METALLOCENE ION-PAIRS - A DIRECT INSIGHT INTO THE REACTION EQUILIBRIA AND POLYMERIZATION BY C-13 NMR-SPECTROSCOPY

The reaction equilibria of Cp(2)Ti(13)CH(3)Cl and Cp(2)Ti(CH3)(2) with AlMe(3) (TMA) and/or methylaluminoxane (MAO) have been investigated by C-13 NMR. Several adducts have been identified. A study of the C-13 90% enriched ethylene polymerization in an NMR tube in the presence of the above catalytic systems, in the most experimentally significant conditions, and a comparison of the NMR data with the catalytic activity have been made as well. It has been shown that: i) some species are side products, inactive for addition ethylene polymerization; ii) active cation-like species such as Cp(2)TiMe(+)Cl .[AlMeO](-)(n) and Cp(2)TiMe(+)Me .[AlMeO](-)(n) are formed in titanocene-MAO systems. Concerning the role of AlMe(3), contained in MAO solutions, it has been shown that: a) AlMe(3) is mainly bound to MAO; b) if some ''free'' AlMe(3) exists in solution it is not the actual cocatalyst in the metallocene-MAO based catalytic systems; c) the amount of AlMe(3) influences either active or inactive species.