Retraction of the claim of ring expansion polymerization of isobutylene

Some three years ago in a preliminary report from this laboratory we have proposed that the polymerization of isobutylene (IB) by the -tolyl--valerolactone/BCl₃ initiating system in CH₃Cl or CH₂Cl₂ diluents at-30°C proceeds in a living manner by an unusual ring expansion mechanism and produces macrocyclic polyisobutylenes (PIBs) [1]. Extensive follow-up research confirmed the living nature of the polymerization, however, has failed to confirm the results of a key preliminary experiment upon which the proposition of macrocyclic polymer structure was based. Thus the results of a comparative hydrolysis/GPC experiment carried out with a relatively low molecular weight (Mn=5,400) PIB at -30°C under a blanket of N₂ which gave a lower apparent molecular weight after hydrolysis than the original sample before hhydrolysis, could not be confirmed with higher molecular weight samples, i.e., with Mn=12,000, 17,000 and 30,000. As a consequence we wish to retract our earlier claim in regard to the synthesis of macrocyclic PIBs by certain lactone/BCl₃ initiating systems but maintain that these polymerizations proceed in a living manner and yield asymmetric telechelic PIBs, e.g.,-chloro--carboxyl-PIBs [2].