| 초록 |
The ethylene-styrene copolymerization reaction with the MAO based constraied geometry catalyst (CGC) is investigated by the density functional theory (DFT). Two kinds of MAO fragments, MAO-t with terminal Cl and MAO-b with bridging Cl, were considered for model systems in order to investigate the effect of MAO on the reaction mechanism in the metallocene catalyzed polymerization. Structures and energetics of reactants, π-complexes, transition states, and products during the insertion of ethylene and/or styrene monomers into the metal-Cα bond of CGC are analyzed using the software DMol3. The relativistic effective core potential (ECP) is used for titanium and all other electrons are treated explicitly. All the degrees of freedom are minimized with no symmetry constraint with respect to energy except for the reaction coordinate. The activated catalyst systems are stabilized by the coulombic interactions between the cationic catalyst part and the anionic MAO part in both of MAO-t and MAO-b models. The insertion of monomer approaching to the center of metal is restricted by the steric hinderance coming from the spatial positioning of the MAO in these catalyst system.
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