NMR investigation of slow motions in mesomorphic polymers

In Section 3.3 we were interested in the local dynamics of mesomorphic polymers in either their oriented or non-oriented state. However, NMR parameters may also be affected by the long-range orientational fluctuations of the director. Two techniques have recently been proposed to study this collective behaviour in polymer mesophases.  

The first procedure was introduced by Martins et al. It consists of aligning the nematic polymer in the external magnetic field of the NMR spectrometer and then following the lineshape evolution of a monodomain which has been suddenly rotated at a small angle to the static 

In the method proposed by Van der Putten et al for studying ultra-slow director rotation in nematic polymers, the NMR spectrum is monitored while the sample is rotated in the magnetic field of the spectrometer. The rotation speed of the sample container is chosen such that the director orientation follows the container orientation, albeit with a certain lag. By synchronizing the data acquisition with the container orientation, the phase lag is monitored for several hours. Frequencies as low as 10 Hz can be measured precisely. By using this technique values of have been determined for a side chain polysiloxane. They are in good agreement with those measured by other authors on the same material. 

NMR spectroscopy, which has long been recognized as a powerful tool for studying small-molecule liquid crystals, is also a most attractive technique for investigating mesomorphic polymers. As clearly demonstrated by the examples reviewed in this chapter, it is possible to get a detailed insight into orientational and conformational order of the 

Boeffel, C. Spiess, H.W, Side Chain Liquid Crystals PolymerSy Blackie, Glasgow, 1988, Ch. 8. 

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