- Also called:
- isobutylene-isoprene rubber
- Related Topics:
- synthetic rubber
butyl rubber
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What is butyl rubber?
Butyl rubber (IIR) is a synthetic rubber created by copolymerizing isobutylene with a small amount of isoprene. It is valued for its impermeability to gases, chemical inertness, and resistance to weathering, and is used in specialty applications and the inner linings of automobile tires.
Butyl rubber is made by diluting isobutylene, cooled to approximately -100 °C, with methyl chloride, and adding low concentrations (1.5 to 4.5 percent) of isoprene in the presence of aluminum chloride. It was first produced in 1937 by William Sparks and Robert Thomas at the Standard Oil Company of New Jersey.
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What chemicals are used to make butyl rubber?
Butyl rubber (IIR) is a synthetic rubber created by copolymerizing isobutylene with a small amount of isoprene.
Both isobutylene ((C(CH_3)_2=CH_2)) and isoprene ((CH_2=C(CH_3)-CH=CH_2)) are typically sourced through thermal cracking of natural gas or lighter crude oil fractions. To process IIR, isobutylene is refrigerated to approximately -100 °C (-150 °F) and then diluted with methyl chloride. A low concentration (1.5 to 4.5 percent) of isoprene is added with aluminum chloride, which initiates a reaction where the two compounds copolymerize.
The resulting copolymer can be recovered from the solvent as a crumb, which can then be mixed with fillers and other modifiers and vulcanized to create practical rubber products.
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How is butyl rubber different from natural rubber?
Butyl rubber and natural rubber differ significantly in their composition, properties, and uses. Butyl rubber is a synthetic rubber formed by copolymerizing isobutylene with a small amount of isoprene, while natural rubber consists almost exclusively of the cis-1,4 polymer of polyisoprene obtained from the latex of certain plants like Hevea brasiliensis.
Butyl rubber is valued for its chemical inertness and impermeability to gases, making it suitable for tire linings and other specialty applications. Natural rubber is known for its extensibility and toughness, with the ability to stretch to seven or eight times its original length.
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What makes butyl rubber good for keeping air and moisture out?
Butyl rubber's impermeability to gases and resistance to oxidation makes it ideal for keeping air and moisture out.
Here's why:
* Low molecular motion Butyl rubber has a low rate of molecular motion, even above the glass transition temperature. This results in low permeability to gases.
* Few unsaturated groups With few unsaturated groups, butyl rubber resists oxidation, preventing degradation from atmospheric oxygen.
* Stereoregularity The base polymer, polyisobutylene, is stereoregular, meaning its pendant groups are arranged in a regular order along the polymer chains. This allows the chains to crystallize rapidly when stretched, providing strength.2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are some common uses for butyl rubber?
Butyl rubber, a copolymer of isobutylene with a small amount of isoprene, stands out for its chemical inertness and impermeability to gases. Because of its excellent air retention, butyl rubber is the preferred material for inner tubes and the inner liners of tubeless tires. It is also used in other automobile components such as window strips because of its oxidation resistance. Furthermore, its heat resistance makes it indispensable in tire manufacturing, where it forms bladders that retain the steam or hot water used to vulcanize tires.
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How does the structure of butyl rubber affect its properties and uses?
Butyl rubber (IIR), a synthetic rubber created by combining isobutylene with a small amount of isoprene, is valued for its impermeability to gases, chemical inertness, and resistance to weathering.
IIR's polyisobutylene base polymer is stereoregular, meaning its pendant groups are arranged in a regular order along the polymer chains. Because the chains of IIR can quickly crystallize when stretched, IIR containing only a small amount of isoprene is as strong as natural rubber. IIR also displays a low rate of molecular motion even above the glass transition temperature and is resistant to oxidation because the copolymer has few unsaturated groups.
IIR is the preferred material for inner tubes and the inner liners of tubeless tires due to its excellent air retention. It is also used for automobile components like window strips because of its oxidation resistance. In tire manufacturing, butyl rubber makes indispensable bladders that retain the hot water or steam used to vulcanize tires because of its heat resistance.
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butyl rubber (IIR), a synthetic rubber produced by copolymerizing isobutylene with small amounts of isoprene. Valued for its chemical inertness, impermeability to gases, and weatherability, butyl rubber is employed in the inner linings of automobile tires and in other specialty applications.
Both isobutylene (C[CH3]2=CH2) and isoprene (CH2=C[CH3]-CH=CH2) are usually obtained by the thermal cracking of natural gas or of the lighter fractions of crude oil. At normal temperature and pressure isobutylene is a gas and isoprene is a volatile liquid. For processing into IIR, isobutylene, refrigerated to very low temperatures (approximately −100 °C [−150 °F]), is diluted with methyl chloride. Low concentrations (1.5 to 4.5 percent) of isoprene are added in the presence of aluminum chloride, which initiates the reaction in which the two compounds copolymerize (i.e., their single-unit molecules link together to form giant, multiple-unit molecules). The polymer repeating units have the following structures: ![Industrial Polymers. The major polymers. Carbon-Chain Polymers. Vinyl copolymers. [structure of the repeating units of isobutylene and isoprene]](https://cdn.britannica.com/46/15446-004-0F6145A1/Industrial-Polymers-polymers-Vinyl-copolymers-structure-Carbon-Chain.jpg)
Because the base polymer, polyisobutylene, is stereoregular (i.e., its pendant groups are arranged in a regular order along the polymer chains) and because the chains crystallize rapidly on stretching, IIR containing only a small amount of isoprene is as strong as natural rubber. In addition, because the copolymer contains few unsaturated groups (represented by the carbon-carbon double bond located in each isoprene repeating unit), IIR is relatively resistant to oxidation—a process by which oxygen in the atmosphere reacts with the double bonds and breaks the polymer chains, thereby degrading the material. Butyl rubber also shows an unusually low rate of molecular motion well above the glass transition temperature (the temperature above which the molecules are no longer frozen in a rigid, glassy state). This lack of motion is reflected in the copolymer’s unusually low permeability to gases as well as in its outstanding resistance to attack by ozone.
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The copolymer is recovered from the solvent as a crumb, which can be compounded with fillers and other modifiers and then vulcanized into practical rubber products. Owing to its excellent air retention, butyl rubber is the preferred material for inner tubes in all but the largest sizes. It also plays an important part in the inner liners of tubeless tires. (Because of poor tread durability, all-butyl tires have not proved successful.) IIR is also used for many other automobile components, including window strips, because of its resistance to oxidation. Its resistance to heat has made it indispensable in tire manufacture, where it forms the bladders that retain the steam or hot water used to vulcanize tires.
Bromine or chlorine can be added to the small isoprene fraction of IIR to make BIIR or CIIR (known as halobutyls). The properties of these polymers are similar to those of IIR, but they can be cured more rapidly and with different and smaller amounts of curative agents. As a result, BIIR and CIIR can be cocured more readily in contact with other elastomers making up a rubber product.
Butyl rubber was first produced by American chemists William Sparks and Robert Thomas at the Standard Oil Company of New Jersey (now Exxon Corporation) in 1937. Earlier attempts to produce synthetic rubbers had involved the polymerization of dienes (hydrocarbon molecules containing two carbon-carbon double bonds) such as isoprene and butadiene. Sparks and Thomas defied convention by copolymerizing isobutylene, an olefin (hydrocarbon molecules containing only one carbon-carbon double bond) with small amounts—e.g., less than 2 percent—of isoprene. As a diene, isoprene provided the extra double bond required to cross-link the otherwise inert polymer chains, which were essentially polyisobutylene. Before experimental difficulties were resolved, butyl rubber was called “futile butyl,” but with improvements it enjoyed wide acceptance for its low permeability to gases and its excellent resistance to oxygen and ozone at normal temperatures. During World War II the copolymer was called GR-I, for Government Rubber-Isobutylene.