0000000000876375
AUTHOR
H. W. Spiess
Pseudo-solid echoes of proton and deuteron NMR in polyethvlene melts
The solid echo technique is applied to determining residual dipolar and quadrupolar couplings in molten polyethylene (PE) and deuterated PE, respectively. The residual coupling defined by the square root of the second moment is about 1% of the corresponding quantity in the solid. It increases with molecular weight, and decreases with rising temperature. A theoretical treatment of time dependent residual couplings yields a decay time that is found experimentally to be about 0.1 ms in molten PE, and independent of molecular weight and temperature within our limits of accuracy. The residual coupling is discussed in relation with chain entanglement in PE. Measurements of the spin-lattice and sp…
Structure and Dynamics of Liquid Crystalline Polymers from Deuteron NMR
The molecular structures of thermotropic liquid crystalline polymers, which have been synthesized systematically in recent years, are described according to the model of decoupling the molecular motions of the mesogenic groups and the polymer chain by inserting a flexible spacer. The molecular structure is related to the properties of these systems, e.g., phase transition temperatures, mesophases formed, etc. The structure and mobility of a specific side chain, liquid crystalline polyacrylate with phenyl benzoate as a mesogenic group is investigated by deuteron NMR and compared with the behaviour of low molecular weight analogues selectively deuterated at equivalent positions, i.e., at the …
Molecular dynamics of solid polymers as revealed by deuteron NMR
Pulsed deuteron NMR spectroscopy is described, which has recently been developed to become a powerful tool for studying molecular dynamics in solid polymers. It is shown that by analyzing the line shapes of2H absorption spectra and spectra obtained via solid echo and spin alignment, respectively, both type and timescale of rotational motions can be determined over an extraordinary wide range of characteristic frequencies, approximately 10 MHz to 1 Hz. By applying these techniques to selectively deuterated polymers, motional mechanisms involving different segments of the monomer unit can be monitored. In addition, motional heterogeneities in glassy polymers can be detected. The information a…