Influence of long-chain branches in polyethylenes on linear viscoelastic flow properties in shear

Gabriel, Claus; Münstedt, Helmut

doi:10.1007/s00397-001-0219-6

Cited by 152 publications

(165 citation statements)

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“…The fact that only about 3% of the deformation induced by a creep deformation for t 0 = 4150 s recoverable (Figure 3), illustrates that this anomalous behavior is not the consequence of a network, as in that case the viscous part of the deformation (about 97%) would be much smaller in comparison to the elastic part (ideally 0%) [53]. In single-phase melts besides cross-linking, only a high molecular component is known to be able to elevate J e to a level above 10 -2 Pa -1 [46,54]. However, the presence of such a high molecular component in F18G can be excluded, as such a high molecular component would certainly be detected by SEC-MALLS, which reacts very sensitively towards high molecular components even in very small concentrations.…”

Section: Elastic Behaviormentioning

confidence: 87%

Evidence of intra-chain phase separation in molten short-chain branched polyethylene

Stadler¹

2011

Express Polym. Lett.

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Abstract. Intramolecular phase separation is usually associated with block-copolymers, but the same phenomenon is also obtainable by random-copolymers. In this article, evidence of intramolecular phase separation is reported for a linear octadecene-ethene copolymer, which shows an evolving 'yield point' at a long time and low frequency. This is attributed to a partial phase separation of the long short-chain branches. In creep recovery, this behavior is evident as increasing elastic steady-state creep recovery compliance J e 0 . In contrast to 'normal' block-copolymers, this special polymer has an increase in phase separation with temperature, which is caused by the chemical composition and the short chain segments in the side chain domain, leading to a high surface fraction. Vol.5, No.4 (2011) 327-341 Available online at www.expresspolymlett.com DOI: 10.3144/expresspolymlett.2011 * Corresponding author, e-mail: fjstadler@jbnu.ac.kr © BME-PT length in their paper, as it cannot be determined due to the synthesis method. Such block-copolymers are usually thermorheologically complex [9,14,15]. The group of Bates [9,10], for example, found that below the order-disorder transition temperature, i.e., in the ordered state, the sample behaves like a gel and thermorheologically simple, while in the disordered state, a clear thermorheological complexity is found. The higher the temperature, the less pronounced the long-term relaxation process and, thus, the more similar is the data to a single-phase polymer melt. Recently, it was also proven that pure ethylene-/!-olefin copolymers with very long comonomers (C26) can be phase separating in the solid state, if their comonomer content is sufficiently high [16]. This effect is different from the previous cases, because it only involves one type of chain and, furthermore, occurs on random copolymers. Hence, it is an effect that occurs only on a short length scale, as shown by the fact that the length of the comonomers used were 18 and 26 carbons. Thus, the second phase has to encompass only the maximum of 24 terminal carbons; realistically, 16-20 carbons. This effect had a small trace in X-ray diffraction, which points to a weak side chain crystallization [17,18]. However, it was shown that the samples showing this phase behavior in the solid state [16] did not show it in the melt state, as the samples behaved like normal linear low density polyethylenes (LLDPEs), being only special because of their higher flow activation energy E a , which is the consequence of the side-chain content s c of the comonomer [19,20]. Phase separation in the melt is usually visible by traces of the interfacial tension [21] and different temperature dependencies of the individual blend components and the interfacial processes [22,23]. Hence, if other techniques don't show any trace, e.g., because of too low differences in the electron density in X-ray scattering, rheological behavior can provide a valuable aid to the characterization of phase separation. Recently, molecular dynamics studies revea...

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Section: Elastic Behaviormentioning

confidence: 87%

Evidence of intra-chain phase separation in molten short-chain branched polyethylene

Stadler¹

2011

Express Polym. Lett.

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“…In similar vein, the steady-state recoverable elastic compliance, J 0 e is also correlated with LCB; unfortunately, it is also correlated in the same manner with molecular weight distribution which makes it hard to tease the apart the two effects [287][288][289][290]. In addition, the measurement of J 0 e is more time-consuming than that of η 0 , and in many practical cases steady state may not even be experimentally attainable [277,291].…”

Section: Experimental Methodsmentioning

confidence: 99%

Analytical Rheology of Polymer Melts: State of the Art

Shanbhag

2012

ISRN Materials Science

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The extreme sensitivity of rheology to the microstructure of polymer melts has prompted the development of "analytical rheology," which seeks inferring the structure and composition of an unknown sample based on rheological measurements. Typically, this involves the inversion of a model, which may be mathematical, computational, or completely empirical. Despite the imperfect state of existing models, analytical rheology remains a practically useful enterprise. I review its successes and failures in inferring the molecular weight distribution of linear polymers and the branching content in branched polymers.

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“…[1][2][3][4][5][6][7][8][9] Thus far, however, most research efforts aiming to explore the fundamental role of branches in polymer science have mainly focused on long-chain branched polymers, 2,[10][11][12][13][14][15][16] although it is equally well known that short-chain branching generally significantly affects a wide variety of physical properties such as crystallinity, melting point, modulus, and the hardness of polymeric materials. [16][17][18] From a thermodynamic viewpoint, 19 the standard approach would be to analyze the structure of polymers in solution or melt by accounting simultaneously for the energetics (polymer-polymer and polymer-solvent) and (intramolecular and intermolecular) entropy of the system, and then to determine the properties of the system based on the resulting structural information. This conventional approach, though generally effective for long-chain branched polymers, may cause significant errors in the case of polymeric materials containing chains with branches along the main backbone that are rather short, as this is likely to lead to the presumption of a negligible entropic contribution by such short branches.…”

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confidence: 99%

Communication: Role of short chain branching in polymer structure and dynamics

Kim

Baig

2016

The Journal of Chemical Physics

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A comprehensive understanding of chain-branching effects, essential for establishing general knowledge of the structure-property-phenomenon relationship in polymer science, has not yet been found, due to a critical lack of knowledge on the role of short-chain branches, the effects of which have mostly been neglected in favor of the standard entropic-based concepts of long polymers. Here, we show a significant effect of short-chain branching on the structural and dynamical properties of polymeric materials, and reveal the molecular origins behind the fundamental role of short branches, via atomistic nonequilibrium molecular dynamics and mesoscopic Brownian dynamics by systematically varying the strength of the mobility of short branches. We demonstrate that the fast random Brownian kinetics inherent to short branches plays a key role in governing the overall structure and dynamics of polymers, leading to a compact molecular structure and, under external fields, to a lesser degree of structural deformation of polymer, to a reduced shear-thinning behavior, and to a smaller elastic stress, compared with their linear analogues. Their fast dynamical nature being unaffected by practical flow fields owing to their very short characteristic time scale, short branches would substantially influence (i.e., facilitate) the overall relaxation behavior of polymeric materials under various flowing conditions.

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Influence of long-chain branches in polyethylenes on linear viscoelastic flow properties in shear

Cited by 152 publications

References 34 publications

Evidence of intra-chain phase separation in molten short-chain branched polyethylene

Evidence of intra-chain phase separation in molten short-chain branched polyethylene

Analytical Rheology of Polymer Melts: State of the Art

Communication: Role of short chain branching in polymer structure and dynamics

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