Characterization of linear low density polyethylene by temperature rising elution fractionation and by differential scanning calorimetry

Karbashewski, Elizabeth; Kale, L.; Rudin, Alfred; Tchir, W. J.; Cook, D. G.; Pronovost, J. O.

doi:10.1002/app.1992.070440307

Cited by 53 publications

(36 citation statements)

References 13 publications

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“…This is, for instance, the case for linear low-density polyethylenes (LLDPEs) produced with heterogeneous-type Ziegler-Natta catalysts. [23][24][25][26] The implications of the latter source of heterogeneity in copolymers will be reported in the near future. 27 2.2.…”

Section: Sequence Statistics Of Copolymersmentioning

confidence: 99%

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Mathot

Frenkel

2003

Macromolecules

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We report a numerical study of crystallization and melting in bulk statistical homogeneous (random), homogeneous (slightly alternating), and heterogeneous (produced in a batch reaction) copolymers formed by crystallizable monomers and noncrystallizable comonomers. In our dynamic Monte Carlo simulations of lattice chains, the current model further assumes that the comonomers cannot move into crystalline regions by sliding diffusion of the chains. We find that both the overall composition and the statistical distribution of the monomers affect the phase-transition temperature, the resulting relative crystallinity, and the crystal morphology. However, the final absolute crystallinity of homogeneous copolymers seems insensitive to these parameters. Intramolecular segregation between monomers and comonomers is accompanied by crystallization, demonstrating the concept of sequence segregation or nanophase separation of statistical copolymers with assembling structures like in thermoplastic elastomers. Moreover, if crystallization of homogeneous copolymers has started but not yet completed on cooling, subsequent heating will show cold crystallization before melting, which can be attributed to insertion-mode lamellar growth. For heterogeneous copolymers, intermolecular segregation occurs on cooling before crystallization. On the basis of our observations, a pair of master melting and crystallization curves for the crystallinity of a statistical copolymer as a function of temperature are suggested to reflect the characteristic of the monomer-sequence-length distribution. This suggestion facilitates the clarification to the kinetic disturbance in local temperature regions and to the principle of some fractionation methods, such as temperature rising elution fractionation (TREF).

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Section: Sequence Statistics Of Copolymersmentioning

confidence: 99%

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Mathot

Frenkel

2003

Macromolecules

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“…Details of the system and data acquisition are reported by Karbashewski and co-workers. 16 The purpose of using this technique was to compare the TREF profile to the DSC curve shape generated by thermal analysis, as well as to investigate the short branching distribution of selected samples.…”

Section: Trefmentioning

confidence: 99%

Reactive processing of LLDPEs in corotating intermeshing twin‐screw extruder. I. Effect of peroxide treatment on polymer molecular structure

Lachtermacher

Rudin

1995

J of Applied Polymer Sci

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SYNOPSISCommercial ethylene-octene linear low-density polyethylene (LLDPE) polymers were reactively extruded with low levels of 2,5-dimethyl-2,5 di( t-buty1peroxy)hexane to modify their molecular structure and processing properties. Peroxide levels were kept low to avoid crosslinking. This article examines the effects of reactive extrusion in a corotating intermeshing extruder. Gel content analyses and examination of extruded thin tapes indicated that the products were gel-free, but line-broadening in high-resolution W -N M R spectra suggested that some crosslinking did occur. Molecular weight distributions were broadened toward higher molecular weights, as expected. SEC estimates of long-chain branching in reacted polyethylenes were consistent with the results of 13C-NMR analyses. Under our extrusion conditions, the products contained about one long branch per number-average molecule. This result and data on changes in carbon-carbon unsaturation indicate that the major chain extension mechanism is an end-linking reaction between terminal vinyls or allylic radicals formed at chain ends and secondary radicals. Both types are produced by hydrogen abstraction on the LLDPE. All long branches originated a t tertiary branch points. Changes in thermal behavior, as measured by DSC analyses, paralleled those observed by temperature-rising elution fractionation (TREF). SEC molecular weight measurements and long-branch determinations by SEC and 13C-NMR can be used to quantify the effects of peroxide treatment on the molecular structure of polyethylenes. DSC and TREF techniques, however, appear to be more sensitive than are SEC or NMR. Relatively minor variations in the degree of mixing and temperature control during reactive extrusion have noticeable effects on the molecular structures of the peroxide-treated LLDPEs. 0 1995 John Wiley & Sons, Inc.

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“…If a detailed analysis of a sample is required, TREF is used to prepare 7-15 fractions and each fraction is then individually characterized by FTIR, SEC, NMR, and DSC. [22][23][24][25][26][27] Moreover, TREF may be coupled online with SEC analysis. 14,[28][29][30] These time and labor consuming analytical procedures could be partially eliminated by the use of a liquid chromatographic separation according to chemical composition or microstructure.…”

Section: Introductionmentioning

confidence: 99%

Characterization of ethylene‐propylene copolymers with high‐temperature gradient adsorption liquid chromatography and CRYSTAF

Macko¹,

Brüll²,

Wang

et al. 2011

J of Applied Polymer Sci

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Blends of linear polyethylene (PE) and isotactic polypropylene (iPP) with different average molar masses and a series of ethylene-propylene (EP) copolymers with different chemical composition as well as blends of PE, Ipp, and EP copolymers were separated using a carbon-column packing (HypercarbV R ) and gradients of 1-decanol or 2-ethyl-1-hexanol ! 1,2,4-trichlorobenzene (TCB). The separation is based on full adsorption of linear PE on the carbon sorbent at temperature 160 C. However, iPP is not adsorbed and elutes in size exclusion mode. The random EP copolymers have been adsorbed in the column packing and separated according to their average chemical composition after application of the gradient starting with alcohol and ending with pure TCB. The elution volumes of the copolymers depended linearly on the average concentration of ethylene in the copolymers. The HPLC elution profiles were correlated with the CRYSTAF elution profiles. In contrast to CRYSTAF, fully amorphous polyolefin samples were separated with the high-temperature adsorption liquid chromatography.

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Characterization of linear low density polyethylene by temperature rising elution fractionation and by differential scanning calorimetry

Cited by 53 publications

References 13 publications

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Phase Transitions of Bulk Statistical Copolymers Studied by Dynamic Monte Carlo Simulations

Reactive processing of LLDPEs in corotating intermeshing twin‐screw extruder. I. Effect of peroxide treatment on polymer molecular structure

Characterization of ethylene‐propylene copolymers with high‐temperature gradient adsorption liquid chromatography and CRYSTAF

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