Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Molecular flexibility of polymethylene molecules: A Raman spectroscopic study (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 166-173 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Raman spectrum in the CH stretching region of molecules containing long alkyl residues shows characteristic features which provide direct information on their molecular flexibility, as probed by the C–H stretching oscillator which vibrates on the picosecond time scale. From their Raman spectra, librational motions of the (CH2)n units can be studied for molecules in the solid and liquid phases. In the latter case, segmental motions must be considered. In this paper, the spectra of hydrocarbons in the solid, liquid and as clathrates in urea and perhydrotriphenylene are studied in terms of their overall mobility. Using molecular dynamical calculations we show the existence of a selective coupling between CH stretchings and skeletal torsions, which is modulated by the collective mobility of the carbon skeleton. In particular, we account for the frequency dependence of the antisymmetic CH stretching mode using a model which allows for selective coupling between this high frequency mode and the low frequency torsional oscillations about the C–C bonds in the chain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455500
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Raman spectroscopic study of the high-pressure phase of polyethylene (1981)
    s.l. : American Chemical Society
    Macromolecules 14 (1981), S. 1024-1030 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma50005a025
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Band broadening of CH2 vibrations in the Raman spectra of polymethylene chains (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3827-3839 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The isotropic and anisotropic linewidths of methylene vibrations in a homologous series of alkanes of increasing chain length have been measured in the liquid state as a function of temperature. The bandwidths of the CH2 symmetric stretching modes, which are in Fermi resonance with overtones of the CH2 bending vibrations, are temperature insensitive over a 200 K interval; this is best explained in terms of a vibrational dephasing mechanism (inhomogeneous broadening) for these modes. In contrast, for the bending and antisymmetric stretching vibrations, significant band broadening occurs over this same temperature interval. In addition, for these modes, both the absolute value of the bandwidth and the relative rate of increase of the bandwidth with increasing temperature, decrease with increasing chain length. These observations are consistent with a reorientational broadening mechanism as the principal bandwidth contribution for these vibrations. Hindered end-over-end rotation of the molecules, which contributes to the band broadening for very low molecular weight alkanes, rapidly becomes too slow to be observable on the time scale of the Raman experiment for the higher molecular weight alkanes and polyethylene. For longer chain lengths, torsional backbone motions coupled to the high frequency antisymmetric stretching modes can account for the breadth of the bands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450903
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Ultrahigh-molecular-weight polyethylene: Raman spectroscopic study of melt anisotropy (1986)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 24 (1986), S. 99-110 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman spectrum of ultrahigh-molecular-weight polyethylene (UHMWPE) has been obtained in the temperature interval 135-208°C, a region where optical anisotropy was observed to exist. On the basis of our spectroscopic evidence, we believe that ordered regions persist in the melt above the calorimetrically determined melting point, and that part of the polyethylene chain is in an enviroment which is similar to that of the orthorhombic crystal. These ordered domains disappear with increasing temperature, but no calorimetric phase transition is associated with this change. We postulate that the very long relaxation times associated with the highly viscous melt keep the polyethylene chains in ordered environments which persist until decreased viscosity at increased temperature allows long-range segmental motion. Our evidence supports the view that the melt anisotropy of UHMWPE arises from oriented slowly melting superheated crystals and not from a smectic liquid-crystalline phase.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1986.180240111
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Surface stress of polydimethylsiloxane networks (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 2391-2396 
    Details
    ISSN: 0887-6266
    Keywords: surface stresses of elastic networks ; modulus ; reduced stress ; polydimethylsiloxane network ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: For thin elastic films of crosslinked polydimethylsiloxane (PDMS), the tensile modulus was found to be an increasing function of reciprocal thickness over the whole range of elongations. PDMS films between 0.052 and 0.018 mm were investigated. With decreasing film thickness, surface properties may be expected to increasingly contribute to the measured modulus. For small elongations, surface tension is expected to have no effect or to decrease the measured modulus compared with that of a bulk sample. If a surface layer with a modulus greater than that of the bulk modulus is assumed to exist, then the observed increase in modulus with decreasing film thickness can be explained. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2391-2396, 1997
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 6
    Electronic Resource
    Electronic Resource
    NMR and FTIR investigation of the solution imidization kinetics of model compounds of PMDA/ODA polyamic ethyl ester (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 34 (1996), S. 435-448 
    Details
    ISSN: 0887-6266
    Keywords: model compound of polyamic ethyl ester ; meta- and para-diethyl-p,p-oxydiphenylene pyromellitamide ; NMR and FTIR methods ; curing kinetics ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Meta- and para-diethyl-p,p-oxydiphenylene pyromellitamide (DOP), the model compounds of the meta and para PMDA/ODA polyamic ethyl ester, were synthesized and characterized by NMR and FTIR spectroscopy. Investigation of the imidization in d6-DMSO solution using NMR and FTIR techniques has shown that both the half imide and imide were formed. Quantitative analysis of the curing rates and degrees of conversion of the isomers in dilute d6-DMSO solution as a function of time under isothermal conditions or as function of temperature at fixed time (1 h) indicated that the kinetics of the ring closure reaction of the meta and para isomers were the same within 10%. This suggests that intrinsic reactivity differences between the isomers do not have much effect on the imidization process and do not account for the differences in rate that have been observed for the meta and para polymers in the solid state. No interconversion between the two isomeric forms occurred below 180°C, as has been observed for polyamic acids and their model compounds. The degree of conversion strongly depended on the reaction temperature and increased quickly after 170°C. The rate constant of the second ring closure reaction was found to be approximately three to four times the rate constant of the first ring closure reaction. © 1996 John Wiley & Sons, Inc.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
  • 7
    Electronic Resource
    Electronic Resource
    Spectroscopic study of α- and β-phase isotactic polypropylene and of atactic polypropylene in solution (1985)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 23 (1985), S. 2043-2057 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman spectroscopy is used to investigate the conformation and packing of isotactic crystalline α-phase polypropylene compared with lower-order β-phase isotactic polypropylene and to study the solution behavior of atactic polypropylene. The high-frequency region of the spectrum is analyzed in light of a normal-mode calculation that takes into account the methyl-group vibrations. This region is sensitive to both chain conformation and packing, and because of the high intensity of the methyl and methylene high-frequency stretching modes, it can be used to probe small changes in intermolecular or intramolecular order. Differences in the thermal behavior between the two solid isotactic polypropylene samples are explained interms of packing defects which exist in the β-phase form. In the solution study, we demonstrate that, for molecules in which bands sensitive to intermolecular interactions exist, as is the case of the methyl and methylene vibrations of polypropylene, spectroscopic techniques can be used to estimate the minimum overlap concentration.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1985.180231006
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Spectroscopic study of α- and β-phase isotactic polypropylene and of atactic polypropylene in solution (1985)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 23 (1985), S. 2635-2636 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1985.180231221
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Light-scattering characterization of poly(ethylene terephthalate) (1985)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 23 (1985), S. 2567-2578 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: By using a closed-circuit filtration system, we have succeeded in clarifying poly(ethylene terephthalate) (PET) dissolved in hexafluoroisopropanol (HFIP). Such static properties as the radius of gyration Rg, the weight-average molecular weight Mw, and the second virial coefficient A2 and such dynamic properties as the translational diffusion coefficient D, or its equivalent hydrodynamic radius Rh, and the second (diffusion) virial coefficient kd were determined for several PET samples of different molecular weights by using light-scattering intensity and linewidth measurements. An empirical relation between Do (or Rh) and Mw was established: Rh = (1.77±0.15)X10-2 Mw+0.58±0.01 with Rh and Mw expressed in units of nanometers and grams per mole, respectively. The empirical exponent αD(ca. 0.58±0.01) is in good agreement with the less precisely determined intrinsic viscosity/molecular weight exponent αη (ca. 0.71±0.02). Several intensity correlation functions were measured very precisely using long accumulation times. A Laplace inversion was performed using the singular-value decomposition technique. The approximate molecular weight distribution (MWD) determined by light-scattering spectroscopy was in reasonable agreement with a completely independent determination of MWD using gel permeation chromatography (GPC). It was interesting to note, though not surprising, that GPC showed emphasis on lower-molecular-weight fractions, while light-scattering emphasized higher-molecular-weight fractions. The agreement further strengthens some complementary aspects of the two techniques.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1985.180231213
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...