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

Abstract

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.