Commercial production is by copolymerization of isobutylene with isoprene.
Halogenated butyl rubber, which accounts for more than half of global consumption, is made by reacting butyl rubber in a hexane solution with either bromine or chlorine. Bayer and Exxon account for nearly 80 percent of the global capacity for butyl and halobutyl rubbers. In addition to its Sarnia plant, Bayer has 115,000 tons of capacity at Zwijndrecht, Belgium, and a joint venture with AO Nizhenkamsk in Tatarstan that produces 50,000 tons. Japan Butyl Company, a 50-50 joint venture between Exxon and Japan Synthetic Rubber Company, has capacities of 80,000 tons of butyl rubber at Kawasaki and 25,000 tons of halobutyl rubber at Kashima, both in Japan. In Baytown, Exxon has another 50,000 tons of mothballed capacity.