Chapter 8: Isoprene

Where would the world be today without rubber? There would be no tires, no gaskets or fan belts, no elastic for clothes, no waterproof soles for shoes, and no rubber bands. The birth of rubber came from the gum of the caoutchouc tree. During the 18th century. French Exploror, Chales-Marie de La Condamine observed the Omegus Indians collecting the caoutchoc sap, holding it over a smokey fire and molding the sap into different shapes. But when La Condamine tried to send samples of the caoutchoc sap over seas back to France, it fermented in the hot weather and by the time it arrived in Europe, it was a sticky, smelly mess. This was a problem of rubber for many years to come. The various rubber compounds would become hard and brittle during the winter, and would melt during the hot summer months. In 1839, nearly 100 years after the caoutchoc sap's discovery and numerous other failed attempts at forming viable rubber compounds, Charles Goodyear discovered that adding powdered sulfur to rubber could absorb the excess moisture that made the substance sticky during the summer. (Le Couteur & Burreson 141-161)

Natural rubber is a polymer of Isoprene. Isoprene is the smallest repeating unit of any natural polymer and therefore, makes rubber the simplest natural polymer. The chemical formula for rubber was discovered to be C5H8. There are two forms of the isoprene molecule: cis and trans. In the cis structure of isoprene, the two hydrogen atoms are on the same side of the double bond. In the trans structure, the two hydrogen atoms are on different sides of the double bond. The arrangement of these molecules vastly affects the end result's properties. For example, the cis arrangement of isoprene is essential for the elasticity of some rubbers, while the trans formation yields the stiff and tough properties of some other rubbers. The molecular structure forms a cross-linkage that holds the rubber together. In the cis formation, there is not enough cross linking between the molecules and they are able to slip past each other, resulting in the flexibility and stretchiness of cis rubber. In the trans formation, there is more cross linking and therefore produces a more rigid final product. (Le Couteur & Burreson 141-161)

the cis structure of isoprene

(from xamplified.com)

Rubber, over the course of the 200 years since it was first discovered in the forests of Ecuador, has become a staple in Global Society. It has become a military as well as an industrial necessity. Many times through the course of our day, we forget to recognize the significance that rubber plays on our lives. With out the small rubber gaskets, or hoses, or rubber tires, rubberized waterproof clothing, or something as mundane as rubber bands, our society will come crashing down. (Le Couteur & Burreson 141-161)