What Is Silicone?

The synthetic polymer is used in shoe insoles, breast implants, and deodorant

Blanchi Costela/Getty Images.

Silicones are a type of synthetic polymer, a material made of smaller, repeating chemical units called monomers that are bonded together in long chains. Silicone consists of a silicon-oxygen backbone, with “sidechains” consisting of hydrogen and/or hydrocarbon groups attached to the silicon atoms. Because its backbone does not contain carbon, silicone is considered an inorganic polymer, which differs from the many organic polymers whose backbones are made of carbon.

The silicon-oxygen bonds in the silicone backbone are highly stable, binding together more strongly than the carbon-carbon bonds present in many other polymers. Thus, silicone tends to be more resistant to heat than conventional, organic polymers.

Silicone’s sidechains render the polymer hydrophobic, making it useful for applications that may require repelling water. The sidechains, which most commonly consist of methyl groups, also make it difficult for silicone to react with other chemicals and prevents it from sticking to many surfaces. These properties can be tuned by changing the chemical groups attached to the silicon-oxygen backbone.

Silicone in Everyday Life

Silicone is durable, easy to manufacture, and stable over a wide range of chemicals and temperatures. For these reasons, silicone has been highly commercialized and is used in many industries, including automotive, construction, energy, electronics, chemical, coatings, textiles, and personal care. The polymer also has a variety of other applications, ranging from additives to printing inks to the ingredients found deodorants.

Discovery of Silicone

The chemist Frederic Kipping first coined the term “silicone” to describe compounds he was making and studying in his laboratory. He reasoned that he should be able to make compounds similar to the ones that could be made with carbon and hydrogen, since silicon and carbon shared many similarities. The formal name for describing these compounds was “silicoketone,” which he shortened to silicone.

Kipping was far more interested in accumulating observations about these compounds than figuring out exactly how they worked. He spent many years preparing and naming them. Other scientists would help discover the fundamental mechanisms behind silicones.

In the 1930s, a scientist from the company Corning Glass Works was trying to find a proper material to include in insulation for electrical parts. Silicone worked for the application due to its ability to solidify under heat. This first commercial development led silicone to be widely manufactured.

Silicone vs. Silicon vs. Silica

Though “silicone” and “silicon” are spelled similarly, they are not the same.

Silicone contains silicon, an atomic element with an atomic number of 44. Silicon is a naturally occurring element with many uses, most notably as a semiconductors in electronics. Silicone, on the other hand, is manmade and does not conduct electricity, as it is an insulator. Silicone cannot be used as part of a chip inside a cell phone, though it is a popular material for cell phone cases.

"Silica," which sounds like “silicon,” refers to a molecule consisting of a silicon atom joined to two oxygen atoms. Quartz is made of silica.

Types of Silicone and Their Uses

There are several different forms of silicone, which vary in their degree of crosslinking. The degree of crosslinking describes how interconnected the silicone chains are, with higher values resulting in a more rigid silicone material. This variable alters properties such as the strength of the polymer and its melting point.

The forms of silicone, as well as some of their applications, include:

  • Silicone fluids, also called silicone oils, consist of straight chains of the silicone polymer with no crosslinking. These fluids have found use as lubricants, paint additives, and ingredients in cosmetics.
  • Silicone gels have few crosslinks between the polymer chains. These gels have been used in cosmetics and as a topical formulation for scar tissue, since silicone forms a barrier that helps the skin stay hydrated. Silicone gels are also used as as materials for breast implants and the soft part of some shoe insoles.
  • Silicone elastomers, also called silicone rubbers, include even more crosslinks, yielding a rubberlike material. These rubbers have found use as insulators in the electronics industry, seals in aerospace vehicles, and oven mitts for baking.
  • Silicone resins are a rigid form of silicone and with a high crosslinking density. These resins have found use in heat-resistant coatings and as weather-resistant materials for protecting buildings.

Silicone Toxicity

Because silicone is chemically inert and more stable than other polymers, it is not expected to react with parts of the body. However, toxicity depends upon factors such as exposure time, chemical composition, dose levels, type of exposure, absorption of the chemical, and the individual response. 

Researchers have examined the potential toxicity of silicone by looking for effects such as skin irritation, changes in the reproductive system, and mutations. Although a few types of silicone showed potential to irritate human skin, studies have shown that exposure to standard quantities of silicone typically produce few to no adverse effects.

Key Points

  • Silicone is a type of synthetic polymer. It has a silicon-oxygen backbone, with “sidechains” consisting of hydrogen and/or hydrocarbon groups attached to the silicon atoms.
  • The silicon-oxygen backbone makes silicone more stable than the polymers that have carbon-carbon backbones. 
  • Silicone is durable, stable, and easy to manufacture. For these reasons, it has been widely commercialized and is found in many everyday items. 
  • Silicone contains silicon, which is a naturally-occurring chemical element.
  • The properties of silicone change as the degree of crosslinking increases. Silicone fluids, which have no crosslinking, are the least rigid. Silicone resins, which have a high level of crosslinking, are the most rigid. 

Sources

Freeman, G. G. “The versatile silicones.” The New Scientist, 1958.

“” In Safety of Silicone Breast Implants, ed. Bondurant, S., Ernster, V., and Herdman, R. National Academies Press, 1999.

"Silicones." The Essential Chemistry Industry.

Shukla, B., and Kulkarni, R. "Silicone polymers: history & chemistry."

“The Technic explores silicones.” The Michigan Technic, vol. 63-64, 1945, pp. 17.

Wacker. Silicones: Compounds and properties.