Synthetic rubber

Synthetic rubber is any type of artificially made polymer material which acts as an elastomer. An elastomer is a material with the mechanical (or material) property that it can undergo much more elastic deformation under stress than most materials and still return to its previous size without permanent deformation. Synthetic rubber serves as a substitute for natural rubber in many cases, especially when improved material properties are needed.

Natural rubber coming from latex is mostly polymerized isoprene with a small percentage of impurities in it. This will limit the range of properties available to it. Also, there are limitations on the proportions of cis and trans double bonds resulting from methods of polymerizing natural latex. This also limits the range of properties available to natural rubber, although addition of sulfur and vulcanization are used to improve the properties.

However, synthetic rubber can be made from the polymerization of a variety of monomers including isoprene (2-methyl-1,3-butadiene), 1,3-butadiene, chloroprene (2-chloro-1,3-butadiene), and isobutylene (methylpropene) with a small percentage of isoprene for cross-linking. Furthermore, these and other monomers can be mixed in various desirable proportions to be copolymerized for a wide range of physical, mechanical, and chemical properties. The monomers can be produced pure and addition of impurities or additives can be controlled by design to give optimal properties. Polymerization of pure monomers can be better controlled to give a desired proportion of cis and trans double bonds.

History
The expanded use of motor vehicles, and particularly motor vehicle tires, starting in the 1890s, created increased demand for rubber. Political problems that resulted from great fluctuations in the cost of natural rubber led to enactment of the Stevenson Act in 1921. This act essentially created a cartel which supported rubber prices by regulating production (see OPEC), but insufficient supply, especially due to wartime shortages, also led to a search for alternative forms of synthetic rubber.

In 1879, Bouchardt created one form of synthetic rubber, producing a polymer of isoprene in a laboratory. Scientists in England and Germany developed alternate methods for creating isoprene polymers from 1910-1912.

The first large-scale commercial production occurred in Germany during World War I, as a result of shortages of natural rubber. However, it used a different form of synthetic rubber based on a polymer of butadiene, building on the laboratory work of the Russian scientist Sergei Lebedev. This early form of synthetic rubber was again replaced with natural rubber after the war ended, but investigations of synthetic rubber continued, leading to the 1933 invention which German scientists designated "Buna S". This type of synthetic rubber, a copolymer of butadiene and styrene, still represents about one-half of total world production. Dr. Waldo Semon of the B.F. Goodrich Company developed Koroseal in 1935, and Ameripol (from AMERican POLymer) in 1940, while Russian researchers created Sovprene. By 1925 the price of natural rubber had increased to the point that many companies were exploring methods of producing synthetic rubber to compete with natural rubber. In the United States, the investigation focused on different materials than in Europe. Building on the early laboratory work of Nieuwland, the DuPont company began the commercial sale of Neoprene in 1931, and Thiokol began the sale of that brand of rubber, based on ethylene dichloride in 1930. The production of synthetic rubber in the United States expanded greatly during World War II, since the Axis Powers controlled nearly all the world's supply of natural rubber once Japan conquered Asia. Additional refinements to the process of creating synthetic rubber continued after the war, and the quantity of synthetic rubber exceeded the production of natural rubber by the early 1960s.