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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of inorganic and organometallic polymers and materials 6 (1996), S. 313-324 
    ISSN: 1572-8870
    Keywords: Polydiethylphosphazenes ; mesomorphism ; nuclear magnetic resonance ; Transfer of Populations in Double Resonance (TRAPDOR)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The existence of mesomorphism in polydiethylphosphazene was recently established by MAS NMR and X-ray diffraction characterization. In the present work the mechanism of motion of the ethyl side groups in the high-temperature polymorph tabove 45 C) is identified and compared to the arrangement of side groups in the low-temperature polymorph. For this purpose a few NMR active nuclei (13C,14N, and2H) were exploited to define the side-chain motions occurring at transition. Experiments performed at varying temperatures close to the onset of solid transition suggest the presence of jumps between two conformations in the pretransition state. Rotor-synchronized triple-resonance NMR of the high-temperature phase determined the average distances between the carbons and the nitrogens in the polymorphs. The theoretical prediction of the dipolar interaction between the nuclei supports the hypothesis that ethyl groups can undergo a complete rotation about the P CH2 bond by jumping across a conformational barrier. The mechanism of motion of the ethyl groups must be cooperative and the collapse of the rigid shell around the main chain is described at the transition.
    Type of Medium: Electronic Resource
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  • 2
    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 A study was made of the macrodefect-free (MDF) composite based on aluminate cement and a poly(vinyl alcohol)–poly(vinyl acetate) (PVAc) copolymer by 13C cross-polarization magic-angle-spinning nuclear magnetic resonance. The spectra were run on both the copolymer and the MDF composite in order to observe the atomic environments of the carbon nuclei. An analysis of the intramolecular hydrogen bonds showed a stronger modification in the sample containing CaAl2O4 (CA) than in that containing Ca3Al2O6 (C3A). From the spectra, it was seen that deacetylation had occurred, and that there was interaction between acetate groups and the calcium and aluminium ions. Proton relaxation times both in the laboratory frame, T1(H), and in the rotating frame, T1ρ(H), were exploited for the study of the dimension of the polymer matrix in MDF composites. An extended interphase was identified in the composite containing CA. A comparison with the behaviour of the composite based on silicates Ca3SiO5–PVAc highlights the better mixing of the phases in the MDF composites containing CA.
    Type of Medium: Electronic Resource
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