Residual Couplings and Dynamic Order Parameters

In polymers and in particular in elastomers, molecular dynamics plays an important role and largely determines the mechanical properties. An investigation of segmental motions is thus of prime importance and NMR is a particularly suitable technique for this purpose. 

At temperatures of about 50 k above Tg, which is the more interesting regime for rubbery materials, the motions are rapid enough (tens of kHz) to effectively average the spin interactions. However, they are not fully anisotropic in high-molecular-mass polymers 

4 One-dimensional NMR Studies of Molecular Motions and Dynamic Order 

Transverse relaxation (T2) and line shape analysis has also been the topic of many studies of molecular dynamics in viscoelastic media [12]. It was found to be indicative of 

A powerful technique for the study of orientation and dynamics in viscoelastic media is line shape analysis in deuteron NMR spectroscopy [1]. For example, the average orientation of chain segments in elastomer networks upon macroscopic strain can be determined by this technique [22-31]. For a non-deformed rubber, a single resonance line in the deuterium NMR spectrum is observed [26] while the spectrum splits into a well-defined doublet structure under uniaxial deformation. It was shown that the usual network constraint on the end-to-end vector determines the deuterium line shape under deformation, while the interchain (excluded volume) interactions lead to splitting [26-31]. Deuterium NMR is thus able to monitor the average segmental orientation due to the crosslinks and mean field separately [31]. 

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