Density Functional Study on the Regioselectivity of Styrene Polymerization with an ansa-Metallocene Catalyst

Abstract

The mechanism of regioselectivity of styrene polymerization with a Cp-based ansa-matallocene catalyst (Cp = η5-C5H5) was investigated using density functional theory (DFT). The metallocene catalyst studied in this work, (CH3)2SiCp2Ti(CH3)2, is known to produce polystyrene via the secondary insertion of styrene. A cationic species, SiH2Cp2Ti+−CH3, is used as an activated form of the catalyst for modeling the initiation of styrene polymerization. The results show that primary insertion is more favorable than secondary insertion in the initiation of styrene polymerization, and the most stable product obtained from primary insertion blocks an additional primary insertion of styrene monomer. For propagation of styrene polymerization, secondary insertion is more favorable than primary insertion. If primary insertion occurs during the propagation, the most stable product of the primary insertion blocks again the additional primary insertion of styrene and thus enhances the secondary insertion. The main driving f...