AbstractThe polymerization of isobutylene with BF3, BCl3, and BBr3coinitiators has been investigated. The polymerization with BCl3requires the presence of a cationogen, e.g., H2O. The presence of a polar solvent is also necessary. Surprisingly, large quantities of polar solvent are required for effective polymerization. To obtain high conversions, the mixing sequence of the reagents is critical: BCI3must be added last to charges containing the monomer and H2O in a polar solvent. Ultimate conversions increase by decreasing the temperature. Kinetic termination exists. Experiments with BF3and BBr3revealed that polymerizations induced with BF3proceed in nonpolar and/or polar media. Polymerization stops with BF3at less than complete conversion (termination exists). In contrast to findings with BCl3, polymer yields with BF3increase with increasing temperatures. BBr3is a very inefficient coinitiator, even in the presence of polar solvent, over the −10 to −90°C temperature range. A hypothesis which explains these observations has been devel