Isobutene homo- and isobutene-isoprene copolymerization initiated by protic initiators associated with a series of novel, weakly coordinating counteranions

The highly electrophilic borane B(C6F5)3 reacts with a variety of carboxylic acids RCO2H to form 1:1 and 1:2 adducts [RCO2H][B(C6F5)3] and [RCO2H][B(C6F5)3]2. These adducts exhibit enhanced acidities, and the 1:2 adduct of n-decanoic (stearic) acid in particular is an excellent initiator for the carbocationic polymerization of isobutene and copolymerization of isobutene with isoprene in methylene chloride and methyl chloride. High conversions to high molecular weight polyisobutene and isobutene-isoprene copolymers are obtained at unusually high temperatures, consistent with the anion [n-C17H35CO2{BC6F5)3}2]− being very weakly coordinating. Interestingly, the system also exhibits a surprising, as yet not understood, dependence of polymer molecular weights on the nature of R in methyl chloride.