Living carbocationic polymerization

A new family of initiating systems has been discovered that efficiently induces the truly living polymerization of isobutylene (IB). The initiating systems are complexes of organic tertiary esters e.g., cumyl acetate, 2,4,4-trimethylpentane-2-acetate, with BCl3. Living polymerizations proceed very rapidly in a variety of solvents, i.e., CH3Cl, CH2Cl2, C2H5Cl, and mixtures of chlorinated solvents plus n-hexane, in the range from −10° to −50°C. The living nature of the polymerizations was demonstrated by linear ¯Mn versus WPIB (g of polymer formed) plots starting at the origin and horizontal N (number of PIB chains) versus WPIB plots. The DPn of the products obeys [Mo]/[Io] where [Mo] and [Io] are initial monomer and initiator concentrations, respectively. Conversions and initiator efficiencies are ∼100%. In carefully controlled experiments narrow molecular weight distribution polyisobutylenes (PIB) have been obtained, i.e., Mw/Mn=1.17 − 1.3. A mechanism is outlined that helps rationalize the findings. It is postulated that the living polymerization of IB initiated by organic tertiary ester·BCl3 complexes most likely proceeds by a two-component group transfer polymerization process.