Relaxation in solid polymers

Table 3.1 Activation energies for a-relaxation in solid polymers...

For further literature the reader is referred to refs. [393,627,643-646] for NMRI principles, to refs. [393,632] for applications in polymer science and to ref. [637] for applications in food science. McBrierty [647] has given a comprehensive review of spin relaxation in solid polymers. A comparative study of various NMR imaging techniques has been given elsewhere [648,649]. A (dated) comprehensive bibliography on NMRI has also appeared [650]. 

Subsequently, the same technique was used for investigating methyl groups as a source of cross-relaxation in solid polymers such as PS or polycarbonate, [10]. Mirau et al. have also shown that static 2D NOE spectroscopy can be used to measure interchain interactions [11]. 

Williams, G. Molecular Aspects of Multiple Dielectric Relaxation Processes in Solid Polymers. Vol. 33, pp. 59—92. 

In polymers one will often particularly be interested in very slow dynamic processes. The solid echo technique just described is still limited by the transverse relaxation time T being of the order of a few ps at most. The ultimate limitation in every NMR experiment however, is not T but the longitudinal relaxation time T, which for 2H in solid polymers typically is much longer, being in the range 10 ms to 10 s. The spin alignment technique (20) circumvents transverse relaxation and is limited by Tx only, thus ultraslow motions become accessible of experiment. 

Wilkes, G. L. The Measurement of Molecular Orientation in Polymeric Solids. Vol. 8, pp. 91-136. Williams, G. Molecular Aspects of Multiple Dielectric Relaxation Processes in Solid Polymers. Vol. 33, pp. 59-92. 

Relaxation processes in solid polymers are summarised diagrammatically in Fig. 3.14. 

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