A viscosity–molecular weight relationship for polydimethylsiloxanes

The relationship of intrinsic viscosity [η] to the weight‐average molecular weight M̄w of polydimethylsiloxane in toluene at 25°C. has been determined. The modified Staudinger equation, [η] = KM̄wa, with K = 2.43 × 10−5 and a = 0.84, describes the relationship for the above polymers in the range of weight‐average molecular weight from 18,900 to 124,500 (as determined by light‐scattering measurements). These constants differ from the values reported by Barry, where K = 2 × 10−4 and a = 0.66 were obtained. The difference is attributed to the fact that Barry dealt with number‐average rather than weight‐average molecular weight.