Living carbocationic polymerisation. XI. Copolymerisation of isobutylene with isoprene. Initial investigations

The copolymerisation of various isobutylene (IB)‐isoprene (IP) charges has been investigated by the use of the cumyl acetate‐BCl3 complex initiating system in CH3Cl or CH2Cl2 diluents at — 30°C. Conditions have been defined under which charges containing 2 0 120mol % IP lead to living copolymerizations and yield soluble (gel‐free) copolymers containing from 1 2 to 7 8 mol % 1,4‐IP units in the M̄;n = 2400−12 100 range with M̄;w/M̄;n ∼ 1 8. Conversion (rate) and M̄;n decrease with increasing IP in the charge. The reactivity ratios in this IP range are rIB = 2 4 ± 0 35 and rIP = 4 5 ± 3 0, i.e. rIBrIP = 10 8; nonetheless the copolymers are statistical because of the very low IP contents in the charge. With 20–50 mol % IP in the charge two or more contiguous IP units will be formed at the growing chain end which may lead to cyclisation. Cyclisation leads to proton elimination which ultimately results in chain transfer to monomer. A mechanism has been developed that accounts for the observations and points the way for further research.