The viscosity and self-diffusion coefficient of linear polyethylene.

The viscosity and self-diffusion coefficient were measured for polyethylene samples in the molecular weight range 200 M 120,000. The viscosity eta was determined by capillary flow or in a parallel plate rheometer; the diffusion coefficient was obtained from the attenuation of NMR spin echoes in a pulsed field gradient. The molecular weight dependence of the viscosity at 175C can be described by two power law regions, etaAB (proportional to) M(1.8) below M = 5000 and eta (proportional to) M(3.6) above 5000. The diffusion coefficient on the other hand can be characterized by a single power law D (proportional to) M(-2) above M = 500. Comparisons with molecular theory were made by examining the product etaD. At low molecular weights etaD agrees well with predictions of the Rouse model. At high molecular weights etaD increases with molecular weight approaching the prediction of the reptation model from below.