Pseudo-solid spin-echoes

NMR Evidence for Networks Pseudo-solid Spin-echoes... 

The NMR characterisation of polymeric systems requires first the search for the existence of networks. The observation of a time reversal effect, specific to residual spin-spin interactions, gives evidence for the presence of polymeric networks [3]. This property is reflected by so-called pseudo-solid spin-echoes formed by applying a suitable radiofrequency pulse sequence that results in a rotation of the spin operators (Figure 8.3). 

Figure 8.3 Normalised proton transverse relaxation curve recorded from end-linked calibrated chains. Eight pseudo-solid spin-echoes are recorded to illustrate the time reversal effect specific to the presence of any polymeric network...

Figure 2. Pseudo-solid spin-echoes recorded from a polybutadiene solution (0.88 w/w) in toluene at 254 K relaxation ftmction (+) echo origins 0.8 ( ), 1.6 (O), 2.4 ( ) ms.

Characteristic pseudo-solid spin-echoes recorded from polybutadiene are shown in Fig.2 the polymer concentration in deuterated toluene was 0.88 (w/w). The fraction of monomeric units in the ds conformation was 0.96 (M =110,000 g/mol.). 

J. P. Cohen-Addad and R. Vogin, "Molecular motion anisotropy as reflected by a pseudo solid nuclear spin echo Observation of chain constraints in molten cis-1,4-polybutadiene," Phys. Rev. Letters 33, 940-943 (1974). 

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