NMR studies of local dynamics in side chain thermotropic polymers

4 NMR Studies of Local Dynamics in Side Chain Thermotropic Polymers 

Results obtained from these NMR studies have been compared to data derived from dielectric spectroscopy of the same polymers. In Figs 3.13(a) and (b) are shown the variation of log(Tc ), where is the characteristic time of the motion, as a function of the reciprocal of absolute temperature, T, for PA2,i and PAej. The different relaxation processes observed in the glassy state by the dielectric experiments are shown schematically below  

Of particular interest in this comparison is the jS relaxation, which is ascribed to the reorientation of the side chain about the Carom QOO) bond. Taking into account both the relaxation seen by the dielectric technique and the internal rotation of the terminal phenyl ring about its 

In the liquid crystalline phase, the local 180° jumps of the phenyl ring are augmented by diffusive rotation about the C2 axis by arbitrary angles as evidenced by the substantial narrowing of the NMR spectra. It is interesting to note that these two motional processes can be separated on cooling into the glassy state, where the diffusive rotation is frozen, whereas the 180° jumps persist as thermally activated local motions.  

Selective pulse sequences have been employed to discriminate between the behaviour of the amorphous and crystalline phases. There does not appear any difference in the phenyl flip dynamics either in the amorphous or in the crystalline phase. 

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