Structure and dynamics in the amorphous region of natural rubber observed under uniaxial deformation monitored with solid-state 13C NMR

Solid-state 13C NMR experiments were performed under uniaxial deformation of natural rubber to investigate the changes in the structural and dynamical behavior of the amorphous region induced by elongation. The structural change was detected as the change in the 13C cross-polarization (CP) chemical shifts and line shapes. In addition, change in the CP 13C peak intensity as a function of time was also observed and was used to monitor the change of the dynamical behavior with time in high resolution. The relationship between 13C CP intensity and molecular dynamics under uniaxial deformation of natural rubber was examined by the 1H magnetization decay behavior in the rotating frame and 1H–13C CP build-up curves. Although the strain-induced crystallization occurred at around 200% strain, the 13C lineshapes showed no significant change in the orientation of the amorphous chains. On the other hand, the molecular dynamics of the amorphous chains was greatly affected even under lower extension, that is, the enhanced mobility of the chains was observed at 30% strain. This enhanced mobility induced by deformation decreased after the deformation was stopped.