Ethylene/styrene copolymerization by various (cyclopentadienyl)(aryloxy)titanium(IV) complexes-MAO catalyst systems

Copolymerizations of ethylene with styrene by various (cyclopentadienyl)(aryloxy)titanium(IV) complexes of the type Cp'TiCl₂(O-2,6-ⁱPr₂C₆H₃) [Cp' = ^tBuC₅H₄ (2), 1,3-Me₂C₅H₃ (3), 1,2,3-Me₃C₅H₃ (4), 1,2,4-Me₃C₅H₃ (5)] have been explored in the presence of methylaluminoxane (MAO) as the cocatalyst. Effect of cyclopentadienyl fragment was explored and the catalytic activity increased in the order 3, 4 > 2 > 5, suggesting that effects of both electronic and steric bulk play an essential role for the copolymerization. Resultant polymers by these catalyst systems were poly(ethylene-co-styrene)s exclusively in all cases, and the use of 4 was quite effective for preparing relatively high molecular weight polymer with unimodal molecular weight distribution as well as with efficient styrene incorporation. The styrene incorporation efficiency did not strongly depend upon the cyclopentadienyl fragment used, and this is somewhat different from those obtained by the linked cyclopentadienyl-amide titanium catalyst [Me₂Si(C₅Me₄)(NR)]TiCl₂ [R = tert-Bu (6), cyclohexyl (7)]. The resultant copolymers possessed unimodal comonomer distributions (single composition) confirmed by both cross-fractionation chromatography (CFC) and GPC/FT-IR. The microstructure for the resultant copolymer by 2-5 was different from those prepared by a linked type catalyst (6) and was fairly dependent upon the cyclopentadienyl fragment used.