Propylene polymerization was conducted with
ansa-monocyclopentadienylamidodimethyltitanium complexes ([(η
1-
t-BuN)SiMe
2(Cp)]TiMe
2, Cp = C
5Me
4,
1; C
9H
6,
2) in heptane as solvent at 0°C in the presence of dried modified methylaluminoxane (dMMAO), from which free Me
3Al and
iBu
3Al were reduced to
ca. 0.1 mol%. The effects of cyclopentadienyl ligands on propylene polymerization were investigated under atmospheric pressure of propylene in a semi-batch system where the polymerization rate was followed by the amount of propylene consumed. System
2 showed almost the same consumption rate as that of system
1 in the initial stage, but the rate gradually decreased with increasing polymerization time. In contrast, the rate of system
1 gradually increased during the polymerization. The produced polymer in system
1 had high molecular weight (
Mn = 143,600) and relatively narrow molecular weight distribution (
Mw/
Mn = 1.31). Furthermore, the number-average molecular weight of the polymer linearly increased in proportion to the polymer yield with keeping the number of polymer chains constant. Thus, it was found that quasi-living polymerization of propylene proceeded in the
1-dMMAO/heptane system. The
13C NMR measurement of polypropylenes obtained indicated that systems
1 and
2 produced syndiotactic-enriched and isotactic-enriched polymers, respectively.
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