Copolymerization of Ethylene with tert-Butylethylene Using Nonbridged Half-Titanocene-Cocatalyst Systems
journal contributionposted on 09.06.2009, 00:00 by Fareha Zafar Khan, Kenichi Kakinuki, Kotohiro Nomura
The copolymerization of ethylene with tert-butylethylene (TBE, 3,3-dimethyl-1-butene) using various half-titanocene [Cp′TiCl2X (X = O-2,6-iPr2C6H3, NCtBu2)]-cocatalyst systems has been carried out. The aryloxo-containing half-titanocenes, Cp′TiCl2(O-2,6-iPr2C6H3) (Cp′ = Cp*, tBuC5H4, 1,2,4-Me3C5H2), displayed the capability to bring about TBE incorporation in the presence of MAO as a cocatalyst, while their ketimide analogues, Cp′TiCl2(NCtBu2) (Cp′ = Cp, Cp*, tBuC5H4), could not accomplish TBE enchainment in ethylene/TBE copolymerization. Among aryloxo derivatives, those carrying tert-butyl and trimethyl substituents on the cyclopentadienyl moiety, Cp′TiCl2(O-2,6-iPr2C6H3) (Cp′ = tBuC5H4, 1,2,4-Me3C5H2), exhibited efficient TBE incorporation and moderate catalytic activity in the presence of MAO, affording ethylene/TBE copolymers with relatively high molecular weight and uniform molecular weight distribution. However, the copolymerization conducted by employing constrained geometry catalyst (linked half-titanocene), [Me2Si(C5Me4)(NtBu)]TiCl2, and zirconocene [Cp2ZrCl2]−MAO catalyst systems resulted in polyethylene without TBE incorporation. Furthermore, the copolymerization of 1-hexene (1-Hex) with TBE and vinyltrimethylsilane (VTMS), by (tBuC5H4)TiCl2(O-2,6-iPr2C6H3) and CpTiCl2(NCtBu2)−MAO catalyst systems, indicated a considerably higher reactivity of VTMS. The 1-Hex/VTMS copolymerization has been elucidated to proceed via 1,2-insertion as manifested by the remarkably efficient VTMS enchainment, hence revealing the difference in the reactivity of TBE and VTMS to arise from that in their electronic and/or steric nature.