| 초록 |
The stereoselectivity and kinetics of catalytic sites for propylene insertion in Ziegler-Natta catalysts were investigated by density functional calculations. For this purpose, complex energy and activation energy for propylene insertion into the catalytic sites were calculated. The analysis of energetics for propylene insertion reveals that the catalytic site I, generated by TiCl3 adsorption on the (110) surface, is non-stereoselective, while the catalytic site II, created by Ti2Cl7 adsorption on the (100) surface, is highly stereoselective. Moreover, the activation energy for the catalytic site II is much lower than that for the catalytic site I by about 4 kcal/mol. From this result, it is concluded that isotactic polypropylene is dominantly synthesized at the catalytic sites formed on the (100) surface of MgCl2 and the polymerization rate of stereoselective catalytic site is faster than that of non-stereoselective site, which agrees well with experimental result. |
