Correlating mooney viscosity to average molecular weight

Copolymers of styrene and butadiene of the same chemical conposition, but widely different molecular weight distributions, were characterized by gel permeation chromatography. A very good correlation was obtained between the logarithm of the Mooney viscosity and the logarithm of the geometric mean of the number‐ and weight‐average molecular weights. Instead of this molecular weight average, one can equally well use the very convenient “Av log M,” which is a weight‐average molecular weight, using a logarithmic molecular weight scale. This correlation makes it possible to predict the Mooney viscosity from GPC data with a precision of about 15% (± one standard deviation), independent of the molecular weight distribution of the polymer. The obtained correlation was much better than with either weight‐average molecular weight or viscosity‐average molecular weight with α = 0.67.