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Butyl rubber, sometimes just called butyl, is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for isobutylene isoprene rubber. Polyisobutylene, also known as "PIB" or polyisobutene, (C4H8)n, is the homopolymer of isobutylene, or 2-methyl-1-propene, on which butyl rubber is based. Butyl rubber is produced by polymerization of about 98% of isobutylene with about 2% of isoprene. Structurally, polyisobutylene resembles polypropylene, but has two substituted on every other carbon atom, rather than one. 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 for PIB is: –(–CH2–C(CH3)2–)n–
The formula for IIR is:
It can be made from the monomer isobutylene (CH2=C(CH3)2) only via cationic addition polymerization.
A synthetic rubber, or elastomer, butyl rubber is impermeable to air and used in many applications requiring an airtight rubber. Polyisobutylene and butyl rubber are used in the manufacture of adhesives, agricultural chemicals, fiber optic compounds, ball bladders, , and sealants, cling film, electrical fluids, Lubricant (2 stroke 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 fuel additive, and chewing gum. The first major application of butyl rubber was Inner tube. This remains an important segment of its market even today.
It was later developed into butyl rubber in 1937, by researchers William J. Sparks and Robert M. Thomas, at Standard Oil of New Jersey's Linden, N.J., laboratory. Today, the majority of the global supply of butyl rubber is produced by two companies, ExxonMobil (one of the descendants of Standard Oil) and Polymer Corporation, a Canadian federal crown corporation established in 1942 to produce artificial rubber to substitute for overseas supply cut off by World War II. It was renamed Polysar in 1976 and the rubber component became a subsidiary, Polysar Rubber Corp. The company was privatized in 1988 with its sale to NOVA Corp which, in turn, sold Polysar Rubber in 1990 to Bayer AG of Germany. In 2005 Bayer AG spun off chemical divisions, including most of the Sarnia site, creating LANXESS AG, also of Germany.
PIB homopolymers of high molecular weight (100,000–400,000 or more) are polyolefin elastomers: tough extensible rubber-like materials over a wide temperature range; with low density (0.913–0.920), low permeability and excellent electrical properties.
In the 1950s and 1960s, butyl rubber ( halobutyl) was developed, in its chlorinated ( chlorobutyl) and brominated ( bromobutyl) variants, providing significantly higher curing rates and allowing covulcanization with other rubbers such as natural rubber and styrene-butadiene rubber. Halobutyl is today the most important material for the inner linings of tubeless tires. Francis P. Baldwin received the 1979 Charles Goodyear Medal for the many patents he held for these developments.
In the spring of 2013 two incidents of PIB contamination in the English Channel, believed to be connected, were described as the worst UK marine pollution 'for decades'. The RSPB estimated over 2,600 seabirds were killed by the chemical and hundreds more were rescued and decontaminated.
As a fuel additive, polyisobutylene has detergent properties. When added to diesel fuel, it resists fouling of , leading to reduced hydrocarbon and particulate emissions. It is blended with other detergents and additives to make a "detergent package" that is added to gasoline and diesel fuel to resist buildup of deposits and engine knock.
Polyisobutylene is used in some formulations as a thickening agent.
Rubber roofing typically refers to a specific type of roofing materials that are made of ethylene propylene diene monomers (EPDM rubber). It is crucial to the integrity of such roofs to avoid using harsh abrasive materials and petroleum-based solvents for their maintenance.
Polyester fabric laminated to butyl rubber binder provides a single-sided waterproof tape that can be used on metal, PVC, and cement joints. It is used for repairing and waterproofing metal roofs.
Recycled chewing gum has also been used as a source of recovered polyisobutylene. Amongst other products, this base rubber has been manufactured into coffee cups and 'Gumdrop' gum-collecting bins. When filled, the collecting bins and their contents are shredded together and recycled again.
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