An Overview of Important Microstructural Distributions for Polyolefin Analysis

Soares, João B. P.

doi:10.1002/masy.200751101

Cited by 50 publications

(26 citation statements)

References 15 publications

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“…Ultimate mechanical properties and crack resistance improve as the length of the side branch increases, possibly because SCB influences morphology and tie-molecule concentration, requiring greater energy to be absorbed to initiate cracks [33]. SCB is usually detected and quantified using analytical techniques like solution differential scanning calorimetry (DSC), temperature rising elution fractionation (TREF), and crystallization analysis fractionation (CRYSTAF) [34][35][36][37][38][39].…”

Section: 21mentioning

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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Section: 21mentioning

confidence: 99%

Analytical Rheology of Polymer Melts: State of the Art

Shanbhag

2012

ISRN Materials Science

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“…Characterization techniques to measure these distributions include high‐temperature gel permeation chromatography (GPC) for MWD, and crystallization‐based techniques and interaction chromatography methods for CCD . Flory's most probable distribution and Stockmayer's bivariate distribution describe the MWD and CCD of ethylene/α‐olefin copolymers made with single‐ and multiple‐site catalysts, and are often applied to explain polyolefin fractionation results with these techniques …”

Section: Introductionmentioning

confidence: 99%

Joint Effect of Poly(ethyhlene‐co‐1‐octene) Chain Length and 1‐Octene Fraction on High‐Temperature Thermal Gradient Interaction Chromatography

Al-Khazaal

Soares

2016

Macro Chemistry & Physics

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High-temperature thermal gradient interaction chromatography (HT-TGIC) fractionates polyolefins based on an adsorption-desorption mechanism. Several factors influence the shape and position of HT-TGIC chromatograms, notably polymer microstructure, analytical conditions, and, to a lesser extent, solvent type. This article investigates the joint influence of chain length and comonomer content of a series of polyethylene and ethylene/1-octene copolymers having similar 1-octene fractions (0-13 mol%) and a wide range of molecular weights on HT-TGIC fractionation. For each series of copolymers having similar 1-octene fraction, the elution peak temperature decreases exponentially and the profiles become increasingly broader below a critical number average chain length value. The authors use Monte Carlo simulation and Stockmayer distribution to explain the observed behavior, finding that no simple correlation exists between ethylene sequences in the copolymers and peak elution temperature, but that there is strong evidence that axial dispersion is responsible for symmetrical broadening of the HT-TGIC profiles. The authors also study the HT-TGIC of binary blends, finding that components with similar 1-octene contents and dissimilar chain lengths tend to increase co-adsorption/co-desorption effects.

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“…In order to investigate the behavior of the individual complexes in the bimodal polymerizations with SS and DS, the LMW phase (Zr) and HMW phases (Cr) in bimodal PEs were investigated. Due to the fact that the immobilized catalysts have partially lost their single‐site feature and the “calibration” for the HMW fraction, it is difficult to use the simple Schulz–Flory equation to deconvolute the HT‐SEC curves . Therefore, the contents of HMW phase are calculated via the equation

f = \frac{M w - M {normalw}_{Zr}}{M {normalw}_{Cr} - M {normalw}_{Zr}},

where M w is the weight‐average molecular weight of bimodal PE from HT‐SEC, M w Cr is the weight average molecular weight of P‐Cr, M w Zr is the weight average molecular weight of P‐Zr and f is HMW phase content of DS and SS produced bimodal PEs.…”

Section: Resultsmentioning

confidence: 99%

Bimodal Ultrahigh Molecular Weight Polyethylenes Produced from Supported Catalysts: The Challenge of Using a Combined Catalyst System

Líu

Bastiaansen

Goossens

et al. 2017

Macro Chemistry & Physics

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Molecular precatalysts complexes (nBuCp) 2 ZrCl 2 (Zr) and (η1:η5-Me 2 NCH 2 CH 2 C 5 Me 4 )CrCl 2 (Cr) have been successfully supported on silica nanoparticles, via a single support (SS) or a double support (DS) strategy. These catalyst systems have been successfully used to produce bimodal polyethylenes with an ultrahigh molecular weight polyethylene content in a single reactor. The SS and DS catalyst systems have been fully evaluated under an identical polymerization condition to assess the challenges in tailoring the molecular weight distribution. The results show that a detrimental interaction exists between Zr and Cr catalysts, part of the Cr catalyst species is deactivated during polymerization in the both DS and SS systems. The detrimental interaction in the DS system is reduced because the catalysts are supported on separate nanoparticles. But, surprisingly the two catalysts in the DS system are still able to "communicate" to each other via cocatalyst-induced catalyst leaching or other potential reasons.

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An Overview of Important Microstructural Distributions for Polyolefin Analysis

Cited by 50 publications

References 15 publications

Analytical Rheology of Polymer Melts: State of the Art

Analytical Rheology of Polymer Melts: State of the Art

Joint Effect of Poly(ethyhlene‐co‐1‐octene) Chain Length and 1‐Octene Fraction on High‐Temperature Thermal Gradient Interaction Chromatography

Bimodal Ultrahigh Molecular Weight Polyethylenes Produced from Supported Catalysts: The Challenge of Using a Combined Catalyst System

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