Synthesis of highly reactive polyisobutylenes with BF3·cyclohexanol initiating system

The selective cationic polymerization of isobutylene (IB) initiated by a BF3·cyclohexanol (CL) complex was carried out from the mixed C4 fraction feed containing the 4C saturated and unsaturated hydrocarbons at −20°C. The effects of CL concentration, BF3 concentration, solvent for preparing BF3·CL complex and polymerization time on the chemical structure of end groups, number-average molecular weight (M n) and molecular weight distribution (MWD, M w/M n) of the resulting polymers were investigated. The experimental results indicate that the BF3·CL complex initiating system exhibited an extremely high selectivity toward the cationic polymerization of IB in the mixed C4 fraction feed and low molecular weight (M n = 900–3600) polyisobutylenes (PIBs) with large proportion of exo-double bond end groups were obtained. The exo-double bond content in PIB chain ends increased by increasing CL concentration or by decreasing solvent polarity in initiating system, BF3 concentration and polymerization time. The M n and MWD of the resulting PIBs were dependent on the concentrations of CL and BF3. Highly reactive PIBs with around 90 mol% of exo-double bonds were successfully synthesized by the selective polymerization of IB from the mixed C4 fraction feed, providing a potentially practical process for its simplicity and low costs.