Ziegler-Natta catalyst particle size control in propylene/α-olefin (co)polymerizations

This study investigates the influence of particle size of Ziegler-Natta (ZN) catalysts on the micro-structure and properties of related polypropylenes. In this regard, three catalysts were synthesized with different particle sizes (PS) including PS < 25, 25 ≤ PS ≤ 45, and PS > 45 μm, but from the same ingredients. The catalyst characterization involved a wide range of methods including TGA, BET, SEM, EDS, XRD, LPS, and N₂ adsorption-desorption techniques. Next, a series of propylene homopolymers and their copolymers with 1-hexene were prepared using the as-synthesized catalysts, in the presence or absence of H₂ under similar reaction conditions. The synthesized (co)polymers were characterized with DSC, SSA, ¹³CNMR and TREF techniques. The activity was found to increase with decreasing catalyst particle size in both homo- and copolymerization experiments. Furthermore, a catalyst with a larger particle size provided a polymer with a lower isotacticity index, slightly longer meso sequence length, and higher 1-hexene content of about 10.57 %. This affirms the importance of catalyst/support particle size control during the preparation process in industrial polypropylene plants.