Comparison of residual dipolar interactions in uncross-linked and cross-linked natural rubber by high-resolution solid-state NMR spectroscopy

Abstract It is shown that local residual dipolar broadening of protons coupled to 13 C is a sensitive way to observe motional constraints from networks and entanglements in cross-linked and uncross-linked rubber systems. This may be easily obtained from the indirect observation of proton spin system through 13 C resonance in the conditions of slow magic-angle spinning. The method has been used to visualise the changes in the amount of physical constraints induced during mechanical treatment, which precedes the vulcanisation process.