| 초록 |
In this work, the mechanism of isotacticity in heterogeneous Ziegler-Natta catalytic systems is investigated by means of density functional theory. Four types of model possible for active sites in TiClx/MgCl2 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, i.e., initiation, in propene polymerization was studied, i.e., the energetics regarding formation of complex, transition state and product was determined by using geometry optimization and/or transition state search. The results suggest that the initiation of polymerization on the (100) lateral surface is kinetically faster as well as undergoes thermodynamically more stable pathway than on the (110) surface. Subsequent monomer insertions after the initiation were also investigated for the purpose of elucidating the mechanism of stereospecificity in propene polymerization. |
