Evaluating the molecular weight distribution of ultrahigh molecular weight polypropylene through rheology.

This article investigates the feasibility of determining the molecular weight distribution (MWD) of linear ultrahigh molecular weight polypropylene (UHMWPP) through rheological measurements. By measuring the linear viscoelastic response over a broad frequency range and applying a mixing rule based on the relaxation modulus, the study correlates rheological data with gel permeation chromatography (GPC) results to estimate material parameters specific to polypropylene. Using three lab-synthesized UHMWPP samples with narrow polydispersity for calibration, the authors successfully predict the MWD of UHMWPPs with broad polydispersity and validate the approach on lower molecular weight polypropylene samples. The work demonstrates that rheology, combined with appropriate modeling and parameter estimation, can reliably extract MWD information for UHMWPP, although careful selection of material parameters is necessary due to their dependence on molecular weight and polydispersity.