The extensional viscosity for aqueous solutions of high molecular weight poly(acrylamide) copolymers and poly(ethylene oxide) homopolymers was measured using a laboratory‐designed screen extensional rheometer. A Bingham model was developed to estimate the average local polymer coil extensional viscosity (η coil ). A strong correlation was found between the measured η coil values and the polymer extensional viscosity predicted by a bead‐spring model. The dilute aqueous solution drag reduction was measured with a rotating disk instrument under conditions minimizing the effects of shear degradation. Extensional viscosity and drag reduction measurements were performed in deionized water and in 0.514 M sodium chloride. The relative drag reduction efficiency values (Δ) in both solvents were found to strongly correlate with measured η coil values. This is the first report of the accurate prediction of drag reduction behavior for a wide range of polymer types in various solvents from the independently measured molecular parameters η coil and [η] C . The often‐used relative drag reduction efficiency expressed as the product of [η] C and Δ can now be replaced by the absolute drag reduction efficiency [η] C η coil .
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Cowan et al. (2001) studied this question.