Influence of the reaction conditions on the Ziegler-Natta catalyzed ethylene polymerization: Kinetics and properties of the resulting polymers

This work conducts an investigation into how the polymerization conditions affect the kinetics of ethylene homopolymerization and the properties of the final polyethylene using a commercially available Ziegler-Natta catalyst with the formula TiCl4/MgCl2. By employing a mathematical model, we estimated the apparent propagation (kp), activation (ka), and deactivation (kd) rate constants under different reaction conditions, including cocatalyst and catalyst concentration, hydrogen/ethylene ratio, and polymerization temperature. Additionally, we examined the properties of the resulting polyethylene products, such as particle size, molecular weight (Mw), melting temperature, and % crystallinity. We found that the trend of polymer particle size was similar to that of the propagation rate constant under the employed polymerization conditions. Our results indicated that parameters enhancing the polymerization rate also increased kp and reduced crystallinity. The quantitative rate constants and polymer characteristics reported in this study provide valuable insights for industrial polyethylene manufacturers, allowing them to fine-tune plant operation conditions and achieve precise control over polymer particle properties. Furthermore, Density Functional Theory (DFT) calculations provided additional insights into the polymerization process, particularly regarding the role of hydrogen as a chain transfer agent and the fundamental significance of MgCl2, emphasizing the need for a minimal-dimensional model to evaluate this role.