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  • 1
    ISSN: 0570-0833
    Keywords: NMR spectroscopy ; NMR spectroscopy ; Polymers ; Analytical methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: NMR spectroscopy is an effective method not only for examining liquid samples but also for characterizing molecular sturcture, order and dynamics in amorphous and ordered solids. Recent developments in the area of solid-state NMR spectroscopy span from model-dependent studies of conventional one-dimensional spectra to the more definitive two-dimensional (2D) spectra which provide more specific information. For example, with 2D-NMR spectroscopy it is possible to determine the orientational distribution functions of molecular segments in drawn polymers and to distinguish different mechanisms of complex molecular motions. Following an introduction to basic NMR spectroscopy, an overview of the current state-of-the-art of 2D methods in solid-state NMR spectroscopy is presented and demonstrated with selected examples.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1435-1528
    Keywords: Key words Fourier-transform rheology ; Viscoelastic polymer solutions ; Non-linear regime ; High sensitivity FT-rheology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract  The application of oscillatory shear strain leads, in the non-linear regime, to the appearance of higher harmonic contributions in the shear stress response. These contributions can be analyzed as spectra in Fourier space, with respect to different frequencies, amplitudes and phase angles. In this article, we present an application of this new characterization method to a solution of the linear homopolymer polyisobutylene. The degree of non-linear response during oscillatory shear is quantified using the normalized intensity of the third harmonic contribution. We were able to show experimentally on polyisobutylene that there is an immediate onset of the non-linear response even for very small shear strain amplitudes.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 13C solid-state NMR spectra of the aromatic polyester 1 with flexible hexadecyloxy side chains are measured at temperatures below and above its solid-solid phase transition in order to study the conformation of the side chains. The signals due to the CH2 carbons reflect the ratio of trans and gauche conformations at the various positions along the chain. An increase in the gauche content was observed towards the end of the side chain in both phases, however, in the low temperature phase the spectra are dominated by all-trans sequences. The solid-solid transition, as detected by differential scanning calorimetry corresponds to a large increase in the gauche content at all positions on the side chain, except near to the rigid polymer backbone. Above the solid-solid transition a small residual concentration of all-trans sequences was detectable.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 189 (1988), S. 2367-2379 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2H NMR is used to study the mobility of the alkylene chain in solid poly[(dimethyliminio)-alkylene]s (α,ω-ionenes) complexed with poly(styrenesulfonate). In 10, 10-ionene the alkylene chain motion was probed on samples selectively deuterated at the 1-, 2-, and 4-position as well as in the methyl part of the quaternary ammonium groups. 2H NMR spectra show that all positions in the polymethylene chains are involved in conformational jumps between trans and gauche states. The mobility of the methylene units adjacent to charged centres was found to be significantly reduced compared with that of units in the inner part of the chain. The charged quaternary ammonium groups themselves, however, do not take part in trans-gauche isomerization. An increase in mobility resulting from increasing the length of the alkylene chains between the charge centres was observed in 3,3-, 6,6- and 10,10-ionene complexes labelled in the 2-position. The differences in chain dynamics were also detected via EPR line shapes of small spin probe molecules incorporated into the complexes.
    Additional Material: 6 Ill.
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  • 6
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The discotic liquid-crystalline polymers poly[oxy(3,7,10,11-tetrapentoxy-2,6-triphenylenediyl)-oxycarbonyltetradecamethylenecarbonyl] (1), containing discotic mesogenic groups in the main chain and poly[methyl(3,6,7,10,11-pentapentoxy-2-triphenylenyloxyundecyl)siloxane] (2) with disc-like groups attached to the polymer chain by flexible spacers, are studied by X-ray diffraction, solid-state nuclear magnetic resonance, differential scanning calorimetry and dynamic mechanical measurements, in order to determine the dynamic and structural transitions. It is shown that low-temperature softening in both polymers is caused by the mobility of short aliphatic side chains attached to the discotic units. Once formed, the columnar mesomorphic structure is stable up to the temperature of isotropization. For the main-chain polymer, a third transition is observed in samples quenched from the melt. The transition is related to the mobility of the main chain in an amorphous structure, where the discotic units are not organized in columns.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Forced Rayleigh scattering was used to investigate the dynamics of photoinduced isomerization of azobenzene involved in reversible holographic information storage. The studies were performed with statistical liquid-crystalline side-group copolymers having different concentrations of the dye, in a copolymer forming no mesophase and in a physical mixture of the dye in a liquid-crystalline side-group homopolymer. Two relaxation processes were found in the glassy state of these polymers, the faster one being distributed over a wide range of relaxation times ascribed mainly to reorientational relaxation of the dye as well as the glassy matrix. The second is a single exponential, ascribed to the relaxation of azobenzene back to its trans conformation. The two processes could be assigned through a control experiment using an irreversibly isomerizing dye. The results of a calculation of the angular dependence of azobenzene isomerization was compared with the experiment, in order to judge the influence of the anisotropic matrix on the relaxation process.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The molecular mobility at the elastomer/active filler interface is studied in Aerosil-filled poly(dimethylsiloxane) networks. It is shown that in unstrained samples two regions of different local chain mobility can be distinguished, namely chain units in the adsorption layer and outside of it. The fraction of chain units with relatively low mobility in the adsorption layer is estimated. In a uniaxially strained sample, immobilization of chain units near the filler surface is observed at temperatures up to 20 K above the melting temperature of an unstrained sample. The network structure of unfilled and filled networks is probed by analysis of the quadrupolar splitting in 2H solid-echo spectra of uniaxially strained samples. The local chain order at a given elongation is larger by a factor of 1,5-2 in the filler system. This is interpreted in terms of an increased number of effective cross-links and the differences between macroscopic and microscopic strains.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 4-(4-Carboxyphenyl)-3,5-dioxo-1,2,4-triazolidin-1-yl moieties resulting from 4-(3,5-dioxo-1,2,4-triazolin-4-yl)benzoic acid (U4A) randomly attached to 1,4-polybutadiene form supramolecular aggregates which act as effective junction zones in new thermoplastic elastomers. Deuteron nuclear magnetic resonance (2H NMR) spectroscopy was used to investigate the molecular dynamics of the polymer backbone and the junction zones in selectively labelled samples. The spectra show motional heterogeneity along the polymer chain as well as in the supramolecular domains. Polybutadiene segments which are adjacent to these polar clusters are restricted in their mobility, even at temperatures 100 K above the glass transition temperature Tg. The immobilized regions are estimated to involve about two monomeric units. The functional groups in the supramolecular structures are rigid or exhibit 180° -phenyl flips dependent on their location in the middle or in the edges, respectively. Polar units which are not enclosed in the clusters and dispersed in the polymer matrix undergo fast isotropic motions.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2D NMR spectra have been measured at variable temperatures between -100°C and +110°C in a sample of melt crystallized deuterated polyethylene (PE). The line shape could be decomposed into a central part originating from deuterons in the amorphous regions and outer parts from crystalline regions of PE. The “NMR crystallinity” determined from this separation was 72% in agreement with the X-ray crystallinity of 74%. Changes of the crystalline NMR line shape were interperted in terms of oscillations around the chain axis, the r.m.s. oscillation amplitude varying from 5° at 40°C to 12° at 110°C. The central part of the NMR line shape indicates the existence of a “narrow” and a “medium” component due to different motional processes in the amorphous regions.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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