Comments on the Paper “Comparison of the Rheological Properties of Metallocene-Catalyzed and Conventional High-Density Polyethylenes”

Carella, José M.

doi:10.1021/ma960909v

Cited by 20 publications

(16 citation statements)

References 25 publications

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“…The results in Table II display E a values of 25 kJ/mol for both ZNHD‐12 and meHD‐16. This is in accordance with literature numbers28, 52, 53, 55, 56 for linear polyethylenes and seems to confirm that the high elasticity values obtained for ZNHD‐12 were due to the high‐molecular‐weight tail and not to any noticeable amount of longer branches. Also, our experimental homogeneous polymer meHD‐23 displayed a very low E a value, according to our expectations.…”

Section: Resultssupporting

confidence: 92%

“…According to this correlation, an E a of about 34 kJ/mol was obtained for copolymers having a degree of butyl branching of 20 per 1000 carbon atoms. They obtained values of 29–38 kJ/mol for the flow E a 's of metallocene HDPEs, which according to Carella,28 must be an indication of the presence of LCB. A recent article by Vega et al52 suggests that metallocene polymers, with reference to their M w and MWD, show abnormal rheological behavior and some higher flow E a values and may posses low amounts of LCB.…”

Section: Resultsmentioning

confidence: 98%

“…To compare viscosity data with M w and M w / M n data, we used the η*'s taken at 0.02 rad/s [given in Table II as η* (0.02 rad/s)]. As discussed by Carella,28 these values cannot be taken as real values of the zero shear viscosity (η 0 ), but they are still useful for the evaluation of properties. For comparison of the elasticity levels, we applied the method of Han,49 according to which the elasticity can be evaluated by plotting G ′ versus G ″.…”

Section: Resultsmentioning

confidence: 99%

“…Although the homogeneous LLDPEs and HDPEs have better physical properties than heterogeneous LLDPEs and HDPEs, they are even more difficult to process as a result of their narrow MWD. Several articles,2, 3, 24–38 however, have reported that certain classes of metallocene catalysts can produce polymers with controlled amounts of LCB, which leads to both excellent processability and superior mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

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Thermal and rheological studies on the molecular composition and structure of metallocene‐ and Ziegler–Natta‐catalyzed ethylene–α‐olefin copolymers

Starck¹,

Malmberg²,

Löfgren³

2001

J of Applied Polymer Sci

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ABSTRACT:The relationship between the molecular structure and the thermal and rheological behaviors of metallocene-and Ziegler-Natta (ZN)-catalyzed ethylene copolymers and high-density polyethylenes was studied. Of special interest in this work were the differences and similarities of the metallocene-catalyzed (homogeneous) polymers with conventional coordination-catalyzed (heterogeneous) polyethylenes and low-density polyethylenes. The short-chain branching distribution was analyzed with stepwise crystallization by differential scanning calorimetry and by dynamic mechanical analysis. The metallocene copolymers exhibited much more effective comonomer incorporation in the chain than the ZN copolymers; they also exhibited narrower lamellar thickness distributions. Homogeneous, vanadium-catalyzed ZN copolymers displayed a very similar comonomer incorporation to metallocene copolymers at the same density level. The small amplitude rheological measurements revealed the expected trend of increasing viscosity with weight-average molecular weight and shear-thinning tendency with polydispersity for the heterogeneous linear low-density polyethylene and very-low-density polyethylene resins. The high activation energy values (34 -53 kJ/mol) and elevated elasticity found for some of our experimental metallocene polymers suggest the presence of long-chain branching in these polymers. This was also supported by the comparison of the relationship between low shear rate viscosity and molecular weight.

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Section: Resultssupporting

confidence: 92%

Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Thermal and rheological studies on the molecular composition and structure of metallocene‐ and Ziegler–Natta‐catalyzed ethylene–α‐olefin copolymers

Starck¹,

Malmberg²,

Löfgren³

2001

J of Applied Polymer Sci

View full text Add to dashboard Cite

show abstract

“…[ 16,59 ] Vega et al fi rst demonstrated such low levels of LCB in Cp 2 ZrCl 2 -catalyzed PEs in their rheological studies. [ 60,61 ] A patent of Howard et al [ 62 ] from BP Chemicals Ltd. reported the LCB formation of PE in gas-phase polymerization catalyzed by the supported Et[Ind] 2 ZrCl 2 catalyst. Harrison et al [ 63 ] also reported the presence of Scheme 2.…”

Section: Branch Lengthmentioning

confidence: 99%

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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A Comprehensive Review on Controlled Synthesis of Long‐Chain Branched Polyolefins: Part 3, Characterization of Long‐Chain Branched Polymers

Liu

Wang

et al. 2016

Macro Reaction Engineering

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Synthesis and characterization of long-chain branched polyolefins has been an important research topic for both academic and industrial researchers for many decades. This is particularly true since the discovery and successful commercialization of the constrained geometry catalyst systems in 1990s. The type of single site catalysts allows control in the synthesis and the precision in the characterization. Long-chain branched polyolefins exhibit improved melt processability, such as higher melt strength and better shear thinning, compared to their linear counterparts having the same molecular weight and distribution. In the previous papers, the catalyst systems and reaction conditions for the controlled synthesis of long-chain branched polyolefins have been reviewed. This paper aims at summarizing the literatures pertinent to the precise characterization of long-chain branched polyolefins. The major methods of long-chain branching characterization include: nuclear magnetic resonance, gel permeation chromatography, rheometry, dynamical mechanical analysis, differential scanning calorimetry, neutron scattering, and Fourier transform infrared spectroscopy. Recent progresses of these characterization methods, as well as their advantages and limitations, have been discussed in details.

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Comments on the Paper “Comparison of the Rheological Properties of Metallocene-Catalyzed and Conventional High-Density Polyethylenes”

Cited by 20 publications

References 25 publications

Thermal and rheological studies on the molecular composition and structure of metallocene‐ and Ziegler–Natta‐catalyzed ethylene–α‐olefin copolymers

Thermal and rheological studies on the molecular composition and structure of metallocene‐ and Ziegler–Natta‐catalyzed ethylene–α‐olefin copolymers

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

A Comprehensive Review on Controlled Synthesis of Long‐Chain Branched Polyolefins: Part 3, Characterization of Long‐Chain Branched Polymers

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