Exxon Bromobutyl 2233 Brominated copolymer of isobutylene and isoprene ExxonMobil Chemical Rubber - Elastomer >> Butyl rubber, IIR SEALANT ADHESIVE Bromobutyl rubber. Brominated copolymer of isobutylene and isoprene. Bromobutyl rubber. Brominated copolymer of isobutylene and isoprene.