A series of group IV metallocene complexes such as titanocenes, zirconocenes and hafnocenes possessing ansa-chain are discussed as regio- and stereoselective catalysts for polymerization of propylene or styrene. Isotactic and syndiotactic polypropylenes are produced via primary
cis-addition by the catalytic use of C
2- and C
s-symmetric zirconocenes, respectively. Significantly, syndiotactic polystyrene is produced, in contrast, via secondary
cis-addition even by using C
1-symmetric titanocenes. The reaction mechanism of those polymerizations, the structure of catalytic species and the significant role of methylalumoxane (MAO) are also discussed.
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