2H NMR Study of Deformed Natural Rubber Networks

Abstract

The orientational order generated in a cross-linked elastomer by uniaxial stress is probed with deuterium NMR spectroscopy. Spectra of technical unfilled natural rubber (NR) vulcanisates (cis-1,4-polyisoprene), locally swelled with o-dichlorobenzene-d4, exhibits quadrupolar doublets under elongation, which have an explicit dependence on the extension ratio and cross-link density. A new mechanical device was designed to fit into an NMR probe-head to permit the elongation of the networks in the interior of the magnet without removal of the sample thus avoiding the effect of the relaxation of the network chains after each step of uniaxial elongation and the observation of always the same section of the stretched sample. A molecular model of rubber elasticity was applied to describe the behavior of rubber network in mechanical and NMR experiments.