The invention: Synthetic polymers characterized by lubricity, extreme water repellency, thermal stability, and inertness that are widely used in lubricants, protective coatings, paints, adhesives, electrical insulation, and prosthetic replacements for body parts.
The people behind the invention:
Eugene G. Rochow (1909- ), an American research chemist Frederic Stanley Kipping (1863-1949), a Scottish chemist and professor
James Franklin Hyde (1903- ), an American organic chemist
Synthesizing Silicones
Frederic Stanley Kipping, in the first four decades of the twentieth century, made an extensive study of the organic (carbon-based) chemistry of the element silicon. He had a distinguished academic career and summarized his silicon work in a lecture in 1937 (“Organic Derivatives of Silicon”). Since Kipping did not have available any naturally occurring compounds with chemical bonds between carbon and silicon atoms (organosilicon compounds), it was necessary for him to find methods of establishing such bonds. The basic method involved replacing atoms in naturally occurring silicon compounds with carbon atoms from organic compounds.
While Kipping was probably the first to prepare a silicone and was certainly the first to use the term silicone, he did not pursue the commercial possibilities of silicones. Yet his careful experimental work was a valuable starting point for all subsequent workers in organosilicon chemistry, including those who later developed the silicone industry.
On May 10, 1940, chemist Eugene G. Rochow of the General Electric (GE) Company’s corporate research laboratory in Schenectady, New York, discovered that methyl chloride gas, passed over a heated mixture of elemental silicon and copper, reacted to form compounds with silicon-carbon bonds. Kipping had shown that these silicon compounds react with water to form silicones.
The importance of Rochow’s discovery was that it opened the way to a continuous process that did not consume expensive metals, such as magnesium, or flammable ether solvents, such as those used by Kipping and other researchers. The copper acts as a catalyst, and the desired silicon compounds are formed with only minor quantities of by-products. This “direct synthesis,” as it came to be called, is now done commercially on a large scale.
Silicone Structure
Silicones are examples of what chemists call polymers. Basically, a polymer is a large molecule made up of many smaller molecules that are linked together. At the molecular level, silicones consist of long, repeating chains of atoms. In this molecular characteristic, sili-cones resemble plastics and rubber.
Silicone molecules have a chain composed of alternate silicon and oxygen atoms. Each silicon atom bears two organic groups as sub-stituents, while the oxygen atoms serve to link the silicon atoms into a chain. The silicon-oxygen backbone of the silicones is responsible for their unique and useful properties, such as the ability of a silicone oil to remain liquid over an extremely broad temperature range and to resist oxidative and thermal breakdown at high temperatures.
A fundamental scientific consideration with silicone, as with any polymer, is to obtain the desired physical and chemical properties in a product by closely controlling its chemical structure and molecular weight. Oily silicones with thousands of alternating silicon and oxygen atoms have been prepared. The average length of the molecular chain determines the flow characteristics (viscosity) of the oil. In samples with very long chains, rubber-like elasticity can be achieved by cross-linking the silicone chains in a controlled manner and adding a filler such as silica. High degrees of cross-linking could produce a hard, intractable material instead of rubber.
The action of water on the compounds produced from Rochow’s direct synthesis is a rapid method of obtaining silicones, but does not provide much control of the molecular weight. Further development work at GE and at the Dow-Corning company showed that the best procedure for controlled formation of silicone polymers involved treating the crude silicones with acid to produce a mixture
Eugene G. Rochow
Eugene George Rochow was born in 1909 and grew up in the rural New Jersey town of Maplewood. There his father, who worked in the tanning industry, and his big brother maintained a small attic laboratory. They experimented with electricity, radio—Eugene put together his own crystal set in an oatmeal box—and chemistry.
Rochow followed his brother to Cornell University in 1927. The Great Depression began during his junior year, and although he had to take jobs as lecture assistant to get by, he managed to earn his bachelor’s degree in chemistry in 1931 and his doctorate in 1935. Luck came his way in the extremely tight job market: General Electric (GE) hired him for his expertise in inorganic chemistry.
In 1938 the automobile industry, among other manufacturers, had a growing need for a high-temperature-resistant insulators. Scientists at Corning were convinced that silicone would have the best properties for the purpose, but they could not find a way to synthesize it cheaply and in large volume. When word about their ideas got back to Rochow at GE, he reasoned that a flexible silicone able to withstand temperatures of 200 to 300 degrees Celsius could be made by bonding silicone to carbon. His research succeeded in producing methyl silicone in 1939, and he devised a way to make it cheaply in 1941. It was the first commercially practical silicone. His process is still used.
After World War II GE asked him to work on an effort to make aircraft carriers nuclear powered. However, Rochow was a Quaker and pacifist, and he refused. Instead, he moved to Harvard University as a chemistry professor in 1948 and remained there until his retirement in 1970. As the founder of a new branch of industrial chemistry, he received most of the discipline’s awards and medals, including the Perkin Award, and honorary doctorates.
from which high yields of an intermediate called “D4″ could be obtained by distillation. The intermediate D4 could be polymerized in a controlled manner by use of acidic or basic catalysts. Wilton I. Patnode of GE and James F. Hyde of Dow-Corning made important advances in this area. Hyde’s discovery of the use of traces of potassium hydroxide as a polymerization catalyst for D4 made possible the manufacture of silicone rubber, which is the most commercially valuable of all the silicones.
Impact
Although Kipping’s discovery and naming of the silicones occurred from 1901 to 1904, the practical use and impact of silicones started in 1940, with Rochow’s discovery of direct synthesis.
Production of silicones in the United States came rapidly enough to permit them to have some influence on military supplies for World War II (1939-1945). In aircraft communication equipment, extensive waterproofing of parts by silicones resulted in greater reliability of the radios under tropical conditions of humidity, where condensing water could be destructive. Silicone rubber, because of its ability to withstand heat, was used in gaskets under high-temperature conditions, in searchlights, and in the engines on B-29 bombers. Silicone grease applied to aircraft engines also helped to protect spark plugs from moisture and promote easier starting.
After World War II, the uses for silicones multiplied. Silicone rubber appeared in many products from caulking compounds to wire insulation to breast implants for cosmetic surgery. Silicone rubber boots were used on the moon walks where ordinary rubber would have failed.
Silicones in their present form owe much to years of patient developmental work in industrial laboratories. Basic research, such as that conducted by Kipping and others, served to point the way and catalyzed the process of commercialization.
See also Buna rubber; Neoprene; Nylon; Plastic; Polystyrene; Teflon.
