Pulsed NMR studies of elastomers under large deformation

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Abstract
The spin-spin relaxation time T2 for natural rubber (NR) and NR-synthetic low cis-polyisoprene rubber (IR) mixture vulcani-zates with various crosslink density vs under various extension ratios α has been measured by pulsed NMR. The T2 for the sample becomes shorter with increasing α and the dependence of log T2 on α is approximately linear. It is found that the correlation time of the molecular motion is directly related to the extension ratio α Strain-induced crystallinity of NR and IR vulcanizates has been also studied. There appears a distinct short T2 component, indicating crystallization of elastomers under extension. The degree of crystallinity decreases with increasing IR content. These results show that the amount of strain-Induced crystallinity depends strongly on the stereoregularity of the elastomers.