Calculation of the quadrupole splitting in 2H NMR spectra of polymeric networks

Abstract

On the basis of current theories of electric quadrupole effects in NMR, we have calculated the quadrupole splitting Δν in 2H NMR spectra for simple models of polymeric networks. We have considered the effect on Δν of several types of anisotropic motions which are rapid on the NMR time scale: segmental motion; rotations of the deuterium-labeled group about an axis which is fixed relative to the polymeric segment (rotations which are independent of other types of motions); spatially restricted random motion of units of the network relative to their average positions. The calculation predicts an inverse proportionality between Δν and the number of segments of the chain connecting two adjacent units of the network. For the considered systems, in contrast to polycrystals, the lineshape should not depend on the electrostatic field asymmetry parameter η which may affect only the magnitude of the splitting Δν. The theory allows us to explain the appearance of an absorption signal of unusual shape in 2H NMR experiments on cross-linked polymers.