptively simple” rate law (Equations (2) and (3)) as follows: R p = k [M] R p = k p [C*][M] where [M] is monomer equilibrium concentration, [E] = 0.085 mol/L in toluene at 50 °C and 0.1 MPa was used for the calculation [ 26 , 52 ]. Since the instant polymerization rate at the time of TPCC quenching ( t p = 20 min) was not determined, the average R p value calculated from the polymer yield after 20 min polymerization and the catalyst amount has been used.…”

Section: Resultsmentioning

confidence: 86%

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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: Resultssupporting

confidence: 89%

Section: Resultsmentioning

confidence: 86%

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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“…[39] In ethylene polymerization with Cat-1/TEA, the [C*]/[Ti] fraction rose from 25 % at 30 s to 60 % after 600 s polymerization, [32] but [C*]/[Ti] of propylene polymerization with this catalyst rose for more than 3 times in 600 s. The increase of [C*]/[Ti] with time has been explained by gradual exposure of shielded Ti species through disintegration of the catalyst particle by hydraulic forces of expanding propagation chains. [32,37,44,45] A possible example of shielded Ti species is shown in Scheme 2a, where the adsorbed TiCl 4 (B) on a MgCl 2 crystallite bridges with a neighboring MgCl 2 crystallite and becomes inaccessible to the cocatalyst. When the growing polymer chains on the nearby active centers expand the gap between the MgCl 2 crystallites, the bridging structure is broken, making the TiCl 4 (B) available to activation.…”

Section: Active Center Models and Mechanistic Discussionmentioning

confidence: 99%

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

et al. 2020

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Kinetics of propylene polymerization with two TiCl 4 /MgCl 2 model catalysts of different Ti load (Cat-1: Ti 0.1 wt%; Cat-2: Ti 1.0 wt%) was investigated in this work. Time-dependent variations of active centers fraction ([C*]/[Ti]) and active center distribution of the two catalysts were compared. In propylene polymerization with Cat-1, [C*]/[Ti] was only 7.8 % in the initial stage, but increased for more than three times in reaction period of 600 s. Propylene polymerization with Cat-2 had much lower [C*]/[Ti]. Active center distributions of the two catalysts were markedly different. Cat-1 has evidently higher proportion of aspecific active centers and less isospecific ones than that of Cat-2. These catalysts also showed different time-dependent variations of active center distribution. The chain propagation rate constant of isospecific centers in Cat-2 was evidently higher than that in Cat-1, but propagation rate constants of either aspecific and medium-isospecific centers were only slightly changed by enhancing Ti content of the catalyst. The results suggest that isospecific centers are mainly originated from clustered Ti species, but non-clustered Ti species are the main source of active centers with lower stereoselectivity. By considering factors like dispersion states of Ti species and release of shielded active species through disintegration of catalyst particles, active center models have been proposed to explain the different kinetic behaviors of the two model catalysts.

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“…Unfortunately, limited by the low loadings as well as the amorphous silica support, the direct characterization of the surface active sites of catalyst including the catalyst H 2 ‐TPR (temperature‐programmed reduction) was failed. As a useful and reliable method, the Flory peak fitting based on the GPC curves has been applied to study properties of the multiple active centers of TiCl 4 /MgCl 2 type Ziegler–Natta [ 35–37 ] and Phillips catalyst. [ 6,31,34 ] The numbers of Schultz–Flory components are used to appraise theoretical site types distribution.…”

Section: Resultsmentioning

confidence: 99%

CrV Bimetallic Phillips Catalyst Prepared by Citric Acid‐Assisted Impregnation on Ethylene Polymerization

Liu

Zhang²,

He³

et al. 2020

Macro Chemistry & Physics

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The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/macp.202000010. Three CrV bimetallic Phillips catalysts are developed by a citric acid-assisted impregnation method and studied in ethylene homopolymerization and ethylene/1-hexene copolymerization. The method benefits to the dispersion of bimetallic active sites, especially for the V ones. The electron binding energy shift of V 2p 3/2 in CrV-1/2-CA suggests the increased electron deficiency of V active center. The CrV-1/2-CA, CrV-1/3-CA catalysts present higher activity, broader molecular weight distribution, than the counterparts without CAassisted impregnation, suggesting more active sites involved in the reaction. The 1-hexene is higher inserted in the polyethylene by CrV-1/2 than the CrV-1/2-CA. But the results of temperature rising elution fractionation-successive selfnucleation and annealing (TREF-SSA) show the thinner platelet thickness at the high molecular weight parts of high-density polyethylene by CrV-1/2-CA, suggesting the higher insertion of 1-hexene and higher tensile properties. The CrV-1/2-CA also shows the more hydrogen-regulated response in the polymerization. The deconvolution of the gel permeation chromatography curves presents the higher fractions of high molecular weight polymer component.

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Mechanistic study on comonomer effect in ethylene/1-hexene copolymerization with TiCl4/MgCl2 model Ziegler-Natta catalysts

Cited by 37 publications

References 59 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

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

CrV Bimetallic Phillips Catalyst Prepared by Citric Acid‐Assisted Impregnation on Ethylene Polymerization

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Mechanistic study on comonomer effect in ethylene/1-hexene copolymerization with TiCl4/MgCl2 model Ziegler-Natta catalysts

Cited by 37 publications

References 59 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

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl2‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

CrV Bimetallic Phillips Catalyst Prepared by Citric Acid‐Assisted Impregnation on Ethylene Polymerization

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Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl₂‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting