Deuterium NMR of Deuterated Probes Dissolved in Stretched Polyethylene

Deuterium NMR spectra of deuterated organic probes (including benzene-d₆, chloroform-d, acetone-d₆, pyridine-d₅, and o-and p-xylene-d₁₀ dissolved in stretched polyethylene (PE) are reported for two polymer samples, viz., low-density PE and cross-linked middle-density PE. All spectra exhibit quadrupole splittings due to the finite average quadrupole interaction of the various deuterons. Their behavior is typical of ordered systems in which the probe molecules undergo fast diffusion (on the NMR time scale) between different solvation sites such as, e.g., in liquid crystals. The magnitude of the splitting was studied as a function of probe concentration, temperature, and the degree of stretching, λ. The observed quadrupolar splitting of all probes studied is quite small (less than 5% of the solid-state value) and shows a sigmoidal dependence on the probe concentration. For the low-density PE sample the splitting has a perfect linear dependence on the elongation factor. In unidirectionally stretched PE the asymmetry parameter of the quadrupole Hamiltonian η is zero, but in samples stretched successively in two perpendicular directions η ≠ 0.