Orientational motions of chain segments in natural rubber crosslinked under uniaxial deformation

• Anisotropic natural rubber was prepared by crosslinking under uniaxial constraint.
• Deformation applied during the crosslinking influences segmental motions parmanently.
• Spatial orientation of chains was found in samples crosslinked under deformation.

Natural rubber (NR) film was crosslinked by γ-irradiation under uniaxial extension. The degree of deformation defined as λ′=l′/l0′ (l0′ and l′ being the lengths of relaxed and uniaxially deformed sample, respectively) was constant and equal to 1.50, and the total irradiation dose was 300 kGy. Deuterium NMR spectroscopy, known as an extremely sensitive method to detect anisotropic molecular motions, was applied for the study of dynamic behaviour of polyisoprene chain segments. Perdeuterated cyclohexane was used as deuterium probe. NMR spectra indicate that segmental motions in NR films crosslinked under deformation are anisotropic. Moreover, spectra of NR films stretched in the direction parallel and perpendicular to the direction of deformation applied during the crosslinking process show an intrinsic difference in orientational behaviour of chain segments.