Polyisobutylene-containing block polymers by sequential monomer addition. I. The living carbocationic polymerization of styrene

The living carbocationic polymerisation of styrene (St) has been investigated by the 2-chloro-2,4,4-trimethylpentane (TMPCI)/TiCl₄ initiating system in the presence of various additives such as electron pair donors (ED_s) and the proton trap 2,6-di-tert-butylpyridine (DtBP) by the use of the mixed solvent CH₃Cl/methyl-cyclohexane (MCHx) (40/60 v/v) at ?80°C under conventional laboratory conditions. The TMPCl/TiCl₄ system in the absence of additives produces ill-defined bimodal molecular weight distribution (MWD) polymers. Much better defined polystyrenes (PSt) can be obtained in the presence of EDs, such as N,N-dimethylacetamide (DMA) and hexamethylphosphoramide (HMPA). Monomer depletion should be avoided to prevent intra- or intermolecular alkylation yielding indanyl end groups or branched polymers, respectively. In the combined presence of an ED and the proton trap, i.e., DMA + DtBP, the living polymerization of St has been achieved and thus the foundations for the carbocationic synthesis of PSt block polymers by sequential monomer addition have been laid.