Many important scientific discoveries have occurred because researchers pursued 'chance' or accidental events. Nowhere is this more evident than in the history of polymers and organic chemistry. Teachers interested in teaching about the process of science will want to convey something about the role of 'serendipity'. Yet it can be difficult for students to appreciate through their own lab experiences how mishaps can be transformed into successes or how 'mistakes' can lead productively to new knowledge. One strategy is to use historical case studies that can connect with easy lab demonstrations. The following familiar molecules each have a fascinating story behind them that helps convey a lesson about the nature of science and--when linked to 'hands-on' lab activities--can also enrich a student's understanding of fundamental organic chemistry:
These stories and related lab activities also offer an ideal opportunity for introducing a unit on organic chemistry into a standard chemistry course (including polymers).
The seeds of great discoveries are constantly floating around us, but they only take root in the minds well prepared to receive them. --Joseph Henry
The curriculum material here was developed as part of a project sponsored by SciMath-MN and The Bakken Library and Museum. Click to see directory of other curriculum modules using history and philosophy of science in this series.
Click here for extended LAB ACTIVITIES on dyeing and for more information on the history of dyes in Colonial and Native America.
These compounds were shelved in order to concentrate their work on a more promising series of compounds, polyesters. Polyesters possessed more desirable properties such as having more soluble products, easier to handle and simpler to work with in the laboratory. Julian Hill, working with polyester, noticed that if you gathered a small amount of this soft polymer on the end of your stirring rod and drew it out of the beaker, it produced a silky, fine fiber. One afternoon when their boss, Wallace Carothers, was not in the lab, the chemists decided to see how long a silky thread they could produce. Hill and his cohorts took a little ball on a stirring rod and ran down the hall and stretched them out into a string. The realization struck them during this horseplay that by stretching the strand of fiber they were orienting the polymer molecules and increasing the strength of the product.
The polyesters had very low melting points, too low for textile uses, so they retrieved the polyamides from the shelf and began to experiment with this need 'cold-drawing process.' They found that the strand of polyamide produced by this cold-drawing technique produced a stron g, excellent fiber. The patent for the composition of nylon was never applied for by Du Pont, rather they chose to patent the production process -- cold-drawing -- developed by unsupervised adults playing around in the lab.
In January-February 1939, this consumer product hit the US market. It is without equal in its impact before or since. Nylon stockings were exhibited at the Golden Gate International Exposition in San Francisco and were sold first to employees of the inventor company Du Pont de Nemours. On May 15, 1940, nylon stockings went on sale throughout the US, and in New York City alone four million pairs were sold in a matter of hours.
Naming this new polymer too many twists and turns. Initially the name norun was proposed for this new product because it was more resistant to laddering than silk. But there were problems and the name was then reversed to read nuron. However, it was pointed out that this was too close to the word neuron which may be construed to be a nerve tonic. Hence, nuron was changed nulon. However this ran into trade mark problems and the name was again changed to nilon. English speakers differed in their pronunciation of this, so, to remove ambiguity the name finally became nylon.
Two years before the basic patent on nylon had been filed, the discoverer of nylon, Wallace Hume Carothers, suffering from one of his increasingly frequent attacks of depression, caused by his conviction that he was a scientific failure, drank juice containing potassium cyanide. He would be pleased to know that half of all the chemists in the US work on the preparation, characterization, or application of polymers.
nylon polymer molecules cross-linked by hydrogen bonds after cold-drawing
Within six years after the accidental spill, a material resembling silk had been produced. His starting material was mulberry leaves, the natural food of silkworms, dissolved in ether and alco hol. He drew the fibers out and coagulated them in warm air. The unveiling of this artificial silk took place at the Paris Exposition of 1891, where the enthusiasm for this product quickly resulted in financial backing to begin commercial production. This new fiber was called 'artificial silk' until 1924 when the name rayon was first used.
This 'artificial silk' was not only used for clothing, but also to produce movie film. There were some significant problems with this fiber, cellulose nitrate, as it was highly flammable. This material's flammability resulted in several disastrous fires in movie theaters when the projector jammed and the film stayed in the path of the intense light for only a few seconds. Because of this, if was replaced with a 'safety film' produced from cellulose acetate.
Newer rayons have been developed. The two most common are xanthate rayon and acetate rayon. The xanthate rayon, regenerated cellulose, it prepared by converting cellulose into a soluble form, cellulose xanthate. This is then extruded through fine holes into a chemical bath that converts the cellulose xanthate back into cellulose. This process gives the regenerated cellulose a smooth, silky finish unlike the fuzzy appearance of cotton, a natural cellulose. Xanthate rayon is found on labels simply as rayon.
The acetate rayon, found on labels as acetate, is prepared in a similar fashion to ChardonnetŐs early rayon. Cellulose is converted to an acetate ester, rather than a nitrate, which is soluble and can be extruded into smooth fibers. This cellulose acetate is not flammable, but is somewhat soluble in organic solvents, such as acetone. The xanthate rayon is impervious to organic solvents.
Organic molecules are among the most important to our lives and society--plastics, fossil fuels and other petroleum products, biological molecules (DNA, proteins, etc.), drugs, dyes, artificial sweeteners (saccharin and aspartame) and new fat 'substitutes' (olestra). Yet many chemistry classes do not include them. We hope the exercises presented here and the guidleines for a unit in organic chemistry will inspire many teachers to include them, to expand their treatment, or to enrich what they already teach with perspectives in the history and philosophy of science.A good warm-up activity is to explore a list of 'Polymers in Everyday Life'.