Nucleophilic catalysis of halide displacement from brominated poly(isobutylene-co-isoprene)

The dynamics of halide displacement from brominated poly(isobutylene-co-isoprene)(BIIR) by carboxylate nucleophiles are detailed and discussed in terms of a general reaction mechanism. The exomethylene allylic bromide isomer within BIIR is shown to undergo simultaneous SN2 alkylation of Bu4Nacetate and SN2′ rearrangement with Bu4NBr. The latter generates a Z-BrMe isomer that is more reactive toward esterification. Hence, overall polymer modification rates are auto-accelerating, as Bu4NBr liberated by esterification catalyzes allylic bromide rearrangement to a more reactive electrophile. This knowledge of reaction mechanisms is used to develop nucleophilic catalysis techniques involving iodide intermediates.