Viscosity slope constants for solutions of nylon 6 and polytetrahydrofuran

Measurements of the viscosity slope constant k were made on solutions of nylon 6 and polytetrahydrofuran under different conditions of temperature, solvent, and molecular weight of polymer; θ‐conditions were included so that the expansion factor α could be determined in each case. The value of k was influenced somewhat by the particular equation employed to derive it, and generally the Schulz‐Blaschke equation (yielding k SB ) was the most reliable. Slope constants ( k calc ) calculated according to an expression of Sakai were plotted as a function of α 3 and were compared with the corresponding curves in terms of experimental values of k . The agreement was moderately good for PTHF but poor in the case of nylon 6. An expression (due to Imai) involving experimental values of k and α was examined in order to establish a unique value of the slope constant k θ under θ‐conditions by an extrapolation procedure. Although individual value of k θ for nylon 6 measured under θ‐conditions were dependent on molecular weight, the Imai plot yielded a unique value of 0.50 and a slope similar in magnitude to that found for other polymer/solvent systems.