Synthetic rubber

Dozens of types of synthetic rubbers have been manufactured since the late 1920s. Worldwide production of industrial rubbers exceeded 30 million metric tons in the mid-2020s, and synthetic rubbers accounted for about 60 percent of that total.

Definition

Rubbers, more properly called “elastomers,” are composed of extremely long-chain molecules (in natural rubber, the molecules contain about twenty thousand repeating five-carbon units) that are bonded to each other so they cannot flow. The molecules assume a coiled shape until they are stretched; then they straighten out. The tendency to reassume the coiled form accounts for the elasticity of these materials—that is, their resumption of their original shape when stress is removed. Natural rubber is made up of units of isoprene. The residual double bonds make it possible to “vulcanize” the natural elastomer—to heat it with 1 to 3 percent sulfur to form -S-S- “cross-links” that hold adjacent molecules together so that they cannot slip and flow away. The double bonds also make the rubber vulnerable to deterioration by reaction with atmospheric oxygen and ozone. Resources used to create synthetic rubber include petroleum feedstocks, alcohol from grain, carbon black from petroleum or natural gas, finely divided silica, sulfur, and various organic and inorganic chemicals as curing agents and accelerators.

Overview

One of the earliest successful synthetic elastomers was neoprene (ASTM code CR), made of chloroprene, which resembles isoprene in molecular shape. Neoprene proved to be resistant to solvents such as gasoline and oils, unlike natural rubber, but it was expensive. It found applications in specialty tubing, electrical insulation, gaskets and seals, and protective clothing.

Both the Germans and the Russians used 1,3-butadiene (CH₂=CHCH=CH₂) in the 1930s for synthetic rubber, but the product was inferior until about 25 percent styrene (C₆H₅CH=CH₂) was included in the reaction mixture. This produced styrene-butadiene rubber (SBR), which is the most common type of synthetic elastomer in use today. In slightly varying formulations, and always with about one-third carbon black (sometimes powdered silica) as a filler and strengthener, SBR accounts for most of the modern tire rubber, which means about 75 percent of all rubber produced.

A reaction of butadiene with acrylonitrile (CH₂=CH-CN) rather than with styrene produces acrylonitrile-butadiene rubber (NBR), which has extreme solvent resistance and is used in oil hoses, oil well parts, fuel tank liners, gaskets, shoe soles, printing rolls, and even as a binder in rocket propellants. A hydrogenated form of NBR, with the residual double bonds eliminated by reaction with hydrogen, is highly resistant to air oxidation and forms films that prevent passage of gases.

The poor quality of butadiene rubber (BR) was overcome in the 1960s by the discovery of special catalysts for the rubber-producing reaction that made the geometry uniform about the double bond. This produced BR with high resistance to abrasion and cracking and with low heat buildup with flexing, qualities that have been useful in tire treads, particularly in the giant tires used on construction equipment.

Many specialty elastomers, such as ethylene-propylene copolymer (EPM), silicone rubber (MQ), fluorocarbon elastomers (FPM), epichlorohydrin elastomers (CO or ECO), and polyurethanes (PU), are produced for their special physical or chemical (resistant) properties. Synthetic elastomers generally have more stable pricing than natural alternatives, but synthetic product prices can also fluctuate due to volatile raw material costs. The automotive sector is the primary consumer of synthetic rubber, but many other industries also use it, including construction, footwear, healthcare, and adhesives.

Bibliography

"Evolution of Synthetic Rubber: Bio-Based Raw Materials and New Types of Rubber." Renewable Carbon News, 17 Apr. 2024, renewable-carbon.eu/news/evolution-of-synthetic-rubber-bio-based-raw-materials-and-new-types-of-rubber. Accessed 22 Nov. 2025.

Helwig, Brady, and Ben Noon. "The U.S. Synthetic Rubber Program: An Industrial Policy Triumph during World War II ." American Affairs, 2025, americanaffairsjournal.org/2025/02/the-u-s-synthetic-rubber-program-an-industrial-policy-triumph-during-world-war-ii. Accessed 22 Nov. 2025.

"How Is Synthetic Rubber Made?" Polymer Trade Manufacturing, Nov. 2024, epdm.co.uk/2024/11/05/how-is-synthetic-rubber-made. Accessed 22 Nov. 2025.

"Synthetic Rubber Project." Library of Congress, 10 Oct. 2024, guides.loc.gov/technical-reports/rubber. Accessed 22 Nov. 2025.

"What Is Synthetic Rubber?" ACE Laboratories, 21 Oct. 2022, www.ace-laboratories.com/what-is-synthetic-rubber. Accessed 22 Nov. 2025.