November 2004

What do automobile tires, wetsuits, and soft coatings on exercise weights have in common? They are all made of neoprene, the first successful synthetic rubber product ever made. Invented in 1930 by DuPont company scientists (and first known as "Duprene"), 300,000 tons of neoprene are produced worldwide every year. Neoprene finds its way into many of the products we rely on every day.

The technical name for this synthetic rubber is polychloroprene. Polychloroprene is an organic compound, which means it is mostly composed of carbon and hydrogen atoms. And it is a polymer, or long-chained molecule, formed by linking together, end-on-end, many smaller molecules known as monomers. In this case, the monomers are chloroprene, C4H5Cl:

Dr. Chainsworth Weighs in on Neoprene

Organic chemist Dr. Linky Chainsworth met with us recently to discuss neoprene. She was happy to talk about this polymer, which she calls "an oldie, but goodie."

"Neoprene is actually more resistant than natural rubber to water, oils, solvents and heat, so it is very useful. During World War II, in fact, all of the neoprene made in the U.S. went to the war effort for making necessary products: tires, fan belts, hoses, seals and gaskets for vehicles, and gear of many types. The public had to do without neoprene until after the war."

Chemical Properties Made to Order

Linky also told us that the chemical and physical properties of neoprene can be changed with a few chemical tweaks to the polymer structure. One of these tweaks, she said, is "vulcanization," a process named for the Roman god of fire.

Linky explained that vulcanization was invented by Charles Goodyear back in 1839. "Mr. Goodyear worked very hard to improve the properties of natural rubber-a natural polymer-which is too responsive to changes in temperature--sticky in the summer and hard and brittle in the winter. One lucky day, after accidentally leaving some natural rubber and sulfur on his stove and burning it, Goodyear found that the rubber had hardened and become melt-resistant and more elastic. Finally, he had the key to making natural rubber more useful."

Vulcanization-Cross-Linking Polymer Chains

We asked Linky to explain what happens chemically during vulcanization of chloroprene. "Before vulcanization," she answered, "chloroprene molecules are joined end-on-end, forming long chains that are unconnected to one another. During vulcanization, another type of joining takes place--'atomic bridges' of sulfur are formed between the chains. These are called cross-links. When all the chains are cross-linked, the result is one giant supermolecule!" Linky sketched the following "before and after vulcanization" diagrams:

Diagram of Polychlorprene before Vulcanization

Diagram of Polychlorprene after Vulcanization

"Cross-linking by vulcanization improves neoprene. While the basic composition of neoprene remains the same, modifying its structure creates a family of neoprene materials with a wide range of properties. For example, the number of sulfur cross-links generally determines the strength and hardness of neoprene. Manufacturers can choose the neoprene with the most desired characteristics for each job."

April, 1930: Chemical History is Made

Almost 75 years ago, natural rubber was in great demand in the U.S., causing rubber prices to rise. Chemical companies began looking for a synthetic rubber to satisfy the new demand. About this time, the DuPont Company organized a basic chemistry research group, led by an extraordinary young chemist named Wallace Carothers. One of the pioneers of polymer science, Carothers had been a Harvard professor but did not enjoy lecturing students, so he decided to accept a research position offered to him by DuPont. The idea of corporations having their own basic research programs, similar to those in universities, was very new at that time.

The idea turned out to be a good one: The team's first major success was the invention of neoprene in April of 1930. Remarkably, in the same month, the group invented another substance that would eventually be adapted to become the synthetic fabric known as nylon. To this day, corporate research programs continue to make huge contributions to science.

Follow-Up Questions:

  1. Identify five items in your daily life that are made of neoprene.

  2. Vulcanized rubbers, such as neoprene, are called "thermoset" materials because vulcanization, like baking a cake, is an irreversible process. Look up the term "thermoplastic." Define and contrast "thermoplastic" materials with "thermoset" materials, using examples.

  3. What is the monomer found in natural rubber? Diagram the process of rubber production, from its natural source to its many uses.
  4. For a list of previous "Chlorine Compound of the Month" features, click here.

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