Motional narrowing, incomplete

For all the cases cited above, which represent those data for which a comparison can be presently made, there is a direct connection between the critical molecular weight representing the influence of entanglements on the bulk viscosity and other properties, and the NMR linewidths, or spin-spin relaxation parameters of the amorphous polymers. Thus the entanglements must modulate the segmental motions so that even in the amorphous state they are a major reason for the incomplete motional narrowing, as has been postulated by Schaefer. ( ) This effect would then be further accentuated with crystallization. 

Solid-state 13C NMR spectra of carbon black filled, uncured and sulfur-vulcanised HR were recorded at 22.6 MHz. The line broadening of the filled polymer relative to the unfilled polymer is attributed to incomplete motional narrowing of the NMR lines [53, 54] Incorporation of filler also results in a decrease in the signal-to-noise ratios in the spectra, but fundamentally it does not obscure the qualitative and quantitative nature of the spectra for the moderately cured elastomer systems. 

Transverse relaxation under incomplete motional narrowing conditions in multispin systems can be treated with the aid of the Anderson/Weiss approximation [2]. Precession phase shifts caused by spin interactions with many coupling partners is assumed to be subject to the central limit theorem. That is, the distribution of the local fields i-e., the distribution of the corresponding angular frequency offsets and hence the distri-... 

With incomplete motional narrowing, the transverse relaxation decay obviously reflects fluctuations with rates Qlt that is a range complementary and partly overlapping with that of field-cycling NMR relaxometry. The representation given in Eq. 40 is particularly useful for the distinction of different dynamic components (see also Fig. 18). 

---