Isoprene

The majority of isoprene produced commercially is used to make synthetic rubber (cis-polyisoprene), most of which is used to produce vehicle tires. The second- and third-largest uses are in the production of styrene-isoprene-styrene block polymers and butyl rubber (isobutene-isoprene copolymer) (IARC 1994).
Isoprene is the monomeric unit of polyisoprene. The structure of this molecule is very similar to that of butadiene, with a simple methyl substitution differentiating the two. Although it is mainly used in the production of polyisoprene, isoprene is also used in styrene-based polymers and in butyl rubber. At room temperature it is a clear, colorless liquid with a faint odor; it is insoluble in water but soluble in acetone and other organic solvents. Unlike the chemically similar butadiene, isoprene is found in abundance in nature; for example, it is a component of natural terpenes and also is expired by plants and humans.