Abstract
Abstract Glass-forming liquid-crystalline group polymers were investigated by 2H 2D exchange NMR. In oriented systems, the exchange pattern of a single 2D spectrum yields the orientational distribution function with at least as high precision as a full rotation pattern of 1D spectra. In addition, important information about the geometry of the phenyl-flip motion is obtained. The 2D lineshapes are particularly sensitive towards possible slow motion of the flip axis which could be envisaged to fluctuate within the orientational distribution of the mesogenic group. However, the experimental spectra for a frozen nematic and a frozen smectic polysiloxane with an orientational distribution of width ±18·5° and ±12·5°, respectively show no indication of the corresponding features, proving that the flip axis is fixed within ± 3° even after a large number of flips.
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