AbstractA procedure is described for the measurement of number‐average molecular weight M̄n on a specimen in bulk form, utilizing a dynamic torsion pendulum. For both atactic and isotactic polystyrenes it has been found that the minimum value of the damping logarithmic decrement, δm, (above the glass temperature) is related to an measured osmometrically in dilute solution by M̄n = δ × 105. The M̄v/M̄n ratio can also be estimated directly from the δ vs. temperature curve. A four‐element spring‐and‐dashpot model yields similar 6 vs. T curves when the Williams‐Landel‐Ferry temperataure dependence is assigned to the viscosity of the dashpots.
