Molecular weight distribution of crystalline polypropylene

The molecular weight distribution of several polypropylene samples was studied by the column elution method. With the exception of a lower molecular weight sample, the molecular weight distribution curves were found to be well described by a revised log‐normal function presented by DAVIS et al. The molecular weights Mw and Mn observed by direct measurements for the whole polymers were in good agreement with the corresponding ones calculated from their molecular weight distribution curves according to this function. Moreover, no anomalous relation was found between the solution viscosity and the molecular weight for several unfractionated polymers and their high molecular weight fractions. These results reveal that there exists no long chain branch even in the high molecular weight region, and that the approximation of the distribution pattern by this revised lognormal function sufficiently characterizes polypropylene samples. The values of Mw/Mn of all samples studied were within a narrow range from 6 to 9, and no distinct dependency of the molecular weight distribution on the average molecular weight was observed.