A novel approach to the determination of the crosslink density in rubber materials with the dipolar correlation effect in low magnetic fields

Abstract

We present a novel NMR approach to the determination of crosslink densities in rubber materials. The method is based on dipolar correlation effect (DCE) on the stimulated echo examined in a series of rubber samples and linear polyisoprene. The parameter evaluated from the echo attenuation curves is the mean-squared dipolar fluctuation associated with anisotropic reorientations of macromolecular backbones. The contributions to the DCE of the constraints due to excluded volume effects and chemical crosslinks are estimated. A strong dependence of the mean-squared dipolar fluctuation on the crosslink density of rubber combined with the simplicity of performing the measurements with inexpensive low-field instruments suggests that the DCE is a useful tool for routine applications. The potential and problems of performing DCE measurements in low-magnetic-field conditions are discussed in detail.