High-Temperature Gel Permeation Chromatography: Improvement in the Dispersity Characterization of Molecular Weight Distributions of Polyolefins

In addition to the usual, easily measurable parameters that normally characterize molecular weight distributions (MWD) of polymers: Mw, Mn, Mz, Mw/Mn, three other parameters were chosen for their sensitivity to the amount of high, medium, or low molecular weights present in the polymer. These parameters, related to the polydispersity, are of particular interest for improving information on MWD and for dealing with the real shape of the molecular distribution curve. “High molecular weight dispersity” is the polydispersity of a Gaussian curve having the same maximum as the experimental curve and fitting with it, as well as possible, in the high molecular weight zone. The same criteria are applied to medium and low molecular weight dispersities. Using a small computer for determination of parameters, this method is applied to the practical characterization of Natene, a polyethylene, and Napryl, a polypropylene. This method affords precise, detailed comparisons between polymers and can be used to understand the special shapes of distribution curves related to polymer applications.