A Simplified Comprehensive Kinetic Scheme for Modeling of Ethylene/1-butene Copolymerization Using Ziegler-Natta Catalysts Mostafa Ahmadi,* Mehdi Nekoomanesh, Hassan Arabi Introduction With the discovery of Ziegler-Natta catalysts in the middle of the fifties, the polymer world experienced a great revolution. Nowadays polyolefins, especially polyethylene and poly(propylene), represent the highest fraction of production among all polymer types, with a production rate of millions of tons per year. This high rate of production is not only due to the cheapness of the raw materials but is also the consequence of the ease of processability and the broadness of mechanical and rheological properties that can be obtained. [1] Quantification of the relationship between these properties and the structural characteristics of polymers has been a target since the first appearance of polymer science. [2–4] Structural characteristics of polymers can be predicted by polymerization process modeling. A proper prediction of polymer microstructure through mathematical models combined with quantitative struc- ture properties relationships can construct a valuable control loop that can be used for optimization of operating conditions, development of new polymer grades and improvement of a product’s properties for its end-use application. Polyethylene is produced in almost all types of reactor configurations. While the macro-scale modeling differs in different processes, the micro-scale modeling, which explains the behavior of the catalyst, is not process Full Paper M. Ahmadi, M. Nekoomanesh, H. Arabi Department of Polymerization Engineering, Iran Polymer and Petrochemical Institute, P.O. Box: 14965/115, Tehran, Iran Fax: þ982 1 4458 0021-3; E-mail: m.ahmadi@ippi.ac.ir A simplified kinetic scheme of eythylene/a-olefin copolymerization has been developed by adding reactions responsible for the unusual kinetic behavior to a general mechanism. The estimation of rate constants has been simplified by making physically meaningful initial guesses. Rate constants affecting yield, MWD and comonomer content have been estimated separ- ately. Experiments were designed to investigate the effects of each rate constant independently. The obtained rate constants show that the sites which are responsible for formation of short chains with higher 1-butene content are more active at the beginning of polymerization, while the sites which are responsible for formation of longer chains with lower 1-butene units are more active at the final stages of polymerization. Macromol. React. Eng. 2010, 4, 135–144 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/mren.200900039 135