Isoprene

Isoprene

     Although rubber has been known about for centuries, it has only been essential to civilization for the past 150 years. Indian tribe is from the Amazon basin are credited with the first use of rubber. Christopher Columbus saw Indians in Hispaniola playing with high-bouncing balls made from a tree gum. He observed that they bounced better than the balls in Spain, and took a sample of the material home. The rubber latex was not suited for the environment in Europe, as it would become hard and brittle during the winter and sticky and smelly in hot weather. Charles-Marie de La Condamine of France was hired by the French Academy of Sciences to see if this substance had a use. He traveled to the South American jungle, and saw Omegus Indians from Ecuador collecting white sap from the caoutchouc tree (the material the. alls were made from). The Indians then held the sap over smokey fire, and molded it into various shapes. La Condamine's raw sample, however, was not preserved by smoking, so it arrived in Europe as a smelly mass that could not be used. Latex is a colloidal emulsion, meaning it is "a suspension of natural rubber particles in water".

Cis form

Trans form

     Natural rubber is a polymer of isoprene, the smallest repeating unit of polymer, which contains five carbon atoms. Michael Faraday performed the first experiments on rubber, and in 1826 he determined that the chemical formula for rubber is a multiple of C5H8. Isoprene was able to be distilled from rubber by 1835, which suggested that isoprene was composed of repeating C5H8 units. Isoprene has cis and trans structures, which create major differences in the properties of the molecule. When isoprene molecules are arranged in the cis form, the resulting rubber is very elastic. However, if the molecules are in a trans arrangement, the resulting polymer has properties vastly different than those of rubber. This polymer naturally occurs in balata and gutta-percha. These materials are both made from latex, and they can be melted and molded. Unfortunately, after being exposed to the air for a while, they become hard.
     Charles Macintosh used naphtha to convert rubber into a fabric coating in 1823, which was used to produce waterproof coats. However, the popularity of these "macintoshes" (raincoats) decreased when people saw that they became brittle in the winter and melted in the summer. The word rubber was created by Joseph Priestley in 1770, when he discovered that caoutchouc rubbed out pencil marks better than the moist bread method previously used. Around 1834, Charles Goodyear, American inventor and entrepreneur (but mostly inventor), had an idea that mixing rubber with a dry powder would help to absorb the extra moisture that made it so sticky in the heat. Goodyear began experimenting with different substances, but nothing worked. In the winter of 1839, he was experimenting with powdered sulfur and rubber when he accidentally dropped some of the mixture on a hot stove. Goodyear was surprised to see that the heat and sulfur changed rubber the way he had hoped. After continued experiments with adding sulfur and heat to rubber, Goodyear finally created a rubber that remained elastic, tough, and stable in any weather. 

     Goodyear did not know why rubber was affected by heat and sulfur in this way, but he named his process "vulcanization" after the Roman god of fire. It wasn't for at least another 70 years until Samuel Shrowder Pickles proposed that rubber was a polymer of isoprene in a linear arrangement. The addition of sulfur created cross-links through the bonds between sulfurs. Heat helped form these bonds, which hold rubber molecules in place while allowing them to remain flexible.

     In 1876, Henry Alexander Wickham left the Amazon on a ship with 70 thousand seeds of Hevea brasiliensis, the major source of rubber latex. He arrived at the home of Joseph Hooker, a famous botanist. A propagating house was set up, and the seeds were planted. Western Malaysia is the home of the first two rubber plantations. By 1896, London received Malayan rubber, and Britain had 10 million rubber trees by 1907. Leopold II of Belgium colonized central Africa in the 1880s, and demanded red rubber as ransom from the African people. Those who did not collect enough rubber often had their hands cut off.
     98 percent of the world's rubber supply was being produced by plantations in Southeast Asia by 1932. After the attack on Pearl Harbor in 1941, President Franklin Delano Roosevelt established a commission to search for solutions to the wartime rubber shortage. The commission concluded that without securing a vast amount of rubber, the mission would fail. Roosevelt determined that dandelions would produce small amounts of questionable latex. The best solution was to produce synthetic rubber. An isoprene polymer similar to rubber is found naturally in latex. It is known as "chicle", and it had been used for chewing gum since ancient times. Chicle was introduced to the United States in 1855, when General Antonio Lopez de Santa Anna was exiled from Mexico. He had hoped to sell chicle to American rubber interests to earn money to raise a militia and reclaim his presidency of Mexico. Santa Anna worked with Thomas Adams, but they could not vulcanize chicle or blend it with rubber. However, Adams remembered its use as chewing gum, and he produced flavored chewing gum based on chicle. This was the start of the chewing gum industry.
     The technology to create synthetic rubber came from Germany. When the Allies blockaded Germany's supply of natural rubber during World War I, the German company IG Farben began producing rubber-like products, including styrene butadiene rubber (SBR). In 1929, the Standard Oil Company in New Jersey partnered with IG Farben, with an agreement that Standard Oil received access to specific IG Farben patents, including the one for SBR. IG Farben did not have to disclose all technical details, and in 1938 the Nazi government told the company not to give the United States any information on the rubber-making process. However, IG Farben eventually gave Standard Oil access to the patent under the belief that it did not have enough information for the United States to make their own rubber. They were wrong, and by 1945 the United States was producing over 800,000 tons of rubber- the second greatest feat of engineering (after the atomic bomb). In 1953, Karl Ziegler and Giulio Natta were able to independently develop processes that created either trans or cis double bonds, depending on the catalyst that was used. This made it possible to synthetically produce natural rubber. Ziegler and Natta received the Nobel Prize in chemistry for their work.