Propylene polymerizations in the presence of various monocyclopentadienyltitanium compounds and methylaluminoxanes(MAO) have been investigated. It was found that by substituting methyl group for hydrogen in the cyclopentadienyl ring

the titanocene catalyst affords a polypropylene with increasing molecular weight by one order of magnitude. Residual AlMe 3 content in MAO has an determinative effect on catalytic activity for the propylene polymerization. An excess of AlMe 3 in the catalyst system

such as 25% AlMe3 inMAO

hinders the polymerization by reducing the Ti species to inactive lower valent states.The effects of molar ratio of MAO to Ti complex

polymerization temperature and monomer pressure on catalytic activity and molecular weight of the products are studied in detail.Tbus

atactic polypropylene with the molecular weight range of 20～100×104

much higher than that prepared by unsubstiuted cycloopentadienyltitanium complex has been synthsized by η5-pentamethylcyclopentadienyltitanium tribenzyloxide/MAO catalyst.The atatic polypropylenes exhibit excellent elasticity.