Isobutene–isoprene copolymerization initiated by [Cp∗MMe2][(n-C18H37E)B(C6F5)3] (M = Ti, Hf; E = O, S) and related compounds

The highly electrophilic borane B(C6F5)3 reacts with e.g., n-octadecanol (n-C18H37OH) and n-octadecanethiol (n-C18H37SH) to form equilibrium mixtures of the reactants and their 1:1 adducts (n-C18H37EH)B(C6F5)3 (E = O, S). The latter are acidic, and react with Cp∗MMe3 (M = Ti, Hf) in polar and non-polar solvents to give methane and the unstable complexes [Cp∗MMe2][(n-C18H37E)B(C6F5)3]. The latter are very good initiators for the copolymerization of isobutene with isoprene at relatively high temperatures, giving high conversions to high molecular weight isobutene–isoprene copolymers. The weight average molecular weights are unusually high for the temperatures used, consistent with current theories of the role of weakly coordinating anions. The effects of changing the substituents on the alcohols are also investigated.