Silicones
Silicone is a generic term denoting compounds which have a backbone of alternating silicon and oxygen atoms with additives hanging off the silicon atoms as pendant groups. Silicon and oxygen are the two elements in greatest supply on the Earth's crust.
Silicon was first isolated by Jons J. Berzelius (1779-1848) in its amorphous state in the 1820s. In 1854 Henri-Etienne Sainte-Claire Deville (1818-1881) obtained it in crystalline form. Charles Friedel (1832-1899) researched silicon compounds as part of his search for synthetic diamonds. By 1863 Friedel and his partner, James Crafts (1839-1917), had produced the first organo-silicon compound. Alfred Stock (1876-1946), Albert Ladenburg (1842-1911), and A. Polis all conducted research into carbon-silicon bonds. It was not until Victor Grignard (1871-1935) had discovered Grignard reagents, organo-magnesium compounds, that Frederic Stanley Kipping prepared his first silicone using the Grignard reagents. While there is some doubt as to whether he was the very first to form a silicone, he was the first to use the term.
Kipping was an English chemist born in Manchester, England. He attended Owens College in Manchester and graduated with a chemistry degree. He then moved on to the University of Munich and worked in Adolf von Baeyer's (1835-1917) laboratory as a graduate student, receiving his doctorate degrees from the University of Munich and the University of London in 1887.
Kipping's use of Grignard reagents to form silicones led him to further research the compounds. He conducted many experiments trying to synthesize a double-bonded silicone compound. He never succeeded, but he published more than 50 papers on silicones that laid the foundation for the industry, which today manufactures over 500,000 tons of silicone for use in a wide range of products.
It was not until the 1940s that the silicone industry was able to make use of Kipping's research. In 1940 E.G. Rochow, a chemist with the General Electric Company, discovered an easy way to form silicones. He combined methyl chloride gas and heated silicon and copper to form compounds with silicon-carbon bonds. Earlier research by Kipping proved that these compounds could be reacted with water to form silicones, which owe their great strength and stability to the unique characteristics of the silicon-oxygen bond.
Rochow's discovery and the increased need of certain products during World War II led to a silicone boom. Silicones played important role in the war effort. Electronic equipment, radios, and aircraft spark plugs were waterproofed with silicones. Silicone rubber was used in gaskets for searchlights and for superchargers in aircraft engines.
General Electric, Dow-Corning, Union Carbide, Stauffer Chemical, Wacher-Chemie, and Farbenfabriken Bayer A.G. all began large-scale silicone production within ten years of Rochow's discovery. Other companies soon followed. Further research by James F. Hyde of Dow-Corning led tothe production of silicone rubber.
Silicone rubber material is particularly valuable because its useful temperature range is -178 °F (-117°C) to 600°F (315°C), while the range of natural rubber is -60°F (-51°C) to 180°F (82°C). Silicones today have thousands of applications. They are used primarily as release agents, lubricants, and sealants. Silicone-treated fabrics, bricks, and concrete walls resist water. Silicones in paints give improved weatherability. They are used as electrical insulation and in oven and aircraft door gaskets. Silicone rubber is used in high-temperature applications and space technology, including astronaut boots. The majority of the silicone produced is used in paper and automobile, and food industries, as well as being used in office and medical equipment.
Silicone has been used in plastic surgery to build nose, cheeks, chin, and other bony structures of the face. Its use for cosmetic and replacement breast implants has been clouded by concern that these implants might cause breast cancer and other health problems. In 1995, a jury awarded $10 million in damages to a woman who alleged that a leaky breast implant manufactured by Dow Corning had caused skin disorders, muscle pain, tremors, incontinence, and other medical problems. By 1997, about 100,000 women had settled lawsuits with manufacturers of silicone implants, and another 500,000 had reserved the right to sue. But in September 1997, a review of scores of medical studies that appeared in The Journal of the National Cancer Institute concluded that there was no evidence that silicone breast implants do indeed breast cancer, and that there is only a slight statistical suggestion that breast implants result in some types of connective tissue disease. All the same, by 1997, vegetable oil and other viscous materials were being studied as implant materials to replace silicone.
This is the complete article, containing 734 words
(approx. 2 pages at 300 words per page).
