Ethylene polymerization and ethylene/1-octene copolymerization using group 4 half-metallocenes containing aryloxo ligands, Cp*MCl 2(OAr) [M = Ti, Zr, Hf; Ar = O-2,6-R 2C 6H 3, R = tBu, Ph]—MAO catalyst systems

Abstract

Effect of the centered metal toward the catalytic activity as well as comonomer incorporation has been explored in ethylene (co)polymerization using a series of Cp*MCl 2(O-2,6-R 2C 6H 3) [M = Ti ( 1), Zr ( 2), Hf ( 3); R = Ph ( a), t Bu ( b), i Pr ( c)] in the presence of methylaluminoxane (MAO) cocatalyst. Complexes 2a, 3a, b were prepared and identified, and the structures for 2–3a, b were determined by X-ray crystallography as a distorted tetrahedral geometry around the metal center. The catalytic activity in ethylene polymerization was affected by the centered metal employed [Ti > Zr > Hf]; the complexes containing 2,6-diphenylphenoxy ligand ( 1–3a) showed higher catalytic activities than the complexes containing 2,6-di- tert-butylphenoxy analogues ( 1–3b). The molecular weights in the resultant polymers prepared by the Zr and the Hf analogues were lower than those prepared by the Ti–Ph ( 1a) and the Ti– i Pr ( 1c) analogues. Although the copolymerizations of ethylene with 1-octene afforded the copolymers with uniform molecular weight distributions (except 1b), both the catalytic activities and the 1-octene incorporation were highly affected by the centered metal employed; the Ti– i Pr analogue ( 1c) seems to be the most suited in terms of both the catalytic activity and the 1-octene incorporation. The attempted copolymerization of ethylene with 2-methyl-1-pentene using 2a, b and 3a—MAO catalysts afforded linear polyethylene.