Synthesis of ethylene–norbornene–1-octene terpolymers with high 1-octene contents, molar masses, and tunable Tg values, in high yields using half-titanocene catalysts

Abstract

Terpolymerizations of ethylene (E) and norbornene (N) with 1-octene (O) using different aryloxo- or ketimide-modified half-titanocene catalysts, Cp′TiCl₂(O-2,6-ⁱPr₂C₆H₃) [Cp′ = indenyl (1), C₅Me₅ (Cp*, 2), ^tBuC₅H₄ (3)] and Cp′TiCl₂(NC^tBu₂) [Cp′ = ^tBuC₅H₄ (4), Cp (5)], in the presence of MAO cocatalysts were investigated. The microstructures, termonomer contents, and molecular weights of the resultant terpolymers, and their thermal properties were determined. The ketimide-modified Cp′TiCl₂(NC^tBu₂) (4 and 5) exhibited higher catalytic activities and yielded higher molecular weight terpolymers, poly(E-ter–N-ter–O)s, than the aryloxo-modified Cp′TiCl₂(O-2,6-ⁱPr₂C₆H₃) (1–3); the 1-octene incorporation is often higher than that prepared using ansa-metallocenes, noticeably reaching 13.5 mol%. Terpolymers prepared using ketimide-modified Cp′TiCl₂(NC^tBu₂) possessed significantly higher M_n values than the E/N copolymers; the same trend is observed in the terpolymers prepared using the Cp*-aryloxo analogue (2). This has been demonstrated to be correlated with the lower propensity of catalysts 4 and 5 to provide β-H elimination, which occurred at the last-inserted E unit, as suggested through the analysis of the vinyl end groups observed in the ¹H NMR spectra. This unique behaviour is quite different from that of well-developed ansa-metallocenes. Thus, poly(E-ter–N-ter–O)s with high O contents, molar masses, and T_g values from 23 °C to 153 °C were obtained in high yields using 2, 4, and 5 half-titanocene catalysts.