Isoprene: properties, production, applications

Isoprene (2-methyl-1,3-butadiene) is the most important representative of diene hydrocarbons and one of the key monomers in the modern petrochemical industry. It is a colourless, mobile, highly volatile and flammable liquid with a characteristic odour. The chemical formula of isoprene is C₅H₈ (CH₂=C(CH₃)–CH=CH₂), with a molar mass of 68.11 g/mol. It has been known for over a century that isoprene is the fundamental building block of natural rubber macromolecules; however, it was only in the mid-20th century that scientists succeeded in synthesising rubber that is a structural analogue and substitute for natural rubber.

Physicochemical Properties

Isoprene possesses a unique set of physicochemical characteristics. Its melting point is –145.95 °C, and its boiling point is 34.067 °C. The density at 20 °C is 0.6805 g/cm³. Isoprene is practically insoluble in water but readily soluble in most organic solvents — alcohols, ether, benzene and others.

In terms of chemical properties, isoprene exhibits all the characteristic reactions of alkadienes with conjugated double bonds. It is prone to spontaneous polymerisation; therefore, inhibitors such as hydroquinone are added during storage to prevent this process. Isoprene has toxic properties; the maximum allowable concentration (MAC) in the working area is 40 mg/m³.

Production Methods

Several main technologies for isoprene production have been implemented and are used on an industrial scale:

1. Extraction from C₅ pyrolysis fractions — the simplest and most common method. The feedstock is the C₅ fraction — a by-product of ethylene pyrolysis units. In this fraction, the isoprene content is approximately 15–20%, while other reactive components (piperylene and cyclopentadiene) account for 40–55% of the total volume. The process involves extractive distillation using solvents (dimethylformamide or acetonitrile).

2. Isopentane dehydrogenation — a two-stage process of catalytic hydrogen abstraction from isopentane. The reaction is carried out at temperatures of 300–700 °C. To shift the equilibrium towards isoprene formation, a reduction in the partial pressure of hydrocarbons using inert diluents or vacuum is employed.

3. Synthesis from isobutylene and formaldehyde — carried out via 4,4-dimethyl-1,3-dioxane (DMD) or by a one-stage scheme. This method features high atom economy and produces a high-purity product. The overall production cost is approximately 30% lower than that of the C₅ fraction extraction method.

4. Biological methods — an actively developing area using sugars (e.g., glucose) as a carbon substrate through microbial fermentation. Cyanobacteria and E. coli with an introduced isoprene synthase gene are used as producers.

The raw materials for isoprene production include the C₅ hydrocarbon fraction, isopentane, as well as isobutylene with formaldehyde — depending on the technology used.

Isoprene Rubber Production

Up to 95% of all isoprene produced is used for the production of isoprene rubbers. Synthetic polyisoprene (IR) is a structural analogue of natural rubber and is close to it in terms of its property complex. Isoprene polymerisation can be carried out by an anionic mechanism or using Ziegler-Natta catalysts.

In Russia, the most well-known grades of isoprene rubber are SKI-3 and SKI-3S. There are also grades SKI-5 (neodymium polyisoprene), used in the tyre and rubber goods industry, and SKI-5PM for the production of coloured rubber products, footwear, and products for the food industry and medicine. Cis-1,4-polyisoprene is characterised by a linear macromolecular structure. The Mooney viscosity is 65–85.

Global production capacity for synthetic isoprene rubber today exceeds 1.3 million tonnes per year.

Applications

The main consumer of isoprene rubbers is the production of automotive tyres and rubber technical products for various purposes. Isoprene is also used:

• as a comonomer in the production of butyl rubber (a copolymer of isoprene with isobutylene);

• for the synthesis of styrene-isoprene-styrene (SIS) block copolymers;

• in the synthesis of isoprene-styrene thermoplastic elastomers;

• for the production of fragrances and pharmaceuticals.

Synthetic polyisoprene finds application in medical devices (surgical gloves, catheters, condoms), high-performance tyres and vibration isolation components. Thanks to its high purity, absence of natural rubber proteins and nitrosamines, IR is a hypoallergenic alternative to natural latex.

Global Market

The global isoprene market shows steady growth. In 2024, its volume was estimated at USD 3.12 billion. It is projected to grow to USD 5.18 billion by 2032 at a CAGR of 5.9%. According to other estimates, the isoprene monomer market in 2025 was about USD 2.45 billion. Global sales volume of isoprene monomer in 2025 is projected at 840,000 tonnes with an average price of USD 2,835 per tonne.

Key market players include Nizhnekamskneftekhim, Tatneft, Synthez-Kauchuk, Shell, JSR. The top 5 producers control about 45% of global capacity. Europe is the largest market with a share of about 45%, followed by Asia-Pacific (about 30%) and North America (about 20%).

In Russia, isoprene is produced by PJSC Nizhnekamskneftekhim (the largest producer, accounting for over half of total Russian output), JSC Synthez-Kauchuk (Sterlitamak) and LLC Togliattikauchuk.

The main market growth driver is the expansion of automotive production and the growing demand for high-performance tyres. Bio-based isoprene production technologies are also being actively developed — companies Braskem and Goodyear are exploring sustainable alternatives to traditional petrochemical methods.