Butyl rubber 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, having two methyl groups substituted on every other carbon atom. Polyisobutylene is a colorless to light yellow viscoelastic material. It is generally odorless and tasteless, though it may exhibit a slight characteristic odor.
Butyl rubber has excellent impermeability, and the long polyisobutylene segments of its polymer chains give it good flex properties.
The formula for PIB is: -(-CH2-C(CH3)2-)n-
The formula for IIR is:
It can be made from the monomer isobutylene or 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, 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.
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Polyisobutylene was first developed by the BASF unit of IG Farben in 1931 and sold under the trade name Oppanol B. 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 just two companies, ExxonMobil, the successor to Standard Oil, and LANXESS, a spinoff from Bayer.[1] Texas Petrochemicals (TPC Group) is the largest manufacturer of PIB in North America.
In 1950s and 1960s, halogenated butyl rubber (halobutyl) was developed, in its chlorinated (chlorobutyl) and brominated (bromobutyl) variants, providing significantly higher curing rates and allowing covulcanization with such other rubbers as natural rubber and styrene-butadiene rubber. Halobutyl is today the most important material for the inner linings of tubeless tires.
Polyisobutylene (in the form of polyisobutylene succinimide, PIBSI) has interesting properties when used as an additive in lubricating oils and motor fuels. Polyisobutylene added in small amounts to the lubricating oils used in machining results in a significant reduction in the generation of oil mist and thus reduces the operator's inhalation of oil mist.[2] It is also used to clean up waterborne oil spills as part of the commercial product Elastol. When added to crude oil it increases the oil's viscoelasticity when pulled, causing the oil to resist breakup when it is vacuumed from the surface of the water.
As a fuel additive, polyisobutylene has detergent properties. When added to diesel fuel, it resists fouling of fuel injectors, leading to reduced hydrocarbon and particulate emissions.[3] 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.[4]
Polyisobutylene is used in some formulations as a thickening agent.
Butyl rubber is used for the bladders in basketballs, footballs, soccer balls and other inflatable balls to provide a tough, airtight inner compartment.
Butyl rubber sealant is used for rubber roof repair and for maintenance of roof membranes (especially around the edges). It is important to have the roof membrane fixed, as a lot of fixtures (i.e., air conditioner vents, plumbing and other pipes, etc.) can considerably loosen it.
Rubber roofing typically refers to a specific type of roofing materials that are made of ethylene propylene diene monomers (EPDM). 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 ideal for repairing and waterproofing metal roofs.
Butyl rubber is one of the most robust elastomers when subjected to chemical warfare agents and decontamination materials. It is a harder and less porous material than other elastomers, such as natural rubber or silicone, but still has enough elasticity to form an airtight seal. While butyl rubber will break down when exposed to agents such as NH3 (ammonia) or certain solvents, it breaks down more slowly than comparable elastomers. It is therefore used to create seals in gas masks and other protective clothing.
Many varieties of chewing gum utilize food-grade butyl rubber as the central gum base.
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