Polyisobutene (polyisobutylene) is a class of organic polymers prepared by polymerization of isobutene. The polymers often have the formula Me<sub>3</sub>C[CH<sub>2</sub>CMe<sub>2</sub>]<sub>n</sub>H (Me = CH<sub>3</sub>). They are typically colorless gummy solids.
Cationic polymerization, initiated with a strong Brønsted or Lewis acid, is the typical method for its production. The molecular weight (MW) of the resulting polymer determines the applications. Low MW polyisobutene, a mixture of oligomers with M<sub>n</sub>s of about 500, is used as plasticizers. Medium and high MW polyisobutenes, with M<sub>n</sub> âÂÂ¥ 20,000, are components of commercial adhesives.