Theoretical Analysis of the Catalyst

The mechanism of the CpTi-catalyzed styrene polymerization reaction was studied theoretically using the B3LYP density functional method. Three cases of the polymerization were examined, that is, Cp Ii(CH3)(CH(C6H5)CH3), CpTi(CH3)(CH(C6H5)CH3), and Cpri(CH(C6H5)CH3)+ 

All intermediate and transition state structures were optimized without any symmetry constraints. The systematic vibrational analysis was carried out for the identification of the number of imaginary frequencies, and the determination of zero-point energy and Gibbs free energy was performed only for some important intermediates and the migratory insertion transition state of the chain initiation reaction. 

The coordination of the monomer with Ti(lll) is more stable than that with Ti(lV) because the coordination of the vinyl group is fortified by the back donation from the d-orbital to the vinyl group of styrene. The coordination of styrene with the Ti(III) cation is too stable to an insertion reaction. 

The activation energy of the reaction of styrene and Cp Ii(CH3) (CH(C6H5)CH3) is 9kcal/mol and that of styrene and CpTi(CH(QH5)CH3) is 28 kcal/mol. The active site is a neutral trivalent titanium instead of a triva-lent titanium cation with a coordinated phenyl group. MAO or borate are existing near the active site and neutralize the active site to avoid the coordination of the phenyl group. 

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