Diffusion and Melt Viscosity of a Main-Chain Liquid Crystalline Polyether

Tracer diffusion of a semiflexible main-chain liquid crystalline polyether was studied using forward recoil spectrometry. Investigation of the temperature dependence of melt diffusion showed that in the nematic region the tracer diffusion coefficient, D*, was nearly independent of temperature and increased rapidly at the onset of clearing. Similar behavior was observed for the temperature dependence of the melt viscosity. Diffusion coefficients were measured as a function of tracer (M) and matrix (P) molecular weights within the nematic region and as a function of P in the isotropic region. In the nematic, D* was found to scale as M⁻¹P^−2.3. A strong P dependence was also found in the isotropic phase. These results suggest a macroscopically aligned system in the nematic state which diffuses via a constraint release type of mechanism and, upon clearing, undergoes a sharp increase in constraining tube diameter.