Stereochemical control in propylene polymerization with non-bridged metallocene dichloride/methylaluminoxane

Propylene polymerization was carried out with non-bridged bis(substituted-cyclopentadienyl)zirconium dichloride ((RCp)₂ZrCl₂)/methylaluminoxane (MAO) and bis(substituted indenyl)zirconium dichloride ((RInd)₂ZrCl₂)/MAO catalyst at various polymerization temperature. In the case of (RCp)₂ZrCl₂, the pentad meso sequence ([mmmm]) increased with lowering polymerization temperature. The isotactic sequence of polypropylene increased with an increase of formula weight of substituents in the case of mono-alkyl substituted bis(cyclopentadienyl)zirconium dichloride. The number of methyl (Me) substituents in [(CH₃)_n-(C₅H_5-n)] ₂ZrCl₂ effected the stereo control of polymerization of propylene, and one or two Me substitution resulted in higher isotacticity than the usage of non-or full substituted ligands. Lowering polymerization temperature gave higher isotacticity as observed in Cp₂TiCl₂. The (RInd)₂ZrCl₂ (R = non or 2-Me) showed minimum meso sequence ([mmmm]) at 0°C. Chain-end control was predominant for producing the isotactic portion. The stereoregulation energies were evaluated from the stereochemical dyad composition of the obtained polypropylenes by the Arrhenius plot of ln ([m]/[r]) versus 1/T (T = polymerization temperature (K)).