Viscosity slope constants for solutions of nylon 6 and polytetrahydrofuran

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Abstract
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 kSB) was the most reliable. Slope constants (kcalc) calculated according to an expression of Sakai were plotted as a function of α3 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 kθ under θ‐conditions by an extrapolation procedure. Although individual value of kθ 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.

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