The invention: A resilient, high-strength polymer with applications ranging from women’s hose to safety nets used in space flights.
The people behind the invention:
Wallace Hume Carothers (1896-1937), an American organic chemist
Charles M. A. Stine (1882-1954), an American chemist and
director of chemical research at Du Pont Elmer Keiser Bolton (1886-1968), an American industrial chemist
In the twentieth century, American corporations created industrial research laboratories. Their directors became the organizers of inventions, and their scientists served as the sources of creativity. The research program of E. I. Du Pont de Nemours and Company (Du Pont), through its most famous invention—nylon—became the model for scientifically based industrial research in the chemical industry.
During World War I (1914-1918), Du Pont tried to diversify, concerned that after the war it would not be able to expand with only explosives as a product. Charles M. A. Stine, Du Pont’s director of chemical research, proposed that Du Pont should move into fundamental research by hiring first-rate academic scientists and giving them freedom to work on important problems in organic chemistry. He convinced company executives that a program to explore the fundamental science underlying Du Pont’s technology would ultimately result in discoveries of value to the company. In 1927, Du Pont gave him a new laboratory for research. Stine visited universities in search of brilliant, but not-yet-established, young scientists. He hired Wallace Hume Carothers. Stine suggested that Carothers do fundamental research in polymer chemistry.
Before the 1920′s, polymers were a mystery to chemists. Polymeric materials were the result of ingenious laboratory practice, and this practice ran far ahead of theory and understanding. German chemists debated whether polymers were aggregates of smaller units held together by some unknown special force or genuine molecules held together by ordinary chemical bonds.
German chemist Hermann Staudinger asserted that they were large molecules with endlessly repeating units. Carothers shared this view, and he devised a scheme to prove it by synthesizing very large molecules by simple reactions in such a way as to leave no doubt about their structure. Carothers’s synthesis of polymers revealed that they were ordinary molecules but giant in size.
The Longest Molecule
In April, 1930, Carothers’s research group produced two major innovations: neoprene synthetic rubber and the first laboratory-synthesized fiber. Neither result was the goal of their research. Neo-prene was an incidental discovery during a project to study short polymers of acetylene. During experimentation, an unexpected substance appeared that polymerized spontaneously. Carothers studied its chemistry and developed the process into the first successful synthetic rubber made in the United States.
The other discovery was an unexpected outcome of the group’s project to synthesize polyesters by the reaction of acids and alcohols. Their goal was to create a polyester that could react indefinitely to form a substance with high molecular weight. The scientists encountered a molecular weight limit of about 5,000 units to the size of the polyesters, until Carothers realized that the reaction also produced water, which was decomposing polyesters back into acid and alcohol. Carothers and his associate Julian Hill devised an apparatus to remove the water as it formed. The result was a polyester with a molecular weight of more than 12,000, far higher than any previous polymer.
Hill, while removing a sample from the apparatus, found that he could draw it out into filaments that on cooling could be stretched to form very strong fibers. This procedure, called “cold-drawing,” oriented the molecules from a random arrangement into a long, linear
one of great strength. The polyester fiber, however, was unsuitable for textiles because of its low melting point.
In June, 1930, Du Pont promoted Stine; his replacement as research director was Elmer Keiser Bolton. Bolton wanted to control fundamental research more closely, relating it to projects that would pay off and not allowing the research group freedom to pursue purely theoretical questions.
Despite their differences, Carothers and Bolton shared an interest in fiber research. On May 24, 1934, Bolton’s assistant Donald Coffman “drew” a strong fiber from a new polyamide. This was the first nylon fiber, although not the one commercialized by Du Pont. The nylon fiber was high-melting and tough, and it seemed that a practical synthetic fiber might be feasible.
By summer of 1934, the fiber project was the heart of the research group’s activity. The one that had the best fiber properties was nylon 5-10, the number referring to the number of carbon atoms in the amine and acid chains. Yet the nylon 6-6 prepared on February 28, 1935, became Du Pont’s nylon. Nylon 5-10 had some advantages, but Bolton realized that its components would be unsuitable for commercial production, whereas those of nylon 6-6 could be obtained from chemicals in coal.
A determined Bolton pursued nylon’s practical development, a process that required nearly four years. Finally, in April, 1937, Du Pont filed a patent for synthetic fibers, which included a statement by Carothers that there was no previous work on poly-amides; this was a major breakthrough. After Carothers’s death on April 29, 1937, the patent was issued posthumously and assigned to Du Pont. Du Pont made the first public announcement of nylon on October 27, 1938.
Nylon was a generic term for polyamides, and several types of nylon became commercially important in addition to nylon 6-6. These nylons found widespread use as both a fiber and a moldable plastic. Since it resisted abrasion and crushing, was nonabsorbent, was stronger than steel on a weight-for-weight basis, and was almost nonflammable, it embraced an astonishing range of uses: in
laces, screens, surgical sutures, paint, toothbrushes, violin strings, coatings for electrical wires, lingerie, evening gowns, leotards, athletic equipment, outdoor furniture, shower curtains, handbags, sails, luggage, fish nets, carpets, slip covers, bus seats, and even safety nets on the space shuttle.
The invention of nylon stimulated notable advances in the chemistry and technology of polymers. Some historians of technology have even dubbed the postwar period as the “age of plastics,” the age of synthetic products based on the chemistry of giant molecules made by ingenious chemists and engineers.
The success of nylon and other synthetics, however, has come at a cost. Several environmental problems have surfaced, such as those created by the nondegradable feature of some plastics, and there is the problem of the increasing utilization of valuable, vanishing resources, such as petroleum, which contains the essential chemicals needed to make polymers. The challenge to reuse and recycle these polymers is being addressed by both scientists and policymakers.
See also Buna rubber; Neoprene; Orlon; Plastic; Polyester; Polyethylene; Polystyrene.