Wallace Carothers stretches a piece of neoprene in his lab at the DuPont Experimental Station in Wilmington.
A polymer is a large molecule composed of many repeated sub-units. Polymers occur in nature. Plants, for instance, are composed of a polymer called cellulose. Other polymers had been synthesized in the laboratory; a hard resin dubbed Bakelite had been a big commercial success. When Carothers came to the field, the arrangement of the sub-units within polymers was not well understood. A prominent German scientist had proposed that polymers were held together in the same way as smaller molecules—by covalent bonding, in which atoms share pairs of electrons. Carothers generally agreed. But rather than working with natural polymers, he focused on creating synthetic polymers in the lab by exposing small molecules to known reactants to form long, macromolecular chains.
That got DuPont’s attention. Stine had convinced DuPont’s executive committee to fund a continuing research program. But Carothers, who had been at Harvard only a short time, turned down Stine’s offer: “I suffer from neurotic spells of diminished capacity, which might constitute a much more serious handicap there than here,” he wrote. Stine raised his salary offer. Eventually, Carothers gave in. It worked for a while. Freed from teaching, he bicycled to work at DuPont’s Experimental Station in Wilmington and set his own agenda. “Nobody asks any questions as to how I am spending my time or what my plans are,” he wrote a friend. “Apparently, it is all up to me.”
Carothers focused, of course, on polymers and from his department’s experiments emerged polychloroprene, a synthetic rubber later introduced as “neoprene.” Synthetic rubber proved invaluable during World War II, when the Axis powers controlled most sources of natural rubber. Shortly afterward, Carothers and a lab assistant made a breakthrough in their efforts to develop polymers with molecular weights greater than 6,000. Using a new technique, the assistant dipped a glass rod into a batch of polymers with weights above 12,000 and found that the fibers began to align and become stronger as they were pulled out.
“Carothers was away on business the morning his team went running down the halls between the laboratories, pulling their bright, chemical strings behind them,” according to Financial Times writer Sam Knight. But it still needed work. Bolton was now in charge. With the Depression cutting into DuPont’s revenues, he pushed Carothers—whose interests were elsewhere—to focus on developing fibers. Meanwhile, Carothers’ parents had come to live with him. He wrote a friend of suffering “at least a dozen violent storms of depression every day.”
Bolton got what he wanted. Carothers modified his equipment and identified new combinations of chemicals. By early 1935, he had a new fiber that, by weight, was six times stronger than steel. By then, however, Carothers had had the first in a series of breakdowns. He spent time away from the office and married in early 1936, then was confined for two months at a mental institution. Badly shaken in early 1937 by the sudden death of his actress sister, Carothers learned in April that his wife was pregnant. Three days later, he drove to Philadelphia. The new fiber, nylon, was introduced the following year.