Effect of crosslinking density on the orientational order generated in strained networks: A deuterium magnetic resonance study

Abstract

The orientational order generated in uniaxially strained rubbers is investigated as a function of crosslinking density. This study was carried out on two sets of rubbers; on randomly crosslinked diene networks and on model end-linked silicone rubbers. The degree of orientational order was measured by means of the deuterium n.m.r. technique; the experiments were carried out either on dissolved deuterobenzene as an n.m.r. probe (dienes) or directly on labelled polymeric chains (silicones). The induced order increases with the crosslinking density as predicted by the kinetic description of rubber elasticity. Data are related to the thermodynamics of the networks rather than to their chemical mesh size which does not accurately describe the topological structure of interest. For both sets of samples, the degree of order varies linearly with the corresponding volume fraction of polymer at swelling equilibrium.