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  • Chemistry  (21)
  • LUNAR AND PLANETARY EXPLORATION  (13)
  • Astrophysics
  • Seismology
  • 2000-2004
  • 1990-1994  (35)
  • 1993  (18)
  • 1991  (17)
  • 1
    Electronic Resource
    Electronic Resource
    The effect of processing on rheological and molecular characteristics of a low density polyethylene (1993)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 377-382 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 viscoelastic responses of some molten polymers, and particularly of low density polyethylene (LDPE), are known to vary with processing history. Reasons for the variations include the effects of shear history on morphological states of the polymer, or on its molecular weight parameters. A typical low density polyethylene has been used to test the shear-history dependence concept following a variety of processing steps. The polymer was sheared in single-screw and twin-screw extruders, and in a high speed melter / mixer (Gelimat). Samples also were precipitated from very dilute solutions in trichlorobenzene and in p-xylene. GPC analyses showed that, in general, these procedures did not affect the various moments of molecular weight. An exception was the Gelimat-mixed sample, for which mild reductions in Mn and Mw were noted. In contrast, melt viscosity and elasticity readings, the former from low shear evaluations and the latter from extrudate swelling, were affected by the various procedures. A drop in melt viscosity and in elasticity was observed, being most pronounced for precipitated and twin-screw extruded versions of the LDPE. Reductions also were observed in the specimen sheared in the Gelimat instrument. Following conditioning at the test extrusion temperature (170°C), viscous and elastic responses tended to revert to those of the unsheared control sample, the exception again being the sample sheared in the Gelimat melter / mixer. Of the various mechanisms proposed in the literature to account for transient property changes such as those reported, temporary changes in the degree of chain entanglement appear the most satisfactory explanation. Irreversible alterations in viscoelastic properties may be associated with changes in molecular weights due to processing at high shear.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760330702
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  • 2
    Electronic Resource
    Electronic Resource
    A systematic nomenclature for cascade polymers (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 641-651 
    Details
    ISSN: 0887-624X
    Keywords: cascade polymers ; dendritic polymers ; arborols ; dendrimers ; starburst polymers ; nomenclature ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cascade (dendritic) polymers are discrete, highly branched, monodisperse polymers that possess branching patterns described by a mathematical progression. A systematic nomenclature that accurately represents these molecules is described. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1993.080310307
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  • 3
    Electronic Resource
    Electronic Resource
    The use of cryogenically ground rubber tires as a filler in polyolefin blends (1993)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 166-174 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 effects of cryogenically ground rubber tires (CGT) on some of the mechanical properties of blends with linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) are presented. Precoating the CGT particles with an ethylene-acrylic acid copolymer is shown to overcome most of the deleterious effects of adding CGT to LLDPE, while still retaining composite processability. A blend of 40 wt% EAA coated CGT particles with LLDPE is shown to have impact and tensile strengths that are 90% of those for the pure LLDPE, representing increases of 60 and 20%, respectively, over blends with uncoated particles. Blends of LLDPE with ground tire bladders demonstrate that even better mechanical properties can be obtained with similar large rubber particle size but somewhat better adhesion. For HDPE, however, it is shown that with large rubber particles, moderate adhesion is not sufficient to produce useful composites.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760330307
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  • 4
    Electronic Resource
    Electronic Resource
    Structure-property relationships in a reactively coupled ductile matrix/brittle dispersed phase blend (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 1347-1362 
    Details
    ISSN: 0887-6266
    Keywords: polyethylene/polymethyl methacrylate blends ; reactive polymer blends ; ductile matrix/brittle dispersed phase blend ; instrumented impact testing ; toughening mechanism ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Blends of t-butylaminoethyl methacrylate grafted polyethylene (PE-g-tBAEMA) with methyl methacrylate-methacrylic acid copolymer (PMMA-MAA) and polymethyl methacrylate (PMMA) were prepared in a Banbury type batch mixer. The effects of component proportions and processing conditions on the melt flow index, morphology, impact, and tensile properties of the resulting polymer blends were investigated. The interfacial chemical reaction was studied using Fourier transform infrared (FTIR) technique. It was observed that the melt index of the blends was reduced with increasing melt processing temperature and mixing time, indicating the formation of PE-g-PMMA block copolymer. New IR bands at 1554, 1628, 1800, and 1019 cm-1 were observed only for PE-g-tBAEMA/PMMA-MAA, the reactive blends, but not for PE-g-tBAEMA/PMMA, the nonreactive blend. These IR bands were attributed to the amide, carboxylate anion and methacrylimide formation resulting from the chemical reaction between the secondary amine on the PE-g-tBAEMA/PMMA moiety and the carboxylic acid on PMMA-MAA segment. The morphology of the blends in various compositions was examined using scanning electron microscopy (SEM) and related to their mechanical properties. All of the blends have a domain structure whose morphology is strongly dependent on the concentration of the dispersed phase. Furthermore, the PE-g-tBAEMA/PMMA-MAA reactive blends were shown to have much finer morphology than the corresponding nonreactive blends. For the reactive polymer blends consisting of brittle particles dispersed in the ductile matrices, the PE-g-tBAEMA/PMMA-MAA, impact and tensile result higher than predicted by the additivity rule were observed. The toughening of polyethylene by PMMA was explained by a “cold-drawing” mechanism. The Young's modulus of the blends and the extent of interfacial adhesion were analyzed with Takayanagi and Sato-Furukawa's theories. © 1993 John Wiley & Sons, Inc.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090311010
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  • 5
    Electronic Resource
    Electronic Resource
    Instrumented dart impact evaluation of linear low density polyethylene at controlled impact energy (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 753-763 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: Instrumented impact testing of linear low density polyethylene (LLDPE I) (ethylene and 1-octene copolymer) was carried out using a Rheometrics Drop-Weight Tester (RDT-5000). A method of partial penetration at controlled impact energy was used and developed. The set impact speed was raised step by step in small intervals of 0.25 m/s over a range of 0.76 m/s to 9.14 m/s. The impact deformation profiles of LLDPE I were obtained for a series of specimens impacted at different speeds. The stress states of the LLDPE I during the corresponding impact events were obtained with the instrumented impact tup. By comparing the observed impact profile with the force-displacement trace, the yield point and the initial failure point of LLDPE I were assessed. The point of 100 percent of the maximum load on the force-displacement trace of a total penetration impact was shown to be the yield point. On the basis of the determination of the yield point, a parameter, ductile ratio (D.R.), was redefined to characterize the ductility of polymers. The initial break point of LLDPE I was determined. The effect of specimen thickness and test temperature on the impact properties was investigated.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760311011
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  • 6
    Electronic Resource
    Electronic Resource
    Identification of the in vivo metabolites of the antimalarial arteether by thermospray high-performance liquid chromatography/mass spectrometry (1991)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 20 (1991), S. 609-628 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermospray mass spectra of arteether and 16 of its potential metabolites all showed strong [M + NH4]+ ions and with only a few exceptions these compounds also showed spectral peaks corresponding to [M + NH4 - HOR]+ and [M + H - HOR]+, where OR represents the alkoxy or hydroxy group at the 12-position. A method for quantifying the metabolites was developed in which the plasma was spiked with an internal standard (the propyl ether analog of arteether), extracted using a C-18 solid-phase cartridge, then subjected to thermospray high-performance liquid chromatographic/mass spectrometric analysis using selected ion monitoring and a C-18 reversed-phase analytical column. Following the intravenous administration of arteether (11.6 mg kg-1), the plasma was found to contain 12 metabolites of arteether in the 10-1000 ng ml-1 range 15 min post-injection, and within 60 min two of these metabolites attained higher concentrations than that of the parent compound, while several other of the metabolites attained concentrations similar to the parent compound. The pseudo-first-order half-life of arteether was found to be 10.0 ± 0.6 min, while the apparent half-lives of most of the metabolites were in the 15-30 min range. Nine of these metabolites were identified by comparison to authentic reference standards and the structures of three remaining metabolites were tentatively assigned from their spectral and chromatographic properties. The metabolic pathways leading to these 12 metabolites was a rather complex, multiple-step process, but most of the metabolites arose from an enzymatic oxidation at one of three sites; 3α, 9α, or the CH2 of the side-chain. Conversion of the endoperoxide group to an cyclic ether was not a major pathway. The in vitro antimalarial activity of reference standards of several of the metabolites was determined and all of those tested were found to be active in the low nanogram per milliliter range.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200201006
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  • 7
    Electronic Resource
    Electronic Resource
    Search for nonoxidative, hydrogen-abstracting initiators useful for melt grafting processes (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 48 (1993), S. 1199-1208 
    Details
    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: Using organic peroxide initiators in the melt grafting of monomers containing amino groups onto polyethylenes is known to cause serious discoloration of the resulting polymers. To eliminate the discoloration while preserving the controlled degree of grafting, a nonoxidative and hydrogen-abstracting initiator with appropriate thermal stability is needed. In this study, the hydrogen-abstracting capability of three azo initiators with suitable decomposition rates in the melt grafting temperature ranges was evaluated using polyethylene cross-linking and polypropylene degradation experiments (called “hydrogen-abstracting experiments”). Among the three azo initiators tested, only a phenylazo initiator, 2 - phenylazo - 2,4 - dimethyl - 4 - methoxyl - valeronitrile (V-19), demonstrated strong hydrogen-abstracting capability from polymer backbones. These three azo initiators were used in the melt grafting of 2 - (N, N - dimethylamino) ethyl methacrylate (DMAEMA) and 2-(N-t -butylamino) ethyl methacrylate (tBAEMA) onto a linear low-density polyethylene (LLDPE). In agreement with the results obtained from the hydrogen-abstraction experiments, only V-19 led to a considerable amount of grafting of both DMAEMA and tBAEMA onto LLDPE. As expected, polymers grafted with V-19 showed significantly reduced discoloration compared with those grafted with peroxide initiators. Further examination of the grafting results indicated that the initiator efficieny, defined as the number of grafted monomer units per radical generated from initiator decomposition, was higher with the phenylazo initiator than with peroxide initiators. The hydrogen-abstracting capability of the phenyl free radical generated from the decomposition of V-19 was estimated to be higher than peroxide and methyl free radicals produced in the decomposition of peroxide initiatros. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1993.070480708
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  • 8
    Electronic Resource
    Electronic Resource
    Antisense DNA oligonucleotides I: The use of ionspray tandem mass spectrometry for the sequence verification of methylphosphonate oligodeoxyribonucleotides (1993)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 7 (1993), S. 190-194 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The sequences of synthetically prepared methylphosphonate oligodeoxyribonucleotides have been verified using ionspray tandem mass spectrometry with sample introduction via flow injection. The technique involves the use of product-ion scans from multiply protonated (4+ and 5+) precursors. Among the ions detected are several series of fragments of different charge states that indicate the base sequence of the intact molecule. Oligomers as large as 18 bases have been successfully characterized.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290070305
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  • 9
    Electronic Resource
    Electronic Resource
    Antisense DNA oligonucleotides II: The use of matrix-assisted laser desorption/ionization mass spectrometry for the sequence verification of methylphosphonate oligodeoxyribonucleotides (1993)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 7 (1993), S. 195-200 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has been used to measure accurately the molecular masses of synthetic methylphosphonate oligodeoxyribonucleotides, up to 18 nucleotides in length. A simple method has been developed for the complete sequence verification of these compounds, which are intractable by classical means. Sequencing from the 5′ end of the molecule is possible because of inefficiencies in the synthetic procedure. Complementary information from the 3′ end can be obtained by partial hydrolysis of the methylphosphonate backbone.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290070306
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  • 10
    Electronic Resource
    Electronic Resource
    The application of chemical state AES and SAM to the examination of spray-formed aluminium alloy fracture surfaces (1993)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 20 (1993), S. 589-594 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The fracture surface of a spray-formed Al-5.2Cr-1.4Zr alloy has been examined using AES and scanning Auger microscopy (SAM). Cratered regions of the surface were identified and high-energy resolution AES analysis showed a localized 20 Å thick Al2O3 film to be present in these areas. Chemical-state imaging of the Al fracture surface enabled the local distribution of oxide to be determined. The surface topography was not found to be suppressed using the standard (P—B)/B or (P—B)/(P + B) correction algorithms. This point is discussed with consideration of the electron emission from such highly structured surfaces. The oxide thickness measured from the craters is in good agreement with that previously determined by XPS for powder particles produced in the atomization process. Crater formation is suggested to occur as a result of complete powder particle solidification prior to the particles impacting the substrate/deposit. The localized oxide, revealed by fracture, presents areas of weakness in the unworked material.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740200708
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