Revisiting the long-chain branch formation mechanism in metallocene catalyzed polyethylenes

Karimkhani, Vahid; Afshar‐Taromi, Faramarz; Pourmahdian, Saeed; Stadler, Florian J.

doi:10.1039/c3py00319a

Cited by 30 publications

(27 citation statements)

References 80 publications

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“…Moreover, polymer chains containing a terminal vinyl group, created in situ, can be also incorporated into the growing chains, leading to the formation of long-chain branched (LCB) polymers. With higher affinity to comonomer incorporation comes better chances of LCB formation [10,11]. Narrow molecular weight distribution made by metallocenes leads to enhanced mechanical properties, but decreases melt processability.…”

Section: Introductionmentioning

confidence: 99%

Complex interplay of short- and long-chain branching on thermal and rheological properties of ethylene/α-olefin copolymers made by metallocene catalysts with oscillating ligand structure

Ahmadi

Rezaei

Mortazavi

et al. 2017

Polymer

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Unbridged oscillatory metallocenes are prone to produce heterogeneous chain microstructure, for instance, giving rise to elastomeric polypropylene. Here, we use the bis(2phenylindenyl)ZrCl 2 /MAO catalyst system, featuring oscillating ligands, to copolymerize ethylene with several α-olefins. Through investigation of chain microstructure, thermal and rheological properties, we show that the complex behavior of these materials can be justified by considering a catalyst with dual active center having different comonomer affinities. This behavior is consistent with the proposed mechanism of fast oscillating ligands, becoming locked upon proximity of cocatalyst counteranion, leading to diverse stereo-and comonomer selectivity. The unlocked, oscillating active center with lower comonomer response gives rise to mostly linear chains and is not affected by the presence of comonomer, while the locked one creates long chain branched chains, whose frequency decreases by introduction of comonomer. Copolymer samples exhibited bimodal MWD, dual crystallization mechanisms, and low frequency plateau modulus, specifically at higher comonomer levels. It was concluded that the overall behavior is determined by complex interplay of SCB and LCB, which leads to thermorheological complexity as well as phase separation.Oscillating metallocene catalyst is used in copolymerization of ethylene and several α-olefin comonomers. The dual nature of active centers leading to complex interplay of SCB and LCB is revealed by studying thermal and rheological properties. Graphical Abstract Complex interplay of short and long-chain branching on thermal and rheological properties of ethylene/α-olefin copolymers made by oscillatory metallocene catalystMostafa Ahmadi, Faeze Rezaei, Mohammad Mehdi Mortazavi, Mehdi Entezam, Florian J. StadlerOscillating metallocene catalyst is used in copolymerization of ethylene and several α-olefin comonomers. The dual nature of active centers leading to complex interplay of SCB and LCB is revealed by studying thermal and rheological properties.

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Section: Introductionmentioning

confidence: 99%

Complex interplay of short- and long-chain branching on thermal and rheological properties of ethylene/α-olefin copolymers made by metallocene catalysts with oscillating ligand structure

Ahmadi

Rezaei

Mortazavi

et al. 2017

Polymer

Self Cite

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“…reported the rheological properties of several sets of linear and long-chain branched homo-and copolymers made using the catalysts described by Stevens and Neithamer (1992). This type of half-metallocene catalyst is similar to those described by Canich (1991), although other metallocene catalysts, such as those used by Piel et al (2006), could in principle be used to produce similar branched structures, as shown by Karimkhani et al (2013). A subsequent report [Costeux et al (2002)] described a solution polymerization model for polyethylenes made using this type of catalyst in a continuous stirred tank reactor (CSTR), which was able to predict the distributions of chain segment types present.…”

Section: Introductionmentioning

confidence: 65%

“…Malmberg et al (2002) observed strain hardening in long-chain BMPs, but their samples were made in a semibatch slurry process. The important differences between materials made in a slurry process and those made in solution have been discussed by Karimkhani et al (2013). Some of the polymers dealt with in that study (those made with catalyst D, except D5) may be similar to the ones we studied.…”

Section: Molecular Modeling Of Rheological Behaviormentioning

confidence: 79%

Branching structure and strain hardening of branched metallocene polyethylenes

Torres¹,

Li²,

Costeux³

et al. 2015

Journal of Rheology

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Published by the The Society of Rheology Articles you may be interested inStrain hardening of molten thermoplastic polymers reinforced with poly(tetrafluoroethylene) nanofibers J. Rheol. 58, 589 (2014); 10.1122/1.4867389 Extensional rheology of shear-thickening fumed silica nanoparticles dispersed in an aqueous polyethylene oxide solution J. Rheol. 58, 411 (2014); 10.1122/1.4864620 Solution and melt viscoelastic properties of controlled microstructure poly(lactide) AbstractThere have been a number of studies of a series of branched metallocene polyethylenes (BMPs) made in a solution, continuous stirred tank reactor (CSTR) polymerization. The materials studied vary in branching level in a systematic way, and the most highly branched members of the series exhibit mild strain hardening. An outstanding question is which types of branched molecules are responsible for strain hardening in extension. This question is explored here by use of polymerization and rheological models along with new data on the extensional flow behavior of the most highly branched members of the set. After reviewing all that is known about the effects of various branching structures in homogeneous polymers and comparing this with the structures predicted to be present in BMPs, it is concluded that in spite of their very low concentration, treelike molecules with branch-on-branch structure provide a large number of deeply buried inner segments that are essential for strain hardening in these polymers. V C 2015 The Society of Rheology.

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“…Their conclusion is based on the experimental observation about the effects of various polymerization parameters including pressure, temperature and comonomer type and concentration on the LCBD of resulted polymers. [ 71 ] Nevertheless, the exact LCB Figure 2. Meso and rac-diastereomers of 1-and 2-tert -butyldimethylsiloxy-substituted ethylenebis(indenyl)zirconium dichlorides (meso-1, rac-1, meso-2, rac-2).…”

Section: Branch Lengthmentioning

confidence: 95%

A Comprehensive Review on Controlled Synthesis of Long-Chain Branched Polyolefins: Part 1, Single Catalyst Systems

Liu

Wang

et al. 2016

Macromol. React. Eng.

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Polyolefins (POs) are the largest polymer product in the world. The innovation in converting commodity olefin monomers to highly value added high‐performance POs has been and will continue to be a major theme in both academic research and industry practice. The excellent properties of POs can be achieved through precise engineering of their chain architectures, which largely involves control of the chain branching structures. Long‐chain branching is one of the most important parameters in the aspect of various chain branching structures. A huge amount of literatures have been reported to achieve better control of long‐chain branched structures over the last two decades. Recently, good effort has been made in reviewing all the major literatures and summarizing the catalytic systems and synthetic strategies for the controlled synthesis of long‐chain branched POs. This paper represents the first of the series, that is, controlled synthesis of long‐chain branched POs via single catalyst systems.

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Revisiting the long-chain branch formation mechanism in metallocene catalyzed polyethylenes

Cited by 30 publications

References 80 publications

Complex interplay of short- and long-chain branching on thermal and rheological properties of ethylene/α-olefin copolymers made by metallocene catalysts with oscillating ligand structure

Complex interplay of short- and long-chain branching on thermal and rheological properties of ethylene/α-olefin copolymers made by metallocene catalysts with oscillating ligand structure

Branching structure and strain hardening of branched metallocene polyethylenes

A Comprehensive Review on Controlled Synthesis of Long-Chain Branched Polyolefins: Part 1, Single Catalyst Systems

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