Tailor‐made controlled rheology polypropylenes from metallocene and Ziegler–Natta resins

Production of controlled rheology polypropylenes (CRPPs) is practiced industrially by modifying existing commodity Ziegler–Natta resins through peroxide‐induced β‐scission reactions, resulting in materials with controlled rheological properties and accompanying narrower molecular weight distributions (MWDs). In this work, this methodology was studied using both metallocene‐based polypropylenes (mPPs) and Ziegler–Natta‐based polypropylenes (ZN‐PPs). Numerical simulations based on a previously proposed kinetic model indicated that the nature of the starting resin has a significant effect on the control of MWD polydispersity index (PDI) and weight‐average molecular weight ( ${\overline{M}}_W$) of the resulting CRPP. Based on these observations, experiments were carried out to demonstrate the feasibility of producing CRPP with targeted molecular and rheological characteristics. Commercial mPP and ZN‐PP resins were selected to produce CRPP with similar ${\overline{M}}_W$ or melt flow rates (MFRs) but varying PDIs. The rheological properties and MWDs of these materials were evaluated through oscillatory shear and gel permeation chromatography (GPC) measurements and their extrusion behavior was briefly studied and assessed with respect to these properties. POLYM. ENG. SCI., 59:1114–1121 2019. © 2019 Society of Plastics Engineers