Isoprene rubber (IR): properties and applications / Articles

Isoprene rubber (IR), known in Russia as SKI (Sinteticheskiy Kauchuk Izoprenoviy), is a synthetic polymer produced by the polymerisation of isoprene. By its chemical structure and property profile, it is the closest analogue of natural rubber (NR). IR belongs to the group of general-purpose rubbers and is an ideal choice for applications where natural rubber is traditionally used, especially where high processability and stability of physical and mechanical properties are important. Unlike natural rubber, isoprene rubbers have no unpleasant odour, are biologically inert and are characterised by good water resistance.

Chemical Structure and Classification

Isoprene rubbers are cis-1,4-polyisoprene — a product of isoprene (2-methyl-1,3-butadiene) polymerisation. In terms of structure, they are as close as possible to natural rubber, which is also cis-1,4-polyisoprene. The content of cis-1,4 units in synthetic polyisoprene is at least 96%.

In Russia, the following marking of isoprene rubbers is adopted:

SKI-3 — basic cis-isoprene rubber produced by solution polymerisation in the presence of a titanium catalyst, contains a darkening antioxidant. Produced according to GOST 14925-79.
SKI-3S — light-coloured cis-isoprene rubber filled with a non-staining stabiliser. Supplied according to TU 2294-013-73776139-2009.
SKI-5 — neodymium polyisoprene with a cis-1,4 content of at least 98%, distinguished by higher stereoregularity.
SKI-5D — dielectric cis-isoprene rubber for cable products and electrically insulating rubber technical products.
SKI-5PM — a grade for food and medical rubber products.
SKI-3 ECO — "green" rubber produced from recycled tyres, with characteristics fully identical to classic isoprene rubber.

Physical and Mechanical Properties

Isoprene rubbers possess a unique set of physical and mechanical properties:

High elasticity and strength. Polyisoprene is characterised by high tensile strength, excellent elasticity and good tack. Tensile strength for SKI-3 is at least 30.4 MPa (310 kgf/cm²) at 23 °C. Elongation at break reaches 800%.

Good processing properties. Isoprene rubbers have good processability, formability and ease of vulcanisation.

Low heat build-up. Polyisoprene is characterised by low heat accumulation under dynamic loads.

Low-temperature flexibility. SKI rubbers retain elasticity at low temperatures.

Chemical resistance. The oxidation resistance, hysteresis and chemical resistance of elastomeric materials based on SKI are close to those of natural rubber.

Mooney viscosity. For SKI-3, the Mooney viscosity ML 1+4 at 100 °C is 76–85 for group I and 67–76 for group II. For SKI-3S — 72–84 (group I, top grade). Plasticity is 0.36–0.41.

Metal content. Mass fraction of iron is not more than 0.005%, titanium — not more than 0.06%. Ash content is not more than 0.6%.

Advantages over Natural Rubber

No unpleasant odour
Biological inertness and hypoallergenicity
Good water resistance
Stability of physical and mechanical properties
Absence of proteins and nitrosamines present in natural latex

Production

The production of isoprene rubbers involves several stages. The feedstock is isobutane, which is dehydrogenated to form isobutylene-containing material; isobutylene is then converted to isoprene. In the final stage, isoprene is polymerised, during which isoprene molecules join into long chains, forming the rubber polymer.

In Russia, the largest producer of isoprene rubbers is Togliattikauchuk LLC (part of the Tatneft Group), with a production capacity of 100,000 tonnes per year for synthetic isoprene rubbers. The enterprise has been operating since 1961 and supplies a quarter of the entire Russian synthetic rubber market. Togliattikauchuk's products are annually included in the "100 Best Products of Russia" list.

Another major producer is Nizhnekamskneftekhim PJSC, where modern catalysts for isoprene rubber production have been implemented.

In 2025–2026, Togliattikauchuk launched the production of innovative "green" rubber SKI-3 ECO from recycled automotive tyres. The initiative covers the full cycle: from old tyre recycling to finished rubber production. In terms of physical and mechanical characteristics, SKI-3 ECO is fully identical to classic isoprene rubber, allowing its use in the tyre industry without changing formulations or technologies.

Applications

Isoprene rubbers find wide application in various industries:

Tyre industry. The main consumer of isoprene rubbers is the production of automotive, bicycle and motorcycle tyres, as well as for sidewall lining. Polyisoprene is used in high-performance tyres.

Rubber technical products. Production of hoses, conveyor belts, drive belts, cable insulation, as well as hoses, seals, gaskets, shock absorbers and other technical products.

Medical products. Due to biological inertness and the absence of natural rubber proteins, IR is used for surgical gloves, catheters, syringes, baby bottle teats, medical tubes and other medical devices.

Footwear industry. Production of soles, shoe parts and footwear elements.

Consumer goods. Manufacture of sports equipment, children's toys, rubber mats, elastic cords, rubber bands and other consumer products.

Adhesives and sealants. Isoprene rubbers are used in adhesive compositions and bituminous mastics.

Global Market and Trends

The global polyisoprene rubber market shows steady growth. The main drivers are the expansion of automotive production, growing demand for high-performance tyres and the development of medical technologies.

Key trends include:

Development of specialised grades for medical applications
Development of sustainable production methods, including bio-based and recycled polyisoprene
Creation of environmentally friendly "green" rubbers from recycled feedstock
Improvement of catalysts to increase stereoregularity and improve properties

Conclusion

Isoprene rubbers (IR) represent a unique class of synthetic polymers that are the closest analogue of natural rubber. Thanks to high elasticity, strength, biological inertness and property stability, they find wide application in the tyre industry, rubber technical products, medical products and consumer goods. The development of "green" rubber production technologies and the improvement of catalytic systems open new prospects for this critically important material.