Living carbocationic polymerization of isobutylene with BCl₃ coinitiation in the presence of di-tert-butylpyridine as proton trap

Summary

The living polymerization of isobutylene (IB) has been achieved with the 2,4,4-trimethylpentyl chloride (TMPCl) or cumyl chloride (CumCl)/BCl₃/(IB)/methyl chloride/-40°C system in the presence of proton trap 2,6-di-tert-butylpyridine (DTBP) in concentrations comparable to that of protic impurities. According to kinetic studies the polymerization is first order both in respect to monomer and BCl₃. The polymerization rate is not effected by the excess DTBP which suggests that the livingness is not due to carbocation stabilization. Comparison of the results in the presence of DTBP and/or dimethyl sulfoxide (DMSO) demonstrated that the main function of the electron donor (ED) DMSO is to trap protic impurities. The assumption of carbocation stabilization is unnecessary, and reversible termination and the absence of chain transfer is sufficient to explain livingness. In the absence of proton trap or ED however, fast polymerization by the protic impurities occurs masking the much slower living polymerization and the monomer is consumed mainly by this process unless the protic impurities are scavenged.