Nylon

Chemistry: Foundations and Applications, (2004) by Charles E. Carraher

Nylon

In 1928 E. I. du Pont de Nemours & Company (Du Pont) launched one of its first basic research programs and hired Wallace Hume Carothers to run it. He was brought to Du Pont in part because his fellow researchers at Harvard University and the University of Illinois had called him the best

Figure 1.

Figure 2. An amide unit.

synthetic chemist they knew. The program he supervised was designed to investigate the composition of natural polymers such as silk, cellulose, and rubber. Many of Carothers's efforts related to condensation polymers were based on his deduction that if a monofunctional reactant reacted in a certain manner in forming a small molecule, then similar reactions that employed a comparable reactant, but with two reactive groups, would form polymers. (See Figure 1.)

The amide unit (found in polyamides) shown in Figure 2 is the same connective grouping that is found in proteins.

Although the Carothers group had worked with both polyesters and polyamides, they initially emphasized their work on the polyesters, as polyesters were more soluble and easier to work with. Julian Hill, a member of the Carothers team, noticed that he could form fibers if he separated a portion of a soft polyester material using a glass stirring rod and pulled it away from the clump. But because the polyesters had softening points that were too low for their use as textiles, the group returned to its work with the polyamides. The researchers found that fibers could also be formed from the polyamides, similar to those formed from the polyesters. The strength of these fibers approached, and in some cases surpassed, the strengths of natural fibers. This new miracle fiber (nylon) was introduced at the 1939 New York World's Fair, in an exhibit that announced the synthesis of a wonder fiber from "coal, air, and water"—an exaggeration but nevertheless eye-catching. When the nylon stockings were first offered for sale in New York City, on May 15, 1940, over four million pairs were sold in the first few hours. Nylon stocking sales took a large drop during World War II when it became publicized that nylon was needed to make parachutes.

The polyamides (nylons) were given a special naming system. Nylons made from diamines and dicarboxylic acids are designated by two numbers, the first representing the number of carbons in the diamine chain (a) and the second the number of carbons in the di carboxylic acid (b). (See Figure 3.)

The nylon developed by Carothers at Du Pont was nylon 6,6. Because of the importance of starting out with equal amounts of the two reactants, salts of the diamine and of the diacid are made and then used in the commercial synthesis of nylon 6,6. (See Figure 4.)