Molecular, thermal and morphological characterization of narrowly branched fractions of 1-octene linear low-density polyethylene: 1. Molecular and thermal characterization

Defoor, F.; Groeninckx, Gabriël; Schouterden, P.; Heijden, Beatrice van der

doi:10.1016/0032-3861(92)90376-8

Cited by 49 publications

(22 citation statements)

References 7 publications

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“…From the published relationship between melting temperature and SCB content, chains that melt at 115°C have approximately 15SCB/1000C. 18 Data in Figure 14 suggest that chains with SCB content at least this high constitute a significant fraction on a weight basis, although they represent a smaller fraction of the crystallinity.…”

Section: Discussionmentioning

confidence: 93%

Heat sealing of LLDPE: relationships to melting and interdiffusion

Mueller

Capaccio²,

Hiltner

et al. 1998

J. Appl. Polym. Sci.

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ABSTRACT:The effect of heat sealing variables (platen temperature and dwell time) on seal strength of a linear low-density polyethylene (LLDPE) was examined. In order to characterize the development of interfacial strength, blown films were heat-sealed for times from 1 to 100,000 s, much longer than the typical sealing times of less than 1 s. The seal temperature ranged from 100 to 130°C. From the differential scanning calorimetry thermogram, the LLDPE was determined to be completely melted at 130°C. Therefore, the films ranged from partially to fully melted when they were heat-sealed. The seal strength was measured in the T-peel configuration, and the peel fracture surfaces were examined in the scanning electron microscope. A temperature of 115°C or higher was required to form a good seal. The strong effect of seal temperature was related to the heterogeneous composition of the LLDPE studied. At 115°C, the lowermolecular-weight, more highly branched chains easily diffused across the interface. Crystallization upon cooling produced connections across the interface. However, because these chains represented a small fraction of the crystallinity and the molecular weight was low, they contributed much less than the full peel strength. Conversely, chains with less branching represented the main fraction of crystallinity (anchors for tie chains) and the highest molecular weights (more entanglements). Only at temperatures at which the higher-molecular-weight, less branched chains began to melt and diffuse across the interface could high peel strengths be achieved.

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Section: Discussionmentioning

confidence: 93%

Heat sealing of LLDPE: relationships to melting and interdiffusion

Mueller

Capaccio²,

Hiltner

et al. 1998

J. Appl. Polym. Sci.

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“…8 This phenomenon occurs when polymer chains of similar crystallizability are chemically compatible and can crystallize together. This is generally observed as lower crystallinity material eluting with higher crystallinity material, giving a potentially false impression of the composition of a polymer.…”

Section: Introductionmentioning

confidence: 99%

Separation of polyolefins based on comonomer content using high‐temperature gradient adsorption liquid chromatography with a graphitic carbon column

Miller

deGroot

Lyons

et al. 2011

J of Applied Polymer Sci

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This report describes the application of a recently developed polyolefin characterization tool based upon gradient adsorption high-temperature liquid chromatography (HT-LC) using a graphitic carbon stationary phase to polyolefin homopolymer and previously unreported copolymer systems. Polyolefin-based materials find utility in a broad range of applications and are differentiated by parameters such as molecular weight and comonomer content. Polymer comonomer distribution is commonly determined by crystallinity-based separations (ATREF, CRYSTAF). These techniques, however, are time consuming. In addition, some semicrystalline polymers undergo cocrystallization, impacting the techniques' universal utility. Adsorption-based HT-LC can ideally overcome the limitations of crystallinity-based separations, shedding new light on the composition of randomly-polymerized polyolefins. In this report the basic separation capability of the adsorption HT-LC technique, using a graphitic carbon column, is demonstrated for poly (ethylene-co-octene) and poly(ethylene-co-propylene) systems and compared with select precipitation/redissolution HT-LC and ATREF results. Select results in this paper are also compared and contrasted to other recent publications on similar separations of polyolefins.

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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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Molecular, thermal and morphological characterization of narrowly branched fractions of 1-octene linear low-density polyethylene: 1. Molecular and thermal characterization

Cited by 49 publications

References 7 publications

Heat sealing of LLDPE: relationships to melting and interdiffusion

Heat sealing of LLDPE: relationships to melting and interdiffusion

Separation of polyolefins based on comonomer content using high‐temperature gradient adsorption liquid chromatography with a graphitic carbon column

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

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