The Synthesis of Bromobutyl Rubbers with Desired Allylic Bromide Structures and Mechanism Suggestion

Bromobutyl rubbers with desired allylic bromide structures were synthesized by solution and bulk reaction, and the microstructures of resulted products were explained. It was found that in the presence of NaOH aqueous, β-Br structure was strongly predominant (about 80%), which is in consistence with literature. In this paper, a greatly increased and a varied content of α-Br structure (66–79%) for bromobutyl rubber was obtained when the brominating reaction was carried out in an acidic environment in which NaOH aqueous was not used. When the brominating was carried out in bulk also in an acidic environment, a predominant α-Br structure (72%) was obtained again. The advanced performance could be expected due to big curing ability of α-Br structure unit in bromobutyl rubber. The brominating reactivity of both cis- and trans-isoprene units was investigated thoroughly in acidic and basic conditions. The brominated butyl rubbers with different allylic bromide structures were synthesized easily according to this study. The transformation of different microstructures was also studied and the possible mechanism was suggested.