Your email was sent successfully. Check your inbox.

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

Proceed reservation?

Export
Filter
  • Polymer and Materials Science  (67)
  • Acetylcholine receptor
Collection
Keywords
Publisher
  • 1
    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
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    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.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    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
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    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
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    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
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    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
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    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
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Two effects are of outstanding importance for the mechanical behaviour of polymer-additive mixtures, (a) the plasticizer effect and (b) an effect, which we shall refer to as the “β-suppression” effect: Additives can suppress the secondary (β-) relaxations of the polymer. The β-suppression effect is studied on a number of polymers and additives (dynamic mechanical and dielectric measurements), the molecular motions involved are characterized (2H-NMR spectroscopy) and the thermal density fluctuations are measured (SAXS experiments). A model to explain the effect in terms of the free volume fluctuations is presented.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The molecular order and mobility of two liquid-crystalline polyacrylates with phenyl benzoate moieties as mesogenic side groups and (CH2)m spacers (m = 2 and m = 6) were investigated by pulsed 2H NMR. The mesogenic side groups were isotopically labelled at the terminal phenylene ring. In the glassy state the orientational distribution function was characterized from the angular dependence of the 2H NMR line shape of samples macroscopically ordered in their nematic phase by the 8,4 T magnetic field of an NMR spectrometer. It was found to be Gaussian with widths of ± 18,5° and ± 10,5° for the m = 2 frozen nematic and m = 6 frozen smectic system, respectively. The phenylene rings undergo 180° jumps about their local C2-axes in the glassy state. The time-scale of this process, however, was found not to be uniform. Instead, the analysis of 2H NMR line shapes and their intensities as a function of temperature yielded a log-Gaussian distribution with correlation times characteristic of amorphous solids, 2,2 versus 2,5 decades in width and mean activation energy ĒA = 42 versus 47 kJ/mol for the m = 2 and m = 6 system, respectively. The correlation times for the centre of the distribution agree with those obtained by dielectric relaxation measurements of the same systems, suggesting that reorientation of the whole mesogenic group is detected via the phenylene rings.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 10
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Pulsed 2H NMR was used to study the molecular mobility of a polymer model membrane. The polymerizable lipid analogue consists of a quaternary ammonium ion with two C18 alkyl chains and a methacryloyl moiety attached to the hydrophilic head group via an alkyl spacer. The bilayer spacing as obtained from small angle X-ray scattering was found to be 3 nm in the lamellar Lβ gel phase of the monomer and 3,5 nm in the polymer indicating an interdigitated structure. The molecular mobility in both the monomer and the polymer below and above the phase transition Lβ → Lα was investigated by the NMR lineshapes and the transverse relaxation time T2 at five positions of the monomeric unit: a methylene group of the spacer, the head group and three methylene groups of the alkyl chains (1-, 2-, and 7-position). In contrast to the monomer a pronounced motional gradient was observed in the polymer, where the spacer is almost completely immobilized, whereas the mobility in the middle of the hydrophobic chains is largely retained. A quantitative analysis of the NMR lineshapes shows a gradual increase of molecular mobility in the polymer above the phase transition due to an increase in both the jump rate and the number of conformational transitions.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...