H 710 CREATIVE CHEMISTRY need not be extensible. Natural rubber suffers from several disadvantages. It swells on contact with organic liquids such as petroleum products (gasoline, lubricating oils, etc.) ; it is not resistant to oxidation by the oxygen of the air. The original synthetic rubber, a polymer of dimethylbutadiene, developed by Germany during World War I, was a poor substitute for natural rubber, but it has been greatly improved by building large molecules from a mixture of butadiene and other unsaturated compounds. Thus Buna S tires on which the German mechanized army rode in 1940-1941 were made by polymerizing butadiene with styrene. H Fig. 304. The Firestone B-iy bomber tire. (Courtesy of the Firestone Tire and Rubber Company.) I C // \ HC C—CH=CH2 HC C— \ / C I H This rubber is approximately equal to natural rubber in its resistance to abrasion and heat. Buna N, more commonly referred to as Perbunan, is another copolymer of butadiene, which is particularly desirable because of its resistance to swelling with liquid hydrocarbons. Buna N is made by polymerizing butadiene with acrylonitrile, CH2=CH—C^N. Tires made from Perbunan may wear slightly longer than tires made from natural rubber. In 1940 the Standard Oil Company, a corporation of New Jersey, made public its plans to erect a Buna plant having a capacity of 10,000 pounds per day under the patent rights originating with German chemists and now owned by one of Standard's United States subsidiaries. This plant went into operation in 1941 at the refinery of the Standard Oil Company of Louisiana in Baton Rouge.
NATURAL AND SYNTHETIC RUBBERS 711 In 1941 the United States Government arranged with four rubber companies to build synthetic rubber plants each with an initial capacity of 2500 tons per year, to be increased eventually to 10,000 tons per year for each plant. About 1930 the E. I. du Pont de Nemours Company produced a new synthetic rubber, neoprene, from the basic materials, coal, limestone, and salt. Acetylene prepared from calcium carbide was changed in the presence of catalysts (cuprous salts) to monovinyl acetylene, was HC^C—CH=CH2, which heated with hydrochloric acid, HCl, made from salt to produce CL chloroprene, HaC^-C—CH=CH2. Chloroprene is polymerized to Neoprene is produce neoprene. superior to natural rubber in its resistance to hydrocarbon solvents, to light, and to oxidation. Unlike natural rubber it does not require sulfur for vulcanization. Neoprene is used to advantage in the manufacture of hose for any purpose where oil or other hydrocarbons are likely to be present, for conveyor belts, packing, printing rollers, electrical cables, ignition wire, gloves, protective clothing, motor mountings, nonslip floor wax, and many other products which are subjected to conditions that quickly deteriorate natural rubber. The Russians make a synthetic rubber known as Sovprene, which is believed by some people to be similar to neoprene. Sovprene is the name given to the Russian version of neoprene. A self-sealing rubber airplane tank. (Courtesy of the United States Rubber Company.) In late 1941 the production of neoprene had been raised to 1,500,000 pounds per month, and a new plant was being erected by the E. I. du Pont de Nemours and Company at Louisville, Kentucky, which is to have a capacity of around 20,000,000 pounds per year. Another solvent-resisting rubber substitute which was developed at about the same time that neoprene was developed is made from ethylene dichloride and sodium tetrasulfide. The ethylene is obtained from petroleum refinery gases, and the chlorine and sodium tetrasulfide come from salt and sulfur. This rubber substitute is called "Thiokol." It was discovered by J. C. Patrick in 1920 in connection with a research for a cheaper antifreeze solution. In 1938 the consumption of "Thiokol" exceeded one million pounds.