Effect of molecular structure on polyethylene melt rheology. II. Shear‐dependent viscosity

The investigation of the effect of molecular structural variables on the melt viscosity of polyethylene was extended to the shear dependent region by application of a reduced variables treatment following, in a formal sense, that of Bueche. Viscosity–shear rate data were obtained for a series of experimentally polymerized linear polyethylene samples having a range of molecular weights and molecular weight distributions as characterized primarily by gel permeation chromatography. These data could be superimposed on a single reduced variables flow curve using parameters which were a function only of temperature, limiting Newtonian viscosity, M̄ w , and M̄ w /M̄ n . The same treatment was successfully applied also to branched (low‐density) fraction data discussed in a previous paper, with additional correction for long‐chain branching. However, different reduced variables curves were obtained for the branched and linear cases.