Copolymerization of Ethylene with tert-Butylethylene Using Nonbridged Half-Titanocene-Cocatalyst Systems

The copolymerization of ethylene with tert-butylethylene (TBE, 3,3-dimethyl-1-butene) using various half-titanocene [Cp'TiCl2X (X = O-2,6-(Pr2C6H3)-Pr-i, N=C'Bu-2)]-cocatalyst systems has been carried out. The aryloxo-containing half-titanocenes, Cp'TiCl2(O-2,6-(Pr2C6H3)-Pr-i) (Cp' = Cp*, 'BuC5H4, 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(N=C'Bu-2) (Cp' = Cp, Cp*, 'BuC5H4), 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-(Pr2C6H3)-Pr-i) (Cp' = 'BuC5H4, 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)(N'Bu)]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 ('BuC5H4)TiCl2(O-2,6-(Pr2C6H3)-Pr-i) and CpTiCl2(N=C'Bu-2)-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.