butylrubber

Butyl rubber is a family of synthetic elastomers based on polyisobutylene with a small amount of isoprene. The base material, polyisobutylene-co-isoprene, is produced by polymerizing isobutylene and incorporating a small fraction of isoprene to introduce unsaturation for crosslinking during vulcanization. A related group, halobutyl rubber, is formed by halogenating the base polymer to yield chlorobutyl or bromobutyl rubber. Halogenation enhances cure properties and gas barrier performance.

The distinguishing feature of butyl and halobutyl rubbers is their exceptionally low permeability to gases and moisture. This makes them highly effective as barrier materials. They also exhibit good aging and weathering resistance, low gas permeability, and good electrical insulation. Their chemical resistance is favorable to water and many solvents, though they are less resistant to certain hydrocarbons and oils. The unsaturation provided by the isoprene units allows crosslinking, which gives the elastomer its elastic properties after vulcanization. Halobutyl rubbers generally offer even higher gas impermeability and improved performance in challenging environments.

Processing and curing typically involve sulfur or peroxide vulcanization. Halobutyl rubbers are valued for their ability to maintain shape and barrier properties under wide temperature ranges and in the presence of moisture. Because of these properties, butyl and halobutyl rubbers are widely used in applications requiring gas and moisture barriers, such as tire inner liners and inner tubes, seals and gaskets, pharmaceutical stoppers, and various containment and packaging components.