Butyl rubber (IIR): properties, production, applications

Butyl rubber (IIR) is a synthetic rubber, a copolymer of isobutylene with a small amount (1–5% by weight) of isoprene. Thanks to its unique combination of properties — exceptionally high gas and vapour impermeability, high heat resistance, resistance to thermo-oxidative degradation and ozone ageing — butyl rubber occupies a special place among elastomers and is an indispensable material in the tyre industry, rubber technical products, construction and medicine.

History of Discovery and Development

Butyl rubber was first synthesised by a group of scientists at Exxon Research and Engineering Co. under the direction of W.J. Sparks and R.M. Thomas in 1937. In the USSR, industrial production of butyl rubber began in 1956. In 1982, a solution polymerisation technology for butyl rubber was developed and implemented in the USSR, becoming an alternative to the traditional slurry method.

Chemical Structure and Synthesis

Butyl rubber is produced by cationic copolymerisation of isobutylene and isoprene in the presence of Friedel-Crafts catalysts. Two industrial processes for butyl rubber production are known:

Slurry process — heterogeneous copolymerisation of isobutylene and isoprene is carried out in methyl chloride or ethyl chloride medium (which does not dissolve the rubber) at temperatures from –95 to –100 °C. Aluminium trichloride (AlCl₃) solution in methyl chloride is used as a catalyst. The resulting polymer dispersion in the solvent has lower viscosity, allowing higher monomer concentrations in the initial feed (22–35% by weight).

Solution process — homogeneous copolymerisation of isobutylene and isoprene is carried out in the presence of a protonated complex of halogenoaluminium organic compounds in a hydrocarbon solvent (isopentane) at temperatures from –50 to –60 °C. This technology was developed in the USSR and implemented in 1982.

Properties of Butyl Rubber

Gas and Vapour Impermeability. This is the key feature of butyl rubber: in terms of gas impermeability, it surpasses all known rubbers. The isobutylene nature of butyl rubber determines its low gas and moisture permeability. The gas permeability coefficients of butyl rubber for hydrogen, oxygen and nitrogen are 55×10⁻¹⁸, 9.9×10⁻¹⁸ and 2.47×10⁻¹⁸ m²/(s·N/m²), respectively.

Thermal and Chemical Resistance. Butyl rubber vulcanisates are characterised by high heat resistance, resistance to thermo-oxidative degradation and ozone ageing. They perform stably in aggressive environments (oxidising agents, acids, alkalis), making them suitable for lining chemical equipment. Butyl rubber is resistant to water and does not dissolve in alcohols, ethers, ketones, dichloroethane, aniline or nitrobenzene.

Physical and Mechanical Properties. The density of butyl rubber is 0.92 g/cm³. The tensile strength of the vulcanisate is approximately 11–15 MPa. Molecular weight ranges from 100,000 to 500,000. The operating temperature range is from –60 to +150 °C.

Low Unsaturation. A feature that distinguishes butyl rubber from natural and styrene-butadiene rubber is its low unsaturation, which is about 3% of the unsaturation of natural rubber.

Modification: Halobutyl Rubbers

The main route for modifying butyl rubber is its halogenation. Halobutyl rubbers (HIIR) are chemical derivatives of butyl rubber obtained by ionic halogenation of the double bonds of isoprene fragments. Halogenation is carried out in a naphtha solution and proceeds mainly by hydrogen atom substitution in the isoprene chains.

Two main types of halobutyl rubbers are produced:

• Chlorobutyl rubber (CIIR) — obtained by chlorination of butyl rubber.

• Bromobutyl rubber (BIIR) — obtained by bromination of butyl rubber.

Halogenation imparts increased vulcanisation activity to the rubber, and the vulcanisates gain increased heat resistance and adhesive strength. Bromobutyl rubber has high gas impermeability, resistance to thermal and ozone ageing, good anti-vibration properties and chemical resistance to polar solvents.

Applications

Butyl rubber and halobutyl rubbers find wide application in various industries:

Tyre Industry. The main consumer of butyl rubber. Butyl rubber is used for inner tubes and the inner liner of tubeless tyres, as well as curing bladders and diaphragms for tyre vulcanisers. Halobutyl rubbers are used for inner liners of tubeless passenger tyres.

Rubber Technical Products. Production of conveyor belts, hoses, rubberised fabrics, linings for chemical equipment. Halobutyl rubber is used for high-temperature hoses, conveyor belts, vibration mounts, dampers, shock absorbers and vibration isolators.

Construction. Butyl rubber is used for waterproofing materials, roofing membranes and sealants.

Medical and Food Industries. Special grades such as BK-1675M are intended for medical and food-grade products. Grade BK-1675P, developed specifically for the food industry, is used as a base for chewing gum production. This grade is produced by the only manufacturer in Russia — Nizhnekamskneftekhim.

Insulation and Electrical Engineering. Butyl rubber is used for insulation of metal pipes (Biakspen-NK) and high-voltage cables.

Chemical Industry. Thanks to its resistance to aggressive media, butyl rubber is used for lining chemical equipment and mining equipment.

Consumer Goods. Butyl rubber is used in the production of artificial leather, linoleum and dirt-proof mats.

Global Market

The global butyl rubber market shows steady growth. In 2025, the market was valued at USD 3.99 billion. According to other estimates, the market was USD 3.451–3.551 billion in 2024, with a projected growth to USD 4.703–4.808 billion by 2031 at a CAGR of 4.7–4.8%. The isobutylene-isoprene rubber (IIR) market was valued at USD 5.52 billion in 2025, with a projected growth to USD 7.45 billion by 2032 (CAGR 5.3%).

Key players in the global market include ExxonMobil Chemical, Lanxess, Arlanxeo, Sibur and others.

In Russia, the largest producer of butyl rubber is Sibur, which accounts for 25% of global butyl and halobutyl rubber production. Production is carried out at two sites: Nizhnekamskneftekhim (Republic of Tatarstan) and Sibur Togliatti. Nizhnekamskneftekhim is the world's largest producer of halobutyl rubber.

In the EAEU and CIS, visible consumption of butyl rubber is expected to increase by an average of 2–4% per year in 2026–2035, reaching a level 20–30% higher than 2025 figures by 2035.

Conclusion

Butyl rubber (IIR) is a unique synthetic elastomer with record gas impermeability, high heat and chemical resistance. Thanks to these properties, it is an indispensable material for tyre production, rubber technical products, waterproofing materials and medical devices. Halogenated modifications — chlorobutyl and bromobutyl rubber — significantly expand the application area of the material, providing enhanced adhesion and compatibility with other elastomers. The development of production capacities in Russia and worldwide, as well as growing demand in the automotive industry, determine the sustainable growth of the butyl rubber market in the long term.