The non-Newtonian behavior of commercial linear polyethylene samples and their fractions were studied a t 190OC. The viscosity q versus shear rate 9 curves of whole polymers could be superimposed onto a single master curve despite the variations of their molecular weights and molecular weight distributions. For fractions, however, the same master curve was inapplicable, and the sensitivity of the viscosity to shear rate was found to be greater than those of the whole polymers. The zero-shear viscosities qo of fractions were related to the 3.42 power of the weight-average molecular weight M , as follows: 70 = 2.39 X 10-'5M,3.4e.
For whole polymers, the zero-shear viscosities were found to be considerably higher at the same M , and markedly lower a t the same z-average molecular weight M , than those of the fractions. Thus, it was concluded that 7 0 corresponds to an average of molecular weight between M, and M,. It was found that the molecular relaxation time r is proportional to MZ5.3 for whole polymers and to OM, for fractions. Using these relations it was possible to relate the flow ratio, the ratio of flow rates a t two different shear stresses, with the molecular weight distribution.