butyl rubber

Butyl rubber—also known as polyisobutylene and PIB (C4H8)n is a synthetic rubber, a homopolymer of 2-methyl-1-propene. Polyisobutylene is produced by polymerization of about 98% of isobutylene with about 2% of isoprene. Structurally, polyisobutylene resembles polypropylene, having two methyl groups substituted on every other carbon atom. It has excellent impermeability, and the long polyisobutylene segments of its polymer chains give it good flex properties. Polyisobutylene is a colorless to light yellow viscoelastic material. It is generally odorless and tasteless, though it may exhibit a slight characteristic odor.

The formula is: -(-CH2-C(CH3)2-)n-

It can be made from the monomer isobutylene or CH2=C(CH3)2 only via cationic addition polymerization.

A synthetic rubber, or elastomer, polyisobutylene is impermeable to air and used in many applications requiring an airtight rubber. Polyisobutylene is used in making adhesives, agricultural chemicals, fiber optic compounds, caulks and sealants, cling film, electrical fluids, lubricants (2 cycle engine oil), paper and pulp, personal care products, pigment concentrates, for rubber and polymer modification, for protecting and sealing certain equipment for use in areas where chemical weapons are present, as a gasoline/diesel fuel additive, and even in chewing gum. The first major application of butyl rubber was tire inner tubes. This remains an important segment of its market even today.

Butyl rubber was first developed by BASF in 1931 and sold under the trade name Oppanol B. It was later developed in 1937, by researchers William J. Sparks and Robert M. Thomas, at Standard Oil's (which became Exxon in 1972) Linden, N.J. laboratory. Texas Petrochemicals and Lubrizol Corporation are one of the largest manufacturers of PIB in North America.

In 1950s and 1960s, halogenated butyl rubber (halobutyl) was developed, in its chlorinated (chlorobutyl) and brominated (bromobutyl) variant, providing significantly higher curing rates and allowing covulcanization with other rubbers like natural rubber and styrene-butadiene rubber. Halobutyl is today the most important material for inner tubes. The butyl rubber is vulcanized by elemental sulfur.