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  • 1
    Electronic Resource
    Electronic Resource
    Structural morphology and compaction of nascent high-density polyethylene produced by supported catalysts (1991)
    Springer
    Journal of materials science 26 (1991), S. 3171-3179 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The morphologies of three nascent high-density polyethylene (HDPE) powders, polymerized in the gas phase by different catalysts, were investigated using scanning electron microscopy (SEM). Silica-supported catalyst systems comprising TiCl4/MgCl2,bis(triphenylsilyl)chromate andbis(cyclopentadienyl)chromium were found to produce polymers with globular, nodular and worm-like microstructures, respectively. The topographies of the fluff particles are related to the compaction behaviour of the HDPE powders. Long, worm-like strands that protrude from the particles are capable of forming more extensive entanglements than the shorter, nodular structures. The entanglements are the main cause of agglomeration of the particles during their long-term bulk storage. Furthermore, the rate of thermal oxidation is influenced markedly by the polymer microstructure. The microstructure determines the surface area available for oxygen attack. High-resolution SEM combined with low-temperature plasma etching reveals that the worm-like structures consist of folded-chain lamellae that are coiled around a core of extended chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01124659
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of light intensity on the photooxidation kinetics of high-density polyethylene (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2277-2280 
    Details
    ISSN: 0887-624X
    Keywords: polyethylene ; photooxidation kinetics ; light intensity ; oxygen uptake ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080301025
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  • 3
    Electronic Resource
    Electronic Resource
    Photophysics of polymer-bound 2-(2′-hydroxyphenyl)-2H-benzotriazole photostabilizers (1988)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 26 (1988), S. 505-510 
    Details
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1988.140261203
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  • 4
    Electronic Resource
    Electronic Resource
    Photophysics of a sulfonated 2-hydroxyphenylbenzotriazole UV absorber in solution and in polymer substrates (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 1619-1631 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The total absorption spectrum of the UV absorber sodium 2-(2′-hydroxy-5′-methylphenyl) benzotriazole sulfonate (TINS) has been resolved into contributions by two ground-state forms in acetonitrile-water solvent mixtures and hydrogen bonding polymer and protein substrates. These two ground-state species can be assigned to (i) a planar intramolecularly hydrogen bonded form which can undergo the efficient nonradiative energy dissipation process of excited-state intramolecular proton transfer (ESIPT), and (ii) a fluorescent nonplanar species in which ESIPT is effectively prevented. The mole fractions of each contributing conformer in the polymeric substrates have been estimated. In all the polymer systems studied, a significant proportion of the TINS molecules exist in the nonplanar form and thus may not contribute to photostabilization of the substrate. The proportion of nonplanar molecules varied from 11 to 86% in synthetic polymers and 20 to 41% in protein substrates.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080250615
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  • 5
    Electronic Resource
    Electronic Resource
    New approach to the measurement of polymer photooxidation (1987)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 25 (1987), S. 3311-3323 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In an attempt to eradicate many of the problems associated with outdoor and accelerated testing of polymeric formulations, an apparatus was constructed for the sensitive measurement of oxygen uptake into a polymer during its incipient stages of photooxidation. The photooxidation curves of certain HDPE and LDPE formulations demonstrate a first order asymptotic approach to a limiting value which corresponds to the initial number of reactive centers that are available in the material for oxygen attack. An equation for oxygen uptake as a function of time is derived which incorporates the asymptotic value together with a constant whose value reflects the rate at which the asymptote is approached. These parameters are used to calculate the value of the initial quantum yield for oxygen uptake, a quantity which is indicative of the relative photostability of a given formulation. The kinetics parameters obtained from analyses of certain photooxidative curves confirm that the initial rate of photooxidation is proportional to the concentration of polymer hydroperoxide species which are present in the material as a result of oxidation during processing. The removal of these by thermal treatment of the material in an inert atmosphere results in the appearance of an induction period in the photooxidative profile. The experimental results suggest that this method of determining and interpreting photooxidative curves has certain potential for assessing the relative photostabilities of polymeric formulations.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1987.080251211
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of chromium residues on the stability of gas-phase high-density polyethylene produced by supported catalysts (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1873-1889 
    Details
    ISSN: 0887-624X
    Keywords: polyethylene ; catalyst residues ; hydroperoxides ; chromium ; stability ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermo-oxidative stability of high-density polyethylene (HDPE) prepared by silica supported Ziegler-Natta, bis(triphenylsilyl)chromate and bis(cyclopentadienyl)-chromium(II) catalyst systems was examined by chemiluminescence (CL) techniques and thermogravimetric (TG) analysis. In particular, the technique of dynamic CL in nitrogen allows the concentration of polymer hydroperoxides and the relative stability of these to be simultaneously determined. Polymer hydroperoxides in Ziegler-Natta catalyzed HDPE are relatively stable because titanium and aluminum residues are poor pro-oxidants compared with chromium residues. HDPE produced by bis(cyclopentadienyl)chromium(II) has a low intrinsic thermo-oxidative stability due to the chromium-catalyzed conversion of polymer hydroperoxides into degradation products during thermal aging. Concentrations of residual chromium as low as 1 ppm can profoundly affect the oxidative stability of the polymer and exert a much greater influence than either the extent of branching or the degree of unsaturation. The appearance of the silica catalyst support before and after gas-phase polymerization was studied by scanning electron microscopy. During polymerization the silica support shatters and the resulting submicron fragments are dispersed throughout the polymer particles. On exposure of the nascent polymer to the atmosphere, bis(cyclopentadienyl)chromium(II) is converted to a trivalent chromium species which remains associated with the silica substrate. The presence of trivalent chromium in the poisoned chromium catalyst was confirmed by UV/visible spectrophotometry and the nature of the Cr(III) species was investigated by diffuse reflectance Fourier transform infrared (FTIR) spectroscopy. The high surface area of the catalyst residue renders it a powerful pro-oxidant despite its low concentration. © 1992 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1992.080300910
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  • 7
    Electronic Resource
    Electronic Resource
    The application of simultaneous chemiluminescence and thermal analysis for studying the glass transition and oxidative stability of poly(N-vinyl-2-pyrrolidone) (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 287-297 
    Details
    ISSN: 0887-6266
    Keywords: chemiluminescene ; oxidation ; polyvinyl pyrrolidone ; PVP ; glass transition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A computer-controlled chemiluminescence (CL) instrument incorporating a differential scanning calorimeter was used to simultaneously acquire photochemical and enthalpic data for poly(N-vinyl-2-pyrrolidone) (PVP). Samples were subjected to a linear temperature ramp under nitrogen and their luminescence response recorded. The resultant dynamic CL peak is attributable to the decomposition of hydroperoxide groups and the subsequent mutual termination of secondary polymer peroxyl radicals. It is shown that dynamic CL can be used to characterize the level of oxidation in PVP, which in commercial samples, may be partly related to the level of residual polymerization inititor and to the drying process. The temperature at which maximum CL emission occurs correlates with the glass transition temperature (Tg) of the polymer and increases with increasing molecular weight. A marked increase in the Tg of PVP occurs after it is aged in air for 24 h at 120°C. This is due to the loss of adsorbed moisture from the polymer which was confirmed by thermogravimetric analysis. Oxidation profiles of PVP were obtained by plotting the integrated CL peak area as a function of aging time. The profiles are compared with data obtained from isothermal CL and viscosity measurements. Gas perturbation experiments suggest that when drying PVP under nitrogen at elevated temperatures significant populations of longlived macroalkyl radicals are formed which can peroxidize the polymer on exposure to air. © 1993 John Wiley & Sons, Inc.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090310307
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  • 8
    Electronic Resource
    Electronic Resource
    The kinetics of the reduction of methyl viologen and 9,10-anthraquinone-2-sulfonate by the benzopinacol anion (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 689-693 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reduction of methyl viologen (MV2+) and 9,10-anthraquinone-2-sulfonate (AQS) by the benzopinacol anion in 50% (v/v) propan-2-ol/water was investigated spectroscopically. The rate constants for these reactions were found to be 12.9 ± 0.2 and 0.23 ± 0.01 M-1 s-1, respectively. © John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550240802
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  • 9
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    Time of flight mass spectra of ions in plasmas produced by hypervelocity impacts of organic and mineralogical microparticles on a cosmic dust analyser (2003)
    EDP Sciences
    Details
    Publication Date: 2003-10-01
    Print ISSN: 0004-6361
    Electronic ISSN: 1432-0746
    Topics: Physics
    Published by EDP Sciences
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  • 10
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    The effect of metallocene-catalyzed linear low-density polyethylene on the physicomechanical properties of its film blends with low-density polyethylene (2005)
    Springer
    Details
    Publication Date: 2005-02-01
    Print ISSN: 0022-2461
    Electronic ISSN: 1573-4803
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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