Network Structure Analysis by Means of NMR Transverse Magnetisation Relaxation

2 Network Structure Analysis by Means of NMR Transverse Magnetisation Relaxation 

Solid-state NMR magnetisation relaxation experiments provide a good method for the analysis of network structures. In the past two decades considerable progress has been made in the field of elastomer characterisation using transverse or spin-spin (T2) relaxation data [36-42]. The principle of the use of such relaxation experiments is based on the high sensitivity of the relaxation process to chain dynamics involving large spatial-scale chain motion in elastomers at temperatures well above the Tg and in swollen networks. Since chain motion is closely coupled to elastomer structure, chemical information can also be obtained in this way. 

The maximum relative error of this NMR network density determination was estimated to be about 15%-25% [49, 50]. Comparative analysis of the network density measured in the same samples with the aid of the NMR method and other techniques, such as stress- 

1 Tg for a linear, high-molecular-mass PPO, which was prepared from a polypropylene glycol precursor (with a molecular mass of 4000 g/mol) using a chain extender with a chemical structure similar to that of the crosslinker, is -62.5 °C. The Tg was determined from DMA measurements performed at 0.215 Hz [43]. 

A fairly good correlation between the storage modulus and the relaxation rate (1/T2) was observed. Both methods gave similar values for the mean molecular mass of network 

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