Homo-polymerization of α-Olefins and Co-polymerization of Higher α-Olefins with Ethylene in the Presence of CpTiCl₂(OC₆H₄X-p)/MAO Catalysts (X = CH₃, Cl)

Cyclopentadienyl-titanium complexes containing –OC₆H₄X ligands (X = Cl,CH₃) activated with methylaluminoxane (MAO) were used in the homo-polymerizationof ethylene, propylene, 1-butene, 1-pentene, 1-butene, and 1-hexene, and also in co-polymerization of ethylene with the α-olefins mentioned. The -X substituents exhibitdifferent electron donor-acceptor properties, which is described by Hammett’s factor (σ).The chlorine atom is electron acceptor, while the methyl group is electron donor. Thesecatalysts allow the preparation of polyethylene in a good yield. Propylene in the presenceof the catalysts mentioned dimerizes and oligomerizes to trimers and tetramers at 25oCunder normal pressure. If the propylene pressure was increased to 7 atmospheres,CpTiCl₂(OC₆H₄CH₃)/MAO catalyst at 25^oC gave mixtures with different contents ofpropylene dimers, trimers and tetramers. At 70^oC we obtained only propylene trimer.Using the catalysts with a -OC₆H₄Cl ligand we obtained atactic polymers with Mw182,000 g/mol (at 25^oC) and 100,000 g/mol (at 70^oC). The superior activity of theCpTiCl₂(OC₆H₄Cl)/MAO catalyst used in polymerization of propylene prompted us tocheck its activity in polymerization of higher α-olefins (1-butene, 1-pentene, 1-hexene)and in co-polymerization of these olefins with ethylene. However, when homo-polymerization was carried out in the presence of this catalyst no polymers wereobtained. Gas chromatography analysis revealed the presence of dimers. The activity ofthe CpTiCl₂(OC₆H₄Cl)/MAO catalyst in the co-polymerization of ethylene with higher α-olefins is limited by the length of the co-monomer carbon chain. Hence, the highest catalyst activities were observed in co-polymerization of ethylene with propylene (here a lower pressure of the reagents and shorter reaction time were applied to obtain catalytic activity similar to that for other co-monomers). For other co-monomers the activity of the catalyst decreases as follows: propylene >1-butene > 1-pentene >> 1-hexene. In the case of co-polymerization of ethylene with propylene, besides an increase in catalytic activity, an increase in the average molecular weight M_w of the polymer was observed. Other co- monomers used in this study caused a decrease of molecular weight. A significant increase in molecular weight distribution (M_w/M_n) evidences a great variety of polymer chains formed during the reaction.