| 초록 |
In this work, the problem of isotacticity in a heterogeneous Ziegler-Natta catalytic system is dealt with by means of density functional theory. Four type of models proposed as active sites in MgCl2 supported heterogeneous Ziegler-Natta catalysts are examined: TiCl3 or TiCl4 adsorbed onto (110) or (100) surface of MgCl2. The sites formed by adsorption of TiCl4 are predicted to be more stable than those of TiCl3 in both cases of (110) and (100) MgCl2 surface. The reaction pathway of the first monomer insertion in the propene polymerization was studied, i.e., the energetics of the initial complexation, transition state and product were determined by using geometry optimization and/or a transition state search. Then the subsequent monomer insertion, which represents the crucial issue for the formation of a stereospecific polymer chain, was also investigated. The obtained results of our calculation agree well with the available experimental data, which indicates that these kinds of calculations can be used as a skilful approach to study the details of the reaction mechanism. The proposed mechanism of monomer insertion in this study offers an insight to improve the tacticity or reactivity during the isotactic propene polymerization, and to design reactants such as internal donor. |
