Living carbocationic polymerization of isobutylene by tert-amyl alcohol/BCl3/1-methyl-2-pyrrolidinone initiating system

1-Methyl-2-pyrrolidinone has been investigated, for the first time, as an efficient electron-pair donor in conjunction with tert-amyl alcohol and BCl3 in CH2Cl2 diluent at -40°C for the living polymerization of isobutylene. The use of this new monofunctional initiator-transfer (minifer) system has led to the synthesis of low molecular weight, living (near-monodisperse) polyisobutylenes carrying ″ethyl″ head group and ″tert-chloro″ end group (asymmetric telechelic polyisobutylenes). The nature of these groups was confirmed by 1H-NMR spectroscopy. The living nature of the α-ethyl-ω-(tert-chloro)polyisobutylenes has been demonstrated by a linear plot, passing through the origin, of number-average molecular weight (M¯n) vs. the amount of polymer formed (Wp) and a horizontal N (number of polyisobutylene molecules) vs. Wp plot. These results are further substantiated by gel permeation chromatography data of these polymers, and the molecular weight distributions of these polymers are narrow (low M¯w/M¯n = 1.1-1.2). The initiating efficiencies (Ieff) are close to 100% with this system. Dehydrochlorination of the prepolymer has yielded an isopropylidene (exo-olefin) end group. Structure of the end group in the resulting polymer, α-ethyl-ω-(isopropenyl)polyisobutylene, was confirmed by FTIR spectroscopy.