13C nuclear magnetic resonance study of molecular motions in natural rubber

Abstract

T ₁ and T₂ have been measured at two frequencies and the nuclear Overhauser enhancement at one for the methylene and methine ¹³C n.m.r. signals from natural rubber. They are shown to be highly consistent with the predictions of a “three-τ” model, which assumes two librational modes of motion at different rates and amplitudes, superimposed on a very slow isotropic motion. Also, they are reasonably consistent with a combined libration and reptation model, but inconsistent with all non-librational models.