Search Results - (Author, Cooperation:S. Wunder)

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  1. 1
    Staff View
    Publication Date:
    2015-03-15
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    *Conservation of Natural Resources/economics ; *Ecosystem ; *Environment ; Guidelines as Topic ; Policy
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    Staff View
    Publication Date:
    2016-05-14
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  3. 3
    Staff View
    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 branching patterns formed as a result of crack growth in dimethacrylate resins below their glass transition temperatures looked similar to fractal trees. The skeletons of the patterns were analysed numerically for their topological and geometrical properties. The number of branches, N i , mean branch lengths, N i , and branch angles of a particular order, defined according to the Strahler and inverted Weibel schemes, followed exponential scaling behaviour: N i ∼ (R b )−i and L i ∼ (R l ) i . Using the relationship for the fractal dimension D=In R B /In R L , a value of D=1.4 was obtained for the fracture pattern. Fractal behaviour was also examined by the box-counting method which indicated a power-law dependence of the mass on the box size with fractal dimension exponent D=1.4 in the case of the fracture pattern. However, the mass-shell method for both the fracture pattern and the fractal trees gave an exponential increase of mass with distance from the origin, rather than the power-law behaviour expected for fractals. This was attributed to the fact that branches of different sizes were distributed in restricted regions of space closer to the periphery, rather than uniformly over the whole pattern.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00349671

    Articles: DFG German National Licenses
  4. 4
    Johnson, C. ; Xu, Huizhu ; Wunder, S. L. ; Houlihan, F. M. ; Chin, E.

    Bognor Regis [u.a.] : Wiley-Blackwell
    Published 1992
    Staff View
    ISSN:
    0887-6266
    Keywords:
    polyamic acid esters, thermal elimination of isobutene from ; pyromellitic acid, meta and para di-tert-butyl esters, thermal elimination of isobutene from ; thermal elimination of isobutene from monomers of polyamic acid ester ; Chemistry ; Polymer and Materials Science
    Source:
    Wiley InterScience Backfile Collection 1832-2000
    Topics:
    Chemistry and Pharmacology
    Physics
    Notes:
    An investigation of the kinetics of the thermal elimination of isobutene from the meta and para isomers of the tert-butyl diesters of pyromellitic acid has been carried out using Fourier transform-Raman spectroscopy and mass spectroscopy. These studies indicate that the elimination of the tert-butyl group occurs at a temperature 26°C lower for the meta isomer than for the para isomer; the maximum rate of elimination occurs at 184°C for the former and at 210°C for the latter. Analysis of the Raman spectra of the compounds indicates that this effect results from the better packing arrangement in the para monomer compared with the meta monomer. Formation of pyromellitic dianhydride in the tert-butyl diesters of pyromellitic acid occurred only after formation of the pyromellitic acid; thus it occurred at lower temperatures for the meta isomer. When the meta and para tert-butyl diesters of pyromellitic acid are dissolved at 1% concentration in poly (vinyl acetate), the elimination of isobutene occurs at 173°C for both isomers, indicating that it is the differences in crystal packing which give rise to the 26°C difference in the solid-state samples. For the meta, para, and 50/50 mixed isomers of the tert-butyl esters of oxydianiline/pyromellitic dianhydride polyamic acid, the elimination of the tert-butyl group occurs at the same temperature (177°C). This result indicates that the packing arrangement of the tert-butyl group is disrupted in the polymer chain, so that intermolecular bonding does not hinder thermal deprotection of the tert-butyl group from the polymer. © 1992 John Wiley & Sons, Inc.
    Additional Material:
    11 Ill.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1002/polb.1992.090301212

    Articles: DFG German National Licenses
  5. 5
    Huang, W. X. ; Wunder, S. L.

    Bognor Regis [u.a.] : Wiley-Blackwell
    Published 1994
    Staff View
    ISSN:
    0887-6266
    Keywords:
    FTIR spectroscopy ; acetylene-terminated polyisoimide ; acetylene-terminated polyimide ; isoimide-imide isomerization ; cross-linking reaction ; thermal curing process ; flexibility effect ; cross-linking effect ; rate constant ; Chemistry ; Polymer and Materials Science
    Source:
    Wiley InterScience Backfile Collection 1832-2000
    Topics:
    Chemistry and Pharmacology
    Physics
    Notes:
    The interrelationship between the cross-linking and isoimide-imide isomerization reactions of oligomeric isoimides and imides was investigated using FTIR spectroscopy. It was found that cross-linking of the acetylene units of Thermid IP-600 retarded the local rearrangement of the isoimide to imide conversion of Thermid IP-600 compared with an aniline-terminated analog, decreasing the rate constant by a factor of about 2. The increased flexibility of both the isoimide (Thermid IP-600) and imide (Thermid FA-700) oligomers increased the cross-linking rate of the acetylene end groups by a factor of 4 and 2, respectively, over that of the more rigid imide oligomer (MC-600). With increasing conversion of the isoimide to imide linkages in Thermid IP-600, the kinetic parameters, Eα and in A, for the cross-linking reaction of this oligomer became the same as those for the oligomeric imide, Thermid MC-600. © 1994 John Wiley & Sons, Inc.
    Additional Material:
    10 Ill.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1002/polb.1994.090321207

    Articles: DFG German National Licenses
  6. 6
    Johnson, C. ; Wunder, S. L.

    Bognor Regis [u.a.] : Wiley-Blackwell
    Published 1993
    Staff View
    ISSN:
    0887-6266
    Keywords:
    raman spectroscopy of thermal curing of PMDA/ODA polyamic acids ; polyamic acid, pyromellitic dianhydride/oxydianiline, thermal curing of ; Chemistry ; Polymer and Materials Science
    Source:
    Wiley InterScience Backfile Collection 1832-2000
    Topics:
    Chemistry and Pharmacology
    Physics
    Notes:
    The effect of solvent on the curing reactions of PMDA/ODA polyamic acids has been investigated using Fourier transform (FT)-Raman spectroscopy. Films of different thicknesses were cured by: (1) doctor blading 15% solids solutions onto glass slides, (2) removing all but the bound NMP, and (3) removing all the N-methypyrrolidinone (NMP). The rate of cure and final degree of conversion of the PMDA/ODA polyamic acid to polyimide increased substantially in the presence of NMP, and this effect was attributed to the plasticizing effect of the solvent. Below a critical solvent concentration, which was estimated to be approximately 40% of the NMP concentration in the bound-solvent limit, the rate of imidization slowed down considerably. Comparison of FT-Raman data for PMDA/ODA polyamic acid: (1) in solution in NMP, (2) complexed with NMP in the solid state, and (3) in the solid state after all the NMP had been removed with water, indicated that intermolecular interactions were greatest in the latter case and weakest in solution. Spectra of PMDA/ODA in NMP solution provide strong evidence for binding of NMP to the amide carbonyl in solution. © 1993 John Wiley & Sons, Inc.
    Additional Material:
    15 Ill.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1002/polb.1993.090310608

    Articles: DFG German National Licenses
  7. 7
    Huang, W. X. ; Wunder, S. L.

    New York, NY [u.a.] : Wiley-Blackwell
    Published 1996
    Staff View
    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:
    A dynamic FT-IR method was used to determine the individual curing temperature ranges of the isoimide-imide isomerization and crosslinking reactions of an acetylene-terminated polyisoimide prepolymer. The individual curing temperature ranges of these two types of chemical reactions for the polyisoimide system using differential scanning calorimetry (DSC) were totally overlapped. Using dynamic FT-IR spectroscopy, the curing temperature ranges of the isomerization and crosslinking reactions were clearly separated. The isomerization reaction began at lower temperatures than the crosslinking reaction and was complete when only half of the crosslinking reaction had occurred. The temperature width, ΔT1/2, was twice as great for the crosslinking reaction compared with the isomerization reaction. Activation energies from dynamic FT-IR spectroscopy can be obtained for the two separate reactions, however, for the reactions considered here, the activation energies were similar, 26 kcal/mol for the isomerization reaction and 23 kcal/mol for the crosslinking reaction. © 1996 John Wiley & Sons, Inc.
    Additional Material:
    6 Ill.
    Type of Medium:
    Electronic Resource

    Articles: DFG German National Licenses