Silicone, also called polysiloxane, any of a diverse class of fluids, resins, or elastomers based on polymerized siloxanes, substances whose molecules consist of chains made of alternating silicon and oxygen atoms. Their chemical inertness, resistance to water and oxidation, and stability at both high and low temperatures have led to a wide range of commercial applications, from lubricating greases to electrical-wire insulation and biomedical implants (such as breast implants).
Applications
Polysiloxanes are manufactured as fluids, resins, or elastomers, depending on the molecular weight of the polymers and the degree to which the polymer chains are interlinked. Nonvulcanized, low-molecular-weight polysiloxane fluids are exceptionally stable to decomposition by heat, water, or oxidizing agents and are good electrical insulators. They make excellent lubricants and hydraulic fluids, as well as emulsions for imparting water repellency to textiles, paper, and other materials. Silicone resins are used in protective coatings and electrically insulating varnishes and for laminating glass cloth.
Vulcanized silicone rubber is prepared in two principal forms: (1) as room-temperature-vulcanizing (RTV) elastomers, which are low-molecular-weight liquids that are cast or molded into desired shapes and then interlinked at room temperature, and (2) high-temperature-vulcanizing (HTV) elastomers, which are higher-molecular-weight gums that are mixed and processed like other elastomers. Silicone rubbers are usually strengthened by fillers such as silica; other fillers are mixed in to add bulk and colour. Valued for their electrical-insulating properties, chemical stability, and the wide temperature range over which they retain resiliency, silicone rubbers are used mainly in O-rings, heat-resistant seals, caulks, gaskets, electrical insulators, flexible molds, and (owing to their chemical inertness) surgical implants.
History
Siloxanes were first characterized as polymers by the English chemist Frederic Stanley Kipping in 1927. Because Kipping thought that the structure of the repeating unit was essentially that of a ketone (the polymer chains formed by silicon atoms, with oxygen atoms attached by double bonds), he incorrectly called them silicones, a name that has persisted. In 1940 American chemist Eugene George Rochow at the General Electric Company laboratories in Schenectady, N.Y., U.S., prepared methyl siloxanes by the process that remains the basis of modern polymerization methods. Meanwhile, researchers at Corning Glass were exploring the production of silicones, and in 1943 Corning and the Dow Chemical Company formed the Dow Corning Corporation to produce silicone products.