Key Role of Catalyst Pore Structure in Rubber Retention and Distribution of High-Impact Polypropylene Copolymer

High-impact polypropylene (hiPP) is produced by catalyzed homopolymerization of propylene, followed by ethylene-propylene copolymerization for in-reactor blending. Achieving control over the retention and distribution of the rubber phase during this process has been a challenging task, relying mostly on empirical approaches. In this study, we synthesized Ziegler-Natta catalysts with diverse pore structures to establish a quantitative relationship between the catalyst and PP pore structures as well as the retention and distribution of the rubber phase in the production of hiPP. We observed a significant correlation between the catalyst and PP pore structures, with the presence of large pores leading to rubber leakage. Furthermore, we identified that the volume of pores within a specific size range and their location within the particles are critical factors influencing rubber retention. These findings make a valuable contribution to enhancing the properties of hiPP through catalyst design.