ABSTRACT

This review introduces recent results concerning highly efficient olefin polymerization catalysts with nonbridged half-metallocene type group 4B transition metal complexes of the type, Cp’(L)MX₂ [Cp’ = cyclopentadienyl group; L = anionic ligand such as OAr, NR₂, NPR₂ etc.; M = Ti, Zr, Hf; X = halogen, alkyl etc.]. Effect of substituents on both Cp’ and L plays an essential role for exhibiting high catalytic activity for ethylene polymerization, and the catalyst can be thus tuned only by replacing substituents for the desired homopolymerization and/or copolymerization. In addition, the resultant copolymer prepared by using a series of (cyclopentadienyl)(aryloxy)titanium(IV) complex catalysts possessed different microstructure from those prepared by bridged cyclopentadienyl-amide complex catalyst like [Me₂Si(C₅Me₄)(N^tBu)]TiMe₂. Isospecific living polymerization of 1-hexene as well as vinylcyclohexane has been achieved by using zirconium acetamidinate initiator at low temperature.