Effects of Post-Added Alcohol Modifiers on Magnesium Ethoxide Support on Ziegler–Natta Catalyst and Propylene Polymerization Performance

In this work, isopropanol, n-butanol and 2-methoxyethanol were introduced as post-added alcohol modifiers after the preliminary formation of magnesium ethoxide particles. The effects of these alcohol modifiers on the structure of magnesium ethoxide supports, Ziegler–Natta catalysts and propylene polymerization performance were systematically explored. The supports and catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and N2 adsorption–desorption, and the bulk propylene polymerization performances of the resultant catalysts were evaluated. The results demonstrate that alcohol modifiers regulate the nucleation and crystal growth of magnesium ethoxide by altering solvent polarity, steric hindrance and coordination capacity toward magnesium ions. Isopropanol-modified magnesium ethoxide exhibits the smallest particle size. Alcohol modification does not change the crystalline phase of magnesium ethoxide, but adjusts the stacking order and crystallinity of its layered structure. After titanation with TiCl4, mesoporous structures are successfully constructed for alcohol-modified catalysts. The catalyst Cat-iPr modified by isopropanol achieves a specific surface area of up to 218.81 m2·g−1. Alcohol modification tends to refine MgCl2 crystallites and introduce structural disorder, as indicated by XRD peak broadening. Although titanium loading decreases slightly upon alcohol modification, the optimized pore structure improves the accessibility of active sites; consequently, all modified catalysts show higher polymerization activity than the unmodified reference catalyst. Isopropanol and n-butanol modification improve the isotactic index, bulk density and crystallization temperature of polypropylene. In contrast, the ether linkage in 2-methoxyethanol may interfere with the stereodirecting coordination, which is plausibly correlated with the reduced isotacticity and crystallization performance of the resulting polypropylene. Alcohol modification appears to facilitate chain-transfer events and decreases the average molecular weight of polypropylene. Isopropanol and n-butanol broaden the molecular-weight distribution, which is beneficial for polymer processability. Owing to the particle replication effect, the polymer products from the modified catalysts contain low fine-powder fractions, satisfying the particle-size requirements for industrial polypropylene production. This alcohol-modification strategy enables directional tuning of the support pore and crystalline structures while preserving macroscopic particle integrity, offering new insights for the development of high-performance magnesium-ethoxide-based Ziegler–Natta catalysts.