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  • 1
    Publication Date: 2009-07-14
    Print ISSN: 0024-9297
    Electronic ISSN: 1520-5835
    Topics: Chemistry and Pharmacology , Physics
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  • 2
    Publication Date: 2008-12-23
    Print ISSN: 0024-9297
    Electronic ISSN: 1520-5835
    Topics: Chemistry and Pharmacology , Physics
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 563-570 
    ISSN: 0887-624X
    Keywords: vanadium ; 51V-NMR ; polymerization ; catalysts ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several VOCL3-based ethylene polymerization catalyst precursors were prepared on silica and studied by solid-state 51V-NMR. The structure of the vanadium species in these samples, as determined by 51V-NMR, did not have any significant effect on the resultant polyethylene MI or MWD. This result is significant since conventional wisdom says the attachment of the transition metal to the silica plays a key role in polymer properties. VOCl3 reacted with hexamethyldisilazane-treated silica and with 250°C dried silica results in double attachment of the vanadium to the silica, yet the catalysts which formed had different reactivities and produced polyethylene with different HLMIs. On the other hand, VOCl3 reacted with 600°C dried silica results in single attachment of the vanadium to the silica, yet this catalyst had a similar reactivity and produced polymer properties similar to the doubly attached vanadium on 250°C dried silica. Two theories are offered to explain the lack of correlation between catalyst precursor structure and catalyst performance. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2889-2898 
    ISSN: 0887-624X
    Keywords: long-chain branching ; polymerization ; catalysts ; polyethylene ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polyethylene produced by a vanadium-based polymerization catalyst contains long-chain branching as determined by NMR and rheology, even though the polymer has very low levels of vinyl unsaturation. A new mechanism is proposed for the formation of the long-chain branching, which involves C—H bond activation of the polyethylene backbone through a σ-bond metathesis reaction, followed by ethylene insertion at the new V—C bond. Consistent with the proposed C—H bond activation mechanism, the polymerization catalyst was also found to insert ethylene into the C—H bonds of alkanes such as heptane. A bridged metallocene catalyst was also found to activate C—H bonds of alkanes suggesting this new mechanism may explain the formation of long-chain branching in some metallocene-produced polyethylene. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2889-2898, 1998
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 51 (1994), S. 13-20 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The characterization of short chain branching in polyethylene using transmission FTIR spectroscopy is investigated. Traditional methodologies, using the methyl deformation band for qualitative and quantitative analyses, have recognized shortcomings. The methyl and methylene rocking bands, which are more characteristic of short chain branch type, were found to be more useful. Methyl, ethyl, butyl, isobutyl, and hexyl branches are qualitatively and quantitatively characterized in LLDPE copolymers by FTIR spectroscopy. Methyl branches were characterized by an absorbance at 935 cm-1, ethyl branches at 770 cm-1, butyl branches at 893 cm-1, isobutyl branches at 920 cm-1, and hexyl branches at 888 cm-1. Fourier self-deconvolution was used to resolve overlapping bands for ethyl, butyl, and isobutyl branches. Using calibrations derived for LLDPE copolymers from 13C NMR data, FTIR spectroscopy was also used to characterize LLDPE terpolymers and LDPE resins. The FTIR and NMR data are in qualitative and quantitative agreement. In some cases correction were made to the FTIR results using data obtained from the methyl deformation band. The FTIR technique is less costly and faster than NMR spectroscopy. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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