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Isobutene Polymerization and Copolymerization with Isoprene Initiated by [Cp*TiMe2]+ in the Presence of a Novel Type of Weakly Coordinating Counteranion

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Abstract

Summary: The highly electrophilic borane B(C6F5)3 reacts with octadecanoic acid (n-C17H35CO2H, stearic acid) to form 1:1 and 2:1 adducts [n-C17H35CO2H][B(C6F5)3] and [n-C17H35CO2H][B(C6F5)3]2. These adducts exhibit enhanced acidities, and react with Cp*TiMe3 in methylene chloride and toluene to give methane and the complexes [Cp*TiMe2][n-C17H35CO2{B(C6F5)3}1,2]; the 2:1 complex in particular is a very good initiator for the carbocationic polymerization of isobutene (IB) and copolymerization of IB with isoprene at temperatures as high as −30 °C. High conversions to high molecular weight homo- and copolymers are obtained, consistent with the anion [n-C17H35CO2{B(C6F5)3}2] being very weakly coordinating.

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Novel class of Brønsted acidic initiators behave as very good initiators, e.g. in homopolymerisation of isobutene.

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