From dynamic moduli to molecular weight distribution: A study of various polydisperse linear polymers

Carrot, Christian; Guillet, Jacques

doi:10.1122/1.550815

Cited by 81 publications

(48 citation statements)

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“…Frequency sweep experiments provide the elastic (G 0 ) and loss (G 00 ) moduli, the base input for the molar mass evaluation. As stated by Carrot and Guillet, 43 the accuracy of the weight-average molecular weight prediction is mainly determined by the low frequency limit of the measurements, which in this case is 10 -3 rad/s. Figure 5 shows series of frequency sweep experiments performed on samples with different molar masses.…”

Section: Resultsmentioning

confidence: 99%

Molar Mass and Molecular Weight Distribution Determination Of UHMWPE Synthesized Using a Living Homogeneous Catalyst

Talebi¹,

Duchateau²,

et al. 2010

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Understanding of the physical characteristics of a polymer requires molar mass determination. For the commercially available polymers, having average molar mass below 1 000 000 g/mol, chromatography is the method that is often applied to determine the molar mass and molar mass distribution. However, the application of conventional chromatography techniques for polymers having molar mass >1 000 000 g/mol becomes very challenging, and often the results are disputed. In this article, melt rheometry based on the "modulus model" is utilized to measure the molar mass and polydispersity of ultra highmolecular-weight polyethylenes (UHMWPEs) having molar mass >1 000 000 g/mol. Results are compared with the chromatography data of the same polymer samples and the boundary conditions where the chromatography technique fails, whereas the rheometry provides the desired information is discussed. The rheological method is based on converting the relaxation spectrum from the time domain to the molecular weight domain and then using a regularized integral inversion to recover the molecular weight distribution curve. The method is of relevance in determining very high molar masses (exceeding 3 000 000 g/mol) that cannot be ascertained conclusively with the existing chromatography techniques. For this study, UHMWPEs with various weight-average molar masses, where the number-average molar mass exceeds >1 000 000 g/mol, are synthesized. Catalyst used for the synthesis is a living homogeneous catalyst system: MAO-activated bis(phenoxy imine) titanium dichloride. The rheological behavior of the thus synthesized nascent reactor powders confirms the disentangled state of the polymer that tends to entangle with time in melt.

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Section: Resultsmentioning

confidence: 99%

Molar Mass and Molecular Weight Distribution Determination Of UHMWPE Synthesized Using a Living Homogeneous Catalyst

Talebi¹,

Duchateau²,

et al. 2010

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“…For more complex multimodal w(M), this form can be extended to include a sum of generalized exponential models [231,261,262]. [263].…”

Section: (I) Regularization Extraction Of H(τ) In (10) and W(m) In (mentioning

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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“…A value of G N o of 1.0·10 6 Pa has been used for mPEs [150]. For chromiumbased PEs, a value of 1.5·10 6 Pa, commonly used in this type of calculation for HDPE and LLDPE, was previously selected [185]. The value of G N o for PE has generated much controversy, and values ranging from 1.1·10…”

Section: Predicting the Presence Of Lcb From Mwdmentioning

confidence: 99%

“…1 together with the values of G N o obtained from rheological measurements and the literature [150,177,185]. A value of G N o of 1.0·10 6 Pa has been used for mPEs [150].…”

Section: Predicting the Presence Of Lcb From Mwdmentioning

confidence: 99%

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

et al. 2002

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Abstract:The aim of this review is to provide evidence that rheological testing is a potent tool for characterising polymers in the melt. An effort has been made in order to gather results in conventional and model polyolefins, and correlating them with phenomena occurring at the molecular level. We have focused our interest on long chain branching (LCB). In the case of materials containing long side-chain branches, strong effects on viscosity, elastic character and activation energy of flow are general features. Literature results mostly indicate that the effect of polydispersity on these parameters could be very similar to that expected due to the presence of LCB -notwithstanding that the effects of LCB seem to be stronger than those due to polydispersity for a given molecular weight. Different relaxation processes appear as a consequence of the presence of LCB: slower terminal relaxation behaviour than of linear counterparts, and faster additional branch relaxation at higher frequencies, clearly distinguishable from polydispersity effects. To measure the amount of LCB from limited viscoelastic data and molecular properties seems to be a suitable instrument to explain the rheological features of the different polymers, but it fails when the results are compared with measured values of LCB density in model polymers. The actual framework leads us to say that the number of branches is less important than the topology itself. Therefore, the position and architecture of the branches along the polymer main chain are the main factors that control the rheology of the material.

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From dynamic moduli to molecular weight distribution: A study of various polydisperse linear polymers

Cited by 81 publications

References 0 publications

Molar Mass and Molecular Weight Distribution Determination Of UHMWPE Synthesized Using a Living Homogeneous Catalyst

Molar Mass and Molecular Weight Distribution Determination Of UHMWPE Synthesized Using a Living Homogeneous Catalyst

Analytical Rheology of Polymer Melts: State of the Art

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

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