Topology‐rheology regression models for monodisperse linear and branched polyethylenes

Abstract

Abstract Several quantitative descriptors of polymer topology—the Wiener number W , complexity index K, and the index of 3‐starness S —were shown to relate well the measured rheological properties of linear and 3‐arm star monodisperse polyethylene samples to their structure. The complexity index K (the substructure count) provided single‐variable models with correlation coefficients r ranging from 0.95 to 0.98 for zero‐shear viscosity, activation energy, and the parameters λ and α from the Cross equation, which describes the shape of the viscosity/shear rate curve. The regression models with two and three topological variables were characterized by r > 0.99 and low standard deviations. The models were used to predict the values of these rheological parameters for branched monodisperse polyethylenes not yet synthesized, thus indicating the potential of this topology‐based methodology for industrial applications. The study also presents a statistical confirmation for the much stronger effect that long‐chain branching has on shear rheology than that of molecular weight. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2648–2656, 2003