Characterization of commercial linear low-density polyethylene by TREF-DSC and TREF-SEC cross-fractionation

Zhang, Mingqian; Lynch, David T.; Wanke, Sieghard E.

doi:10.1002/(sici)1097-4628(20000214)75:7<960::aid-app13>3.0.co;2-r

Cited by 74 publications

(31 citation statements)

References 25 publications

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“…copolymers produced with single-center and multi-center catalysts can be achieved by using two complementary modern fractionation techniques, analytical or preparative temperature-rising elution fractionation, Tref [1][2][3][4][5][6][7][8][9][10][11] and crystallization fractionation, Crystaf. [12][13][14][15] The results of these analyses are mainly dependent on stereoregularity of poly(propylene) and are almost independent of molecular weight.…”

Section: Introductionmentioning

confidence: 99%

Isoselectivity Distribution of Isospecific Centers in Supported Titanium‐Based Ziegler‐Natta Catalysts

Kissin

Chadwick

Mingozzi

et al. 2006

Macro Chemistry & Physics

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Summary: This article describes the quantitative aspects of the isoselectivity distribution of isospecific centers in five supported titanium‐based Ziegler–Natta catalyst systems containing different internal and external organic donors. Highly crystalline poly(propylene) fractions of the polymers (insoluble in o‐xylene at 95 °C) were analyzed by analytical Tref and gel permeation chromatography (GPC) methods. Separation of the Tref curves into the peaks of sterically uniform components (each represented by the Lorentz function) showed that all these “isotactic” poly(propylene) fractions are nonuniform materials. Each highly crystalline fraction contains several distinct components that differ in stereoregularity. The [mmmm] values for different components (which have approximately the same isotacticity in different polymers) range from as high as 0.986–0.993 to much lower values, in the 0.935–0.955 range. The number of Tref components and their relative contents are substantially different for the crystalline fractions of the polymers produced with different catalyst systems; these parameters depend on the nature of the internal and the external electron donors in the catalysts. GPC analysis of the crystalline poly(propylene) fractions showed that each consists of four or five Flory components (the components produced by kinetically uniform active centers) with widely different average molecular weights, from ≈1 × 104 to ≈1.3 × 106. In general, the probabilities of chain transfer reactions for different active centers decrease with the increase in their isospecificity.Resolution of the Tref curve of the highly crystalline fraction of poly(propylene) prepared with catalyst system 3.magnified imageResolution of the Tref curve of the highly crystalline fraction of poly(propylene) prepared with catalyst system 3.

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Section: Introductionmentioning

confidence: 99%

Isoselectivity Distribution of Isospecific Centers in Supported Titanium‐Based Ziegler‐Natta Catalysts

Kissin

Chadwick

Mingozzi

et al. 2006

Macro Chemistry & Physics

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“…The TREF curve can be converted to the short chain branch (SCB) distribution using the calibration curve reported by Zhang. 1 The SCB distribution in Figure 3 shows the bimodal curve with SCB concentration in the range from 5 to 55 branches per 1,000 carbons for all copolymers. The sharp peak of copolymer with a SCB content of less than 3 branches per 1,000 carbons was shown for all copolymers as well as homopolyethylene.…”

Section: Resultsmentioning

confidence: 98%

“…[1][2][3][4] In the copolymerization of ethylene with Dolefins such as 1-butene and 1-hexene with heterogeneous Ziegler-Natta catalyst, the chemical compositional distribution (CCD) in the copolymer chains is of significant importance because it reflects the compositional heterogeneity. The properties of LLDPE are dependent on molecular weight, molecular weight distribution (MWD), comonomer content and CCD.…”

Section: Introductionmentioning

confidence: 99%

“…The properties of LLDPE are dependent on molecular weight, molecular weight distribution (MWD), comonomer content and CCD. 1 Even though molecular weight is also of importance, comonomer content in copolymer and CCD are dominant parameters to determine the final physical and mechanical properties of ethylene-D-olefin copolymers. It has been understood well that heterogeneous Ziegler-Natta catalyst produces ethylene-D-olefin copolymers with a broad CCD due to its characteristic nature of multi active sites.…”

Section: Introductionmentioning

confidence: 99%

“…Temperature rising elution fractionation (TREF) has been employed since it was developed in 1980s, and crystallization fractionation (Crystaf) method has been developed and studied rather recently to investigate CCD of semicrystalline polyolefins in depth. 1,8,9 In this study, ethylene-1-butene copolymers were prepared with SiO 2 -supported TiCl 4 catalyst by changing of 1-butene/ethylene (C 4 /C 2 ) molar ratio in feed, and the resulting copolymers were analyzed with TREF and Crystaf methods to observe the influence of C 4 /C 2 molar ratio in feed on CCD and other parameters including MWD. In addition, TREF and Crystaf analysis were compared to each other with respect to CCD produced with heterogeneous ZieglerNatta catalyst.…”

Section: Introductionmentioning

confidence: 99%

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Chemical compositional distribution of ethylene-1-butene copolymer prepared with heterogeneous ziegler-natta catalyst: TREF and crystaf analysis

Jeon

Yim

et al. 2009

Macromol. Res.

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Ethylene-1-butene copolymers were prepared with SiO 2 -supported TiCl 4 catalyst by changing of 1-butene/ethylene molar ratio in feed, and the resulting copolymers were analyzed using temperature rising elution fractionation (TREF) and crystallization fractionation (Crystaf) methods to investigate the influence of C 4 /C 2 molar ratio in feed on chemical compositional distribution and other parameters such as molecular weight and its distribution. TREF analysis showed that the copolymers had a broad and bimodal chemical compositional distribution (CCD) regardless of the content of 1-butene in the copolymer. The chemical composition was in the range of 5 to 55 branches per 1,000 carbons for all copolymers prepared in the study. Furthermore, the broader CCD was revealed for the copolymers having the higher content of 1-butene. Crystaf analysis did not showed a bimodal CCD for the copolymers having the 1-butene content of less than 5.1 wt%. The lower crystalline part having higher 1-butene content in Crystaf analysis was less than that of TREF analysis.

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Fractionation

Soares

2004

Encyclopedia of Polymer Science and Technology

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Polymer fractionation techniques attempt to fractionate polymers according to specific characteristics of their microstructures as defined by their distributions of molecular weight, chemical composition, comonomer sequence length, tacticity, and long‐chain branching. Because of the heterogeneous nature of polymers, fractionation techniques are essential for understanding structure‐property relationships, polymerization mechanisms and kinetics, and polymer reaction engineering. In this entry, theoretical models to describe the microstructure of polymers are initially reviewed and used as a basis to understand the several polymer fractionation techniques described in the subsequent sections. Batch fractionation methods are covered next, including temperature variation and solvent/nonsolvent fractionation procedures. The recent technique of crystallization analysis fractionation (Crystaf), together with temperature rising elution fractionation (TREF), are reviewed as methods for fractionation by crystallizability. The well‐established technique for molecular weight fractionation by size‐exclusion chromatography (SEC) is covered next, followed by a section on the versatile field flow fractionation (FFF). Large‐scale fractionation of polymers is covered in the section for continuous polymer fractionation (CPF). Mass spectrometry, particularly matrix‐assisted laser desorption ionization coupled with time‐of‐flight analyzers (MALDI‐TOF) is the subject of the next section. Finally, a section in interaction chromatography and some other less general polymer fractionation techniques is followed by the concluding section on cross‐fractionation techniques.

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Characterization of commercial linear low-density polyethylene by TREF-DSC and TREF-SEC cross-fractionation

Cited by 74 publications

References 25 publications

Isoselectivity Distribution of Isospecific Centers in Supported Titanium‐Based Ziegler‐Natta Catalysts

Isoselectivity Distribution of Isospecific Centers in Supported Titanium‐Based Ziegler‐Natta Catalysts

Chemical compositional distribution of ethylene-1-butene copolymer prepared with heterogeneous ziegler-natta catalyst: TREF and crystaf analysis

Fractionation

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