Evidences of Long‐<scp>C</scp>hain Branching in Ziegler‐<scp>N</scp>atta Polyethylene Homopolymers as Studied via <scp>SEC</scp>‐<scp>MALS</scp> and Rheology

Yu, Youlu; Rohlfing, David C.

doi:10.1002/masy.201300019

Cited by 6 publications

(12 citation statements)

References 90 publications

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“…Ziegler–Natta HDPE grades are traditionally viewed as the definition of linear polymers. However, recent experimental results clearly indicate the presence of long‐chain branches in certain Z–N HDPE grades . Polymer fractions with a high long‐chain branching content, were detected in the high molecular weight tail of HDPE produced in a slurry‐phase process.…”

Section: Sample Simulation Results and Discussionmentioning

confidence: 97%

“…Finally, it should be noted that the proposed kinetic mechanism includes a terminal double bond reaction resulting in the formation of LCB. Latest developments in polymer characterization (i.e., gel permeation chromatography multi‐angle light scattering (GPC‐MALLS)) and increased accuracy of rheological measurements of industrial polyethylene grades have revealed that under certain conditions (i.e., catalyst, high hydrogen concentration and production of low molecular weight polyethylene), the formation of long chain branches in HDPE is possible …”

Section: Catalytic Olefin Copolymerization Kinetic Mechanism and Specmentioning

confidence: 99%

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A Dynamic Simulator for Slurry‐Phase Catalytic Olefin Copolymerization in a Series of CSTRs: Prediction of Distributed Molecular and Rheological Properties

Pladis

Baltsas

Meimaroglou

et al. 2018

Macro Reaction Engineering

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in low-pressure catalytic (e.g., Ziegler-Natta, metallocenes) solution, slurry and bulk phase reactors. Despite the success of metallocene catalysts the majority of commercial polyolefins are still produced by Ziegler-Natta and Philips chromium catalysts. [1] Continuous slurry-phase polymerization, in the presence of a heterogeneous Ziegler-Natta (Z-N) catalyst, is one of the most commonly employed processes in the production of polyolefins, including high-density polyethylene (HDPE), isotactic polypropylene (IPP) as well as their copolymers with higher olefins. [1][2][3][4][5][6][7][8][9][10] The Z-N slurry-phase olefin polymerization in a series of continuous stirred tank reactors (CSTRs) and loop-reactors continue to dominate the HDPE production, accounting for almost 70% of the total installed capacity. Polymerization in a series of reactors is often employed to control the comonomer incorporation rate and copolymer distribution, which is important for polyolefin grades and applications (e.g., pipes) that require excellent environmental stress crack resistance. The attractive combination of good flowability and improved mechanical properties is achieved by tailoring MWDs and controlling comonomer branching distribution. The slurry-phase HDPE process technology (see Figure 1) employs two or more stirred-tank reactors in series and utilizes a Z-N catalyst system composed of a titanium chloride compound and an alkyl aluminum cocatalyst. The process uses hydrogen as a chain-termination agent to control the molecular weight of the product and a comonomer to control the density of the polyethylene grade. [11] The process operates in a continuous mode using a cascade of two or three autoclave-type vessels. Each reactor can operate under a different hydrogen partial pressure, thereby allowing the control of the molecular weight distribution produced in each reactor of the series. Low molecular-weight polyethylene has a low viscosity and a fast crystallization rate, accounting for high polymer stiffness, whereas high molecular-weight polyolefins exhibit significantly higher toughness, but a much slower crystallization rate and a lower crystallinity together with a high melt viscosity due to extensive polymer chain entanglement. Typical polymerization conditions are: temperatures of 70-90 °C, pressure less than 10 bar and a reactor mean residence time of 45 min.Modeling A comprehensive mathematical model is developed to simulate the dynamic Ziegler-Natta ethylene-α-olefins copolymerization in a series of slurry-phase continuous stirred tank reactors. A generalized multisite kinetic mechanism is considered to describe the molecular and compositional developments (joint molecular weight-copolymer composition distribution) in a series of continuous stirred tank reactors (CSTRs). Dynamic macroscopic mole balances are derived to calculate the dynamic evolution of all species concentrations in three phases (i.e., gas, liquid, and polymer) of the multiphase system. The polymer molecular properties (i.e., molecular weight dist...

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Section: Sample Simulation Results and Discussionmentioning

confidence: 97%

Section: Catalytic Olefin Copolymerization Kinetic Mechanism and Specmentioning

confidence: 99%

A Dynamic Simulator for Slurry‐Phase Catalytic Olefin Copolymerization in a Series of CSTRs: Prediction of Distributed Molecular and Rheological Properties

Pladis

Baltsas

Meimaroglou

et al. 2018

Macro Reaction Engineering

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“…Their M w and η 0 values were determined by GPC and creep test, respectively, where . The relationship between η 0 and M w for linear PE (Figure B) was obtained as log η 0 = −13.99 + 3.58 log M W , which was consistent with that reported in the literature . The creep test curves for sample Control_2 and samples runs 6–8 are shown in Figure A, and the obtained η 0 and M w data are introduced into Figure B.…”

Section: Resultsmentioning

confidence: 99%

In Situ Promotion of Long-Chain Branching in Polyethylene from Ziegler–Natta Catalysts

Liu

Qin

Zhao

et al. 2021

ACS Appl. Polym. Mater.

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Polyethylene (PE) synthesized by Ziegler−Natta catalysts (MgCl 2 /TiCl 4 catalysts) lack long-chain branching (LCB) structure, which to a great extent limits their end uses. In this paper, we report an in situ methodology of incorporating LCB structure into PE of Ziegler−Natta catalysts. The chemistry centers on a bifunctional reagent, ω-alkenylmethyldichlorosilane, where the reagent is first copolymerized with ethylene to anchor on some polymer chains pendant alkylmethyldichlorosilane groups, then upon treating the polymer with water adjacent polymer chainborne alkylmethyldichlorosilane groups undergo one-on-one interchain hydrolytic condensation forming a dimeric alkylmethylsiloxane bridge interconnecting two different polymer chains as H-shape LCB structure. Control of ω-alkenylmethyldichlorosilane concentration during copolymerization is key to realize the chemistry. Gel-free LCB-PEs containing controlled amounts of LCB structure were synthesized by accompanying the copolymerization with hydrogen (H 2 ) as chain transfer agent. The effect of alkenyl chain length of ω-alkenylmethyldichlorosilane on the formation efficiency of LCB structure was studied. The chemistry was generally applicable to different Ziegler−Natta catalysts. LCB-PEs containing increasing amounts of LCB structure exhibited proportionally increased extensional flow properties. Moreover, compared to linear plain PE, LCB-PEs were overall found to increase crystallization rates and thus increase crystallinities.

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“…[14] SEC-FTIR has also been used to quantify the overall branching content as a function of molar mass. [15] The analytical characterization of LCB includes 13 C NMR [16,17] , rheology [18][19][20] and high-temperature SEC with MALLS [21,22] or with triple detection. [23] While NMR and rheology enable to obtain an average content of LCB, SEC-MALLS enables to estimate the distribution of LCB along the molar mass axis.…”

Section: Introductionmentioning

confidence: 99%

“…The analytical characterization of LCB includes 13 C NMR, rheology and high‐temperature SEC with MALLS or with triple detection . While NMR and rheology enable to obtain an average content of LCB, SEC‐MALLS enables to estimate the distribution of LCB along the molar mass axis.…”

Section: Introductionmentioning

confidence: 99%

High‐Temperature Solvent Gradient Liquid Chromatography of Model Long Chain Branched Polyethylenes

Macko

Brüll

Santonja-Blasco

et al. 2015

Macromolecular Symposia

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Summary:The high-temperature solvent gradient liquid chromatography system 1-decanol/1,2,4-trichlorobenzene/porous graphite Hypercarb TM has been applied to the separation of well-defined model long chain branched (LCB) polyethylenes with different architectures (star, H-type, super H-type, pompom, comb). The model LCB polyethylenes have been prepared by anionic polymerization of butadiene followed by click chemistry. After hydrogenation of the polybutadienes, the LCB samples contain $ 2 mol % ethyl branches randomly distributed along the backbone and the LCB, as is typical for linear low density polyethylene (LLDPE). The results indicate that the LCB does not influence the chromatographic separation substantially. The adsorption characteristics of the LCB copolymers are dominated by the SCB content. The presence of LCB increases the molar mass of the samples; however, the increase in molar mass from 100 kg/mol to 200 kg/mol does not influence chromatographic separations in the applied system of porous carbon and 1-decanol/ 1,2,4-trichlorobenzene.

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Evidences of Long‐Chain Branching in Ziegler‐Natta Polyethylene Homopolymers as Studied via SEC‐MALS and Rheology

Cited by 6 publications

References 90 publications

A Dynamic Simulator for Slurry‐Phase Catalytic Olefin Copolymerization in a Series of CSTRs: Prediction of Distributed Molecular and Rheological Properties

A Dynamic Simulator for Slurry‐Phase Catalytic Olefin Copolymerization in a Series of CSTRs: Prediction of Distributed Molecular and Rheological Properties

In Situ Promotion of Long-Chain Branching in Polyethylene from Ziegler–Natta Catalysts

High‐Temperature Solvent Gradient Liquid Chromatography of Model Long Chain Branched Polyethylenes

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