The invention: The first commercially practical synthetic rubber, Neoprene gave a boost to polymer chemistry and the search for new materials. The people behind the invention: Wallace Hume Carothers (1896-1937), an American chemist Arnold Miller Collins (1899- ), an American chemist Elmer Keiser Bolton (1886-1968), an American chemist Julius Arthur Nieuwland (1879-1936), a Belgian American priest, botanist, and chemist Synthetic Rubber: A Mirage? The growing dependence of the industrialized nations upon elastomers (elastic substances) and the shortcomings of natural rubber motivated the twentieth century quest for rubber substitutes. By 1914
, rubber had become nearly as indispensable as coal or iron. The rise of the automobile industry, in particular, had created a strong demand for rubber. Unfortunately, the availability of rubber was limited by periodic shortages and spiraling prices. Furthermore, the particular properties of natural rubber, such as its lack of resistance to oxygen, oils, and extreme temperatures, restrict its usefulness in certain applications. These limitations stimulated a search for special-purpose rubber substitutes. Interest in synthetic rubber dates back to the 1860 discovery by the English chemist Greville Williams that the main constituent of rubber is isoprene, a liquid hydrocarbon. Nineteenth century chemists attempted unsuccessfully to transform isoprene into rubber. The first large-scale production of a rubber substitute occurred duringWorldWar I. ABritish blockade forced Germany to begin to manufacture methyl rubber in 1916, but methyl rubber turned out to be a poor substitute for natural rubber. When the war ended in 1918, a practical synthetic rubber was still only a mirage. Nevertheless, a breakthrough was on the horizon.Mirage Becomes Reality In 1930, chemists at E. I. Du Pont de Nemours discovered the elastomer known as neoprene. Of the more than twenty chemists who helped to make this discovery possible, four stand out: Elmer Bolton, Julius Nieuwland, Wallace Carothers, and Arnold Collins. Bolton directed Du Pont’s drystuffs department in the mid- 1920’s. Largely because of the rapidly increasing price of rubber, he initiated a project to synthesize an elastomer from acetylene, a gaseous hydrocarbon. In December, 1925, Bolton attended the American Chemical Society’s convention in Rochester, New York, and heard a presentation dealing with acetylene reactions. The presenter was Julius Nieuwland, the foremost authority on the chemistry of acetylene. Nieuwland was a professor of organic chemistry at the University of Notre Dame. (One of his students was the legendary football coach Knute Rockne.) The priest-scientist had been investigating acetylene reactions for more than twenty years. Using a copper chloride catalyst he had discovered, he isolated a new compound, divinylacetylene (DVA). He later treated DVA with a vulcanizing (hardening) agent and succeeded in producing a rubberlike substance, but the substance proved to be too soft for practical use. Bolton immediately recognized the importance of Nieuwland’s discoveries and discussed with him the possibility of using DVAas a raw material for a synthetic rubber. Seven months later, an alliance was formed that permitted Du Pont researchers to use Nieuwland’s copper catalyst. Bolton hoped that the catalyst would be the key to making an elastomer from acetylene. As it turned out, Nieuwland’s catalyst was indispensable for manufacturing neoprene. Over the next several years, Du Pont scientists tried unsuccessfully to produce rubberlike materials. Using Nieuwland’s catalyst, they managed to prepare DVA and also to isolate monovinylacetylene (MVA), a new compound that eventually proved to be the vital intermediate chemical in the making of neoprene. Reactions of MVA and DVA, however, produced only hard, brittle materials. In 1928, Du Pont hired a thirty-one-year-old Harvard instructor, Wallace Carothers, to direct the organic chemicals group. He began a systematic exploration of polymers (complex molecules). In early 1930, he accepted an assignment to investigate the chemistry of DVA. He appointed one of his assistants, Arnold Collins, to conduct the laboratory experiments. Carothers suggested that Collins should explore the reaction between MVA and hydrogen chloride. His suggestion would lead to the discovery of neoprene. One of Collins’s experiments yielded a new liquid, and on April 17, 1930, he recorded in his laboratory notebook that the liquid had solidified into a rubbery substance. When he dropped it on a bench, it bounced. This was the first batch of neoprene. Carothers named Collins’s liquid “chloroprene.” Chloroprene is analogous structurally to isoprene, but it polymerizes much more rapidly. Carothers conducted extensive investigations of the chemistry of chloroprene and related compounds. His studies were the foundation for Du Pont’s development of an elastomer that was superior to all previously known synthetic rubbers. Du Pont chemists, including Carothers and Collins, formally introduced neoprene—originally called “DuPrene”—on November 3, 1931, at the meeting of the American Chemical Society in Akron, Ohio. Nine months later, the new elastomer began to be sold. Impact The introduction of neoprene was a milestone in humankind’s development of new materials. It was the first synthetic rubber worthy of the name. Neoprene possessed higher tensile strength than rubber and much better resistance to abrasion, oxygen, heat, oils, and chemicals. Its main applications included jacketing for electric wires and cables, work-shoe soles, gasoline hoses, and conveyor and powertransmission belting. By 1939, when Adolf Hitler’s troops invaded Poland, nearly every major industry in America was using neoprene. After the Japanese bombing of Pearl Harbor, in 1941, the elastomer became even more valuable to the United States. It helped the United States and its allies survive the critical shortage of natural rubber that resulted when Japan seized Malayan rubber plantations. A scientifically and technologically significant side effect of the introduction of neoprene was the stimulus that the breakthrough gave to polymer research. Chemists had long debated whether polymers were mysterious aggregates of smaller units or were genuine molecules. Carothers ended the debate by demonstrating in a series of now-classic papers that polymers were indeed ordinary— but very large—molecules. In the 1930’s, he put polymer studies on a firm footing. The advance of polymer science led, in turn, to the development of additional elastomers and synthetic fibers, including nylon, which was invented by Carothers himself in 1935.