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)(2)ZrCl2)/methylaluminoxane (MAO) and bis(substituted indenyl)zirconium dichloride ((RInd)(2)ZrCl2)/MAO catalyst at various polymerization temperature. In the case of (RCp)(2)ZrCl2, 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)-(C5H5-n)](2)ZrCl2 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)(2)ZrCl2 (R = non or 2-Me) showed minimum meso sequence ([mmmm]) at 0 degrees 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 In ([m]/[r]) versus 1/T (T = polymerization temperature (K)). (C) 1998 Elsevier Science Ltd. All rights reserved.