Chemical microstructure of the atactic polypropylenes prepared with cyclopentadienyltitanium tribenzyloxide/methylaluminoxane and pentamethylcyclo pentadienyltitanium tribenzyloxide/methylaluminoxane catalysts has been investigated by 13C-NMR spectra.Both catalysts give the polymers with similar stereo structure distributions.A satisfaction of Baernoullian statistics

by mr/(2mm+mr)+mr(2rr+mr)≈1

indicates that the propylene polymerizations are stereochemically obedient to a chain end control.The present polymers are regioirregular and contain a nonnegligible proportion of propylene units arranged in head to head and tail to tail sequences which can be observed in the methine carbon regin of the 13C-NMR spectra.From a statistical analysis of the regiotriad distribution

it was found that polypropylenes with regioblock structure can be produced with the catalysts.Considering a binary copolymerization of 1

2-orientation monomer and 2

1-orientation monomer

the reactivity ratios

r1 and r2

were calculated.The relations of r1>1

r2>1 and r1r2>>1 indicate that the incoming monomers tend to insert into the metalcarbon bonds with the same orientation as the end units.By substituting methyl group for hydrogen in the cyclopentadienyl ring

the titanocene catalyst affords a polypropylene containing shorter regioblocks.The of the regioblocks increases with reducing the polymerization temperature.