Abstract
Ethylene polymerization using Tp*TiMe2(OAr) [Tp* = HB(3,5-Me2-pyrazolyl)3; Ar = O-2,6-Me2C6H3 (2a), O-2,6-iPr2C6H3 (2b)]-cocatalyst systems [cocatalyst: MAO, [Ph3C][B(C6F5)4], or B(C6F5)3 and AliBu3 or Al(n-octyl)3] or[Tp*TiMe(O-2,6-Me2C6H3)]+[MeB(C6F5)3]−·2THF (3a) in the presence of Al alkyls have been explored. The catalytic activity by 2a,b−cocatalyst systems was highly affected by the Al/Ti molar ratios. Ethylene polymerizations by 2a,b−MAO catalyst systems proceeded in a quasi living manner between −30 and 25 °C, whereas certain degree of chain transfer was observed when the polymerizations by 2a,b were conducted in the presence of borate cocatalysts. The activity by the cationic Ti(IV)−methyl complex (3a) in the presence of Al(n-octyl)3 was close to those by 2a−B(C6F5)3−Al(n-octyl)3, AliBu3 catalyst systems and the Mn values in the resultant polymers were close with uniform distributions; the facts clearly indicate that the same catalytically active species play a role in this catalysis.
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