Exxon Bromobutyl SB 6222 Brominated copolymer of isobutylene and isoprene ExxonMobil Chemical Rubber - Elastomer >> Butyl rubber, IIR SEALANT ADHESIVE Bromobutyl rubber. brominated copolymer of isobutylene and isoprene, including a styrene block copolymer branching agent. Bromobutyl rubber. Brominated copolymer of isobutylene and isoprene including a styrene block copolymer branching agent.