Elastomeric Materials
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Elastomeric Materials Because rubber plants occur naturally in only a few out-of-the way places around the world—such as Malaya, South America, and Indonesia—attempts to create synthetic materials with the useful properties of rubber began a century and a half ago. The many investigations eventually resulted in a variety of new elastomeric materials and also laid the basic foundations for polymer chemistry. Chemists finally succeeded in synthesizing the actual rubber molécule in the late 1950s, but by that rime other elastomers had found broad applications in Worldwide technology and industry. The synthesis of rubber from other raw materials could not begin until the basic chemistry of the substance was better understood. In 1826 in England, Michael Faraday made one of the first chemical analyses of natural rubber, interpreting its molecular formula as C5H8. With this knowledge, many other hopeful researchers attempted to build synthetic rubber molécules that could be produced easily and inexpensively. In 1838 in Germany, EC. Himly was able to obtain a volatile distillate from natural rubber, and in 1860 in England, chemist C.G. Williams went further and distilled natural rubber into three parts, oil, tar, and "spirit" (the volatile fraction). He named the "spirit" isoprene. The next step was to see if isoprene could be synthesized from readily available raw materials and then converted back into rubber. In France, Georges Bouchardat used hydrogen chloride gas in 1875 in a prolonged distillation of isoprene, which yielded a rubberlike substance. This was one of the first synthetic elastomers ever created. In 1882 in England, W.A. Tilden produced isoprene through the destructive distillation of turpentine, rather than any raw material that came from natural rubber. He reported that, after storage or through the action of chemical agents, his spécimens of isoprene changed into a material that resembled rubber. The search for substitutes for natural rubber did not make major progress until researchers stopped trying to reproduce the exact chemical composition of rubber, and instead concentrated on synthesizing materials with similar properties. Such rubbery materials, with chemical structures very différent from rubber, required a more gênerai désignation, though: "Elastomer," a contraction ofelastic and polymer, was defined as a substance
MRS BULLETIN/JUNE1990
that can be stretched at room température to at least twice its original length and, after being stretched, rapidly returns to approximately its original length when the stress is removed. For a material to exhibit elastomeric properties, it must hâve long threadlike molécules, flexibility in the molecular chain to allow stretching and coiling, and some form of chemical or mechanical bonds between the molécules. Petroleum has been the most important raw material for creating synthetic elastomers; some synthetic rubbers also use potatœs and grains (and the alcohol produced by them), coke, limestone, sait, and sulfur. Germany and Russia, who had no ready access
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