Polyisobutylene (PIB) is a low volume commodity thermoplastic. The lower molecular weight grades are colorless to light yellow viscous liquids or sticky solids and the high molecular weight grades are rubbery materials. Isobutylene is often copolymerized with a small amount of isoprene which provides sides for crosslinking (vulcanization). This random copolymer is called butyl rubber (IIR). It is known for its excellent impermeability, good flexibilty and good weathering properties. It also has very good stability against stress cracking, and corrosion and is weldable.
