Polymer solutions IX. Molecular weights of polystyrenes from viscosity measurements

Abstract

AbstractA new method of molecular weight determination of polymers from solution viscosities involving one empirical parameter was suggested earlier. The various assumptions of the method have been examined in detail in the case of polystyrene. A linear plot of k″ [η]2 vs. [η] obtained for one sample of the polymer in a number of solvents and solvent mixtures shows that the corresponding ln ηr/C vs. C plots (when extrapolated) meet at a point. The intercept [η]R obtained is identical with the limiting viscosity number at the point of incipient precipitation as well as the limiting viscosity number at the point of incipient precipitation as well as the limiting viscosity number in cyclohexane at 35°C. It has been further shown that except for high molecular weight samples, the In ηr/C vs. C plot in cyclohexane at 34°C. has a zero slope and values of [η]R agree very well with the values of the limiting viscosity number at the Θ temperature. The double logarithmic plot of [η]R and number average molecular weight is very much scattered but when viscosity average molecular weights are used, the requirement of 0.5 value of slope is satisfied showing the departure is mainly due to heterogeneous distribution of molecular weights.