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  • Polymer and Materials Science  (21)
  • 1995-1999  (20)
  • 1975-1979  (1)
  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 48 (1997), S. 471-477 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Molecular motions in low molar mass (46200 g mol - 1) poly(diethylsiloxane) (PDES) are studied by 2H NMR. From DSC measurements the existence of the crystalline phases α1, β1 and α2, β2, as well as a pronounced mesogenic phase αm, is clearly established. Based upon calculations of averaged field gradient tensors based on cone models a detailed motional analysis in the different phases has been conducted. At low temperatures the only motion present besides methyl rotation are librations of the ethyl groups with amplitudes below 25°. The motion in the conformational disordered phase is characterized by conformational changes within the side chains, accompanied by occasional rotations through angles larger than 70° within the backbone. The flexibility of the ethyl groups, however, is limited by steric hindrance, prohibiting a full rotation. This situation is observed also in the meso phase where there is an additional rotational degree of freedom around the main chain axis.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Supramolecular structures based on 4-(3,5-dioxo-1,2,4-triazolidin-4-yl) benzoic acid (U4A) units act as effective junction zones in functionalized polybutadienes, resulting in the formation of thermoplastic elastomers. The dynamics on a molecular scale of the phenyl rings have been probed by 2H-NMR. In the polymeric system, there are three spatially separated environments, which are reflected in the mobility of the polar units. Phenyl rings which are incorporated in the structures are either rigid or undergo 180° phenyl flips. The small fraction of free functional groups move isotropically and their mobility is coupled to the dynamics of the polybutadiene matrix. In two model compounds, where the polymer backbone is replaced by a 1-butenyl (tBu-dU4A) or a C12H24-chain (C12-dU4A), the packing of the single molecules is more perfect, resulting in better-defined dynamics of the molecules. The one-dimensional 2H-NMR spectra can be described quantitatively assuming a distribution of correlation times over 3 decades for the C12-dU4A and 2 decades for the tBu-dU4A, respectively. From the average jump rates the activation energies are determined as 101 kJ/mol and 102 kJ/mol. The geometry of the motional processes is defined by the environment in the clusters up to the order-disorder transition temperature as determined by DSC. The two-dimensional spectra of the model compounds show an elliptical exchange pattern, indicating well-defined slow 180° phenyl flips on a time scale of 100 ms up to 3 s.
    Additional Material: 15 Ill.
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  • 5
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dynamic mechanical, 2H NMR and dielectric spectroscopy techniques were used to identify the nature of the local motions involved in the secondary relaxations of a thermotropic aromatic terpolyester prepared from para-hydroxybenzoic acid, hydroquinone and isophthalic acid. Three secondary relaxations, denoted β, γ, and δ, were detected. A β relaxation, pointed out by dynamic mechanical measurements, is quite close to the large amplitude π-flip processes observed by 2H NMR. Correlated motions of the para-substituted rings and adjacent carbonyl groups may also participate in the β process. Then, at lower temperatures, a γ process is detected by both dielectric and dynamic mechanical experiments. It is assigned to small amplitude oscillations of the isophthalic acid units of the HBA33 polymer. At high temperatures, a heavy overlap of broad rate distributions for the β and γ processes observed in the measurements precludes a more detailed analysis. A dielectric relaxation, denoted δ relaxation, is observed at very low temperatures. It likely comes from motions of a very small number of water molecules trapped in the structure of the terpolyester.
    Additional Material: 7 Ill.
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  • 6
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Infrared spectroscopy is used to study the influence of the polarization of the irradiating light and the substrate surface treated with polyimide on the reorientation process of dye-containing liquid-crystalline side-group copolymers. The depolarization of the linearly polarized light on brushed polyimide surfaces affects the reorientation process and as a consequence the irradiation direction becomes the new order axis after irradiation. Relaxation processes are observed after short irradiation times, since a new stable equilibrium state has not been reached. In contrast, complete reorientation, achieving changes in order parameter of 0.9, is observed after long irradiation times. The system is then stabilized in the new orientational distribution and no relaxation processes occur. The relaxation processes can be explained by a combination of matrix response and thermal cis-trans back relaxation of the azobenzene.
    Additional Material: 5 Ill.
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  • 7
    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: Mixtures of two crystalline brominated aromatic flame retardants with a surrounding polymer were studied by differential scanning calormetry, dynamic mechanical analysis (DMA), wide angle X-ray scattering, and solid-state NMR spectroscopy. 1,2-Bis(tet-rabromophthalimide)ethane (I) and decabromodiphenyloxide (II) were evaluated in high impact polystyrene (HIPS). Additive I exhibits all the properties of an inert filler. The crystalline structure with respect to the pure material remains unchanged within the polymer. Concerning the HIPS matrix, a slight rise in the melt viscosity and a reduced impact strenth as compared to the base resin was observed. In contrast, additive II is miscible with the HIPS matrix and dissolves completely. This leads to an increase of the glass transition temperature of the polybutadiene phase as revealed by solid-state NMR spectroscopy and DMA. The impact resistance of the HIPS matrix is less affected by additive II than by additive I. No interactions were noted with the PS phase at températures up to the glass transition. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 8
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Samples of highly syndiotactic poly(propylene) (s-PP) crystallized in a C-pseudo-centered orthorhombic form are here characterized through high resolution solid state 13C NMR sepctroscopy and wide angle X-ray diffraction. The 13C NMR CP MAS (cross-polarization, magic angle spinning) spectra of highly disordered quench-precipitated s-PP samples (with a structure very close to a C-pseudo-centered orthrohombic form) yield additional resonances beside those already reported in the literature for s-PP samples crystallized with the chains in a fully helical \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} (TTGG\rlap{--} )_n $\end{document} conformation (T: trans; G: gauche). From the correlation of 13C NMR CP MAS spectra with the X-ray diffraction profiles recorded at the same temperatures, it is possible to establish that at a given temperature (approximately 100°C, for our samples) a phase transition from the C- to the B-pseudo-centered orthorhombic form starts to occur. Correspondingly, the aforementioned additional resonances in the 13C NMR CP MAS spectra progressively disappear with the onset of the phase transition. These extra resonances are indeed completely absent in the 13C NMR CP MAS spectrum of samles crystallized in the B-pseudo-centered structure. NMR and X-ray diffraction data, according to differential scanning calorimetry, were interpreted with a recrystallization phenomenon; at temperatures below 140°C for our samples, the variously sized C-pseudo-centered orthorhombic crystallites melt and readily re-crystallize in the B-pseudocentered orthorhombic form.
    Additional Material: 6 Ill.
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  • 9
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 13C-CP/MAS-NMR (cross-polarization magic angle spinning), 2D-WISE (wideline separation experiment) and 1H-spin diffusion experiments allow to gain new insight into the structure and dynamics of solid polyelectrolyte-surfactant complexes, a material with pronounced mesophase formation. Experiments were performed on two different complexes of polystyrene sulfonate and octadecyltrimethylammonium or tetradecyltrimethylammonium counterions, PSS-C18 and PSS-C14. The strong mobility differences between the ionic and alkyl phase in the lamellar complex PSS-C18 are reflected in the NMR behavior: in the surfactant tails, a mobility gradient towards the terminal methyl group is observed. This fact as well as a high content of gauche conformations suggest a non-interdigitating morphology of the tails at room temperature. The behavior changes during cooling below an endothermic transition centered at 255 K where a high trans content and a homogenization of the side chain dynamics is observed. We attribute this transition which is invisible in the X-ray experiments to the formation of a highly transoid, interdigitated phase of the surfactant tails which is however not crystallized in a classical sense. 1H-spin diffusion experiments allow to estimate the distance between mobile and immobile regions of the sample. For the complex PSS-C14, the length scale determined by NMR is essentially that of the primary lamellar structure. For PSS-C18, a characteristic length of the density fluctuations within the proposed undulated lamellar structure is estimated.
    Additional Material: 10 Ill.
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  • 10
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Solid-state NMR spin diffusion experiments and two-dimensional (2D) 1H-13C NMR experiments have been used to study the phase structure, mobility and domain sizes of blends of isotactic poly(propylene) (i-PP) and erucamide (ERU), a low molecular weight slip and antiblock additive for i-PP films. The study of the proton line shapes in pure erucamide and i-PP together with their blends reveals the mobility of the two components. The mobility is higher in the blends than in erucamide and i-PP when they are considered separately. In addition, 2D wideline separation (WISE) NMR spectroscopy indicates that erucamide molecules show both low and high mobilities depending on the erucamide content in the blend. By measuring the proton spin diffusion with 1H detection, the microdomain dimensions have been estimated quantitatively. The domain sizes range from approximately 13 nm to 60 nm.
    Additional Material: 13 Ill.
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