Silicone

In organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (−O−R₂Si−O−SiR₂−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cooking utensils, thermal insulation, and electrical insulation. Some common forms include silicone oil, grease, rubber, resin, and caulk.

Silicone is often confused with one of its constituent elements, silicon, but they are distinct substances. Silicon is a pure chemical element, a metalloid, which forms a dark-grey semiconducting crystalline solid. In its crystalline form it is used to make integrated circuits ("electronic chips") and solar cells. In contrast, silicone is formed by the polymerization of the siloxane molecule, which itself is made up of a variable combination of carbon, hydrogen, oxygen and silicon atoms. Depending on the chemical makeup and polymer structure of a particular silicone product, it can possess a variety of physical properties, ranging from an oily liquid to a rubbery resin.

F. S. Kipping coined the word silicone in 1901 to describe the formula of polydiphenylsiloxane, Ph₂SiO (Ph = phenyl, C₆H₅), by analogy with the formula of the ketone benzophenone, Ph₂CO (his term was originally silicoketone). Kipping was well aware that polydiphenylsiloxane is polymeric whereas benzophenone is monomeric and noted the contrasting properties of Ph₂SiO and Ph₂CO. The discovery of the structural differences between Kipping's molecules and the ketones means that silicone is no longer the correct term (though it remains in common usage) and that the term siloxane is preferred according to the nomenclature of modern chemistry.

James Franklin Hyde was an American chemist and inventor. He has been called the "Father of Silicones" and is credited with the launch of the silicone industry in the 1930s. His most notable contributions include his creation of silicone from silicon compounds and his method of making fused silica, a high-quality glass later used in aeronautics, advanced telecommunications, and computer chips. His work led to the formation of Dow Corning, an alliance between the Dow Chemical Company and Corning Glass Works that was specifically created to produce silicone products.

Alfred Stock and Carl Somiesky examined the hydrolysis of dichlorosilane, a reaction that was proposed to initially give the monomer H₂SiO:

When the hydrolysis is performed by treating a solution of H₂SiCl₂ in benzene with water, the product was determined to have the approximate formula [H₂SiO]₆. Higher polymers were proposed to form with time.

Most polysiloxanes feature organic substituents, e.g., [(CH₃)₂SiO]_n and [(C₆H₅)₂SiO)]_n. All polymerized siloxanes or polysiloxanes, silicones consist of an inorganic silicon–oxygen backbone chain (···−Si−O−Si−O−Si−O−···) with two groups attached to each silicon center. The materials can be cyclic or polymeric. By varying the −Si−O− chain lengths, side groups, and crosslinking, silicones can be synthesized with a wide variety of properties and compositions. They can vary in consistency from liquid to gel to rubber to hard plastic. The most common siloxane is linear polydimethylsiloxane (PDMS), a silicone oil.^{[citation needed]} The second-largest group of silicone materials is based on silicone resins, which are formed by branched and cage-like oligosiloxanes.^{[citation needed]}

Most common are materials based on polydimethylsiloxane, which is derived by hydrolysis of dimethyldichlorosilane. This dichloride reacts with water as follows: