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'''Silikon''' (tudi '''polisiloksan''') je polimer siloksana (−R<sub>2</sub>Si−O−SiR<sub>2</sub>−, kjer R predstavlja organsko stransko skupino). Silikonski materiali (silikoni) se pojavljajo v obliki brezbarvnih olj ali gumi podobnih snovi ter kot masti in smole. Najpogosteje se uporabljajo v vlogi tesnil, materialov za lepljenje, maziv, medicinskih in kuhinjskih pripomočkov ter toplotnih in električnih izolatorjev.<ref name=Ullmann/><ref>{{cite book |isbn=9781119631378 |title=Liquid Silicone Rubber: Chemistry, Materials, and Processing |last1=Fink |first1=Johannes Karl |date=5 July 2019}}</ref>

== Kemija ==
Stock in Somieski sta med preučevanjem reakcije hidrolize diklorosilana ugotovila, da se pri reakciji tvori monomer siloksana H<sub>2</sub>SiO:

SiH<sub>2</sub>Cl<sub>2</sub>  +  H<sub>2</sub>O  ->  H<sub>2</sub>SiO  + 2 HCl.

Hidrolizo lahko izvajamo tako, da raztopini diklorosilana v benzenu dodajamo vodo. V tem primeru je večinski produkt polimer s približno formulo [H<sub>2</sub>SiO]<sub>6</sub>, verjetno pa se pri daljšem času izvajanja reakcije tvorijo tudi daljši polimeri.<ref name="Seyferth">Seyferth, D., Prud'Homme, C., Wiseman, G., Cyclic Polysiloxanes from the Hydrolysis of Dichlorosilane, Inorganic Chemistry, 22, 2163-2167</ref>

Osnova vseh polisiloksanov je veriga, v kateri se izmenjujeta silicijev in kisikov atom (…–Si–O–Si–O–Si–O–…) in je včasih sklenjena v krog. Na vsakega izmed silicijevih atomov sta vezani dve stranski skupini, ki sta največkrat organska substituenta – primer takšnih polimerov sta [(CH<sub>3</sub>)<sub>2</sub>SiO]<sub>n</sub> in [(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>SiO)]<sub>n</sub>. Med proizvodnjo silikonov lahko s spreminjanjem dolžine polimerov, stranskih skupin in stopnje zamreženosti sintetiziramo snovi z izjemno raznolikimi lastnostmi, o d tekočin in gelov do mehke gume in trdnih materialov s plastičnimi lastnostmi. Najosnovnejši polisiloksan je linearni polidimetilsiloksan (PDMS), ki je pri sobnih pogojih v tekočem agregatnem stanju. Zelo velika skupina silikonskih materialov so silikonske smole, ki so sestavljene iz zamreženih polimerov, katerih struktura spominja na kletko.

=== Terminologija in zgodovina ===
Beseda ''silikon'' (angl. ''silicone''), ki jo je leta 1901 vpeljal Frederic Stanley Kipping, je nastala kot krajše ime za polidifenilsiloksan ([Ph<sub>2</sub>SiO]<sub>n</sub>). Pri tem se je zgledoval po ketonu benzofenonu (Ph<sub>2</sub>CO), katerega je poimenoval ''silikoketon'' (angl. ''silicoketone''). Kljub takšni analogiji pa je Kipping s preučevanjem lastnosti obeh spojin pokazal, da je  benzofenon monomerna molekula, polidifenilsiloksan pa polimer, kar pomeni, da ''silikon'' ni popolnoma ustrezno poimenovanje.<ref>{{Greenwood&Earnshaw2nd|page=362}}</ref><ref>{{cite journal |author=Frederic Kipping, L. L. Lloyd |journal=[[Journal of the Chemical Society|J. Chem. Soc., Trans.]] |year=1901 |volume=79 |pages=449–459 |doi=10.1039/CT9017900449 |title=XLVII. Organic derivatives of silicon. Triphenylsilicol and alkyloxysilicon chlorides |url=https://zenodo.org/record/1753322}}</ref> Ker je bilo dokazano, da je strukturno polidifenilsiloksan bistveno drugačen od benzofenona, bi bilo glede na kemijsko nomenklaturo namesto ''silikon'' bolj ustrezno uporabljati poimenovanje ''siloksan'', vendar se ta sprememba nikoli ni uveljavila, zato je izraz ''silikon'' v uporabi še danes. <ref name="CincinnatiUniversity2005">{{cite book |author1=James E. Mark |author2=Harry R. Allcock |author3=Robert West |title=Inorganic Polymers |url=https://books.google.com/books?id=7YybTrluKBgC&pg=PA155 |date=24 March 2005 |publisher=Oxford University |isbn=978-0-19-535131-6 |page=155 |url-status=live |archive-url=https://web.archive.org/web/20171218190618/https://books.google.com/books?id=7YybTrluKBgC&pg=PA155 |archive-date=18 December 2017}}</ref>

[[Frederic Kipping|F. S. Kipping]] coined the word ''silicone'' in 1901 to describe the formula of polydiphenylsiloxane, Ph<sub>2</sub>SiO (Ph denoting [[phenyl]], C<sub>6</sub>H<sub>5</sub>), by analogy with the formula of the [[ketone]] [[benzophenone]], Ph<sub>2</sub>CO (his term was originally ''silicoketone''). Kipping was well aware that polydiphenylsiloxane is polymeric{{citation needed|date=June 2022}} whereas benzophenone is monomeric and noted the contrasting properties of Ph<sub>2</sub>SiO and Ph<sub>2</sub>CO.<ref>{{Greenwood&Earnshaw2nd|page=362}}</ref><ref>{{cite journal |author=Frederic Kipping, L. L. Lloyd |journal=[[Journal of the Chemical Society|J. Chem. Soc., Trans.]] |year=1901 |volume=79 |pages=449–459 |doi=10.1039/CT9017900449 |title=XLVII. Organic derivatives of silicon. Triphenylsilicol and alkyloxysilicon chlorides |url=https://zenodo.org/record/1753322}}</ref>  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.<ref name="CincinnatiUniversity2005">{{cite book |author1=James E. Mark |author2=Harry R. Allcock |author3=Robert West |title=Inorganic Polymers |url=https://books.google.com/books?id=7YybTrluKBgC&pg=PA155 |date=24 March 2005 |publisher=Oxford University |isbn=978-0-19-535131-6 |page=155 |url-status=live |archive-url=https://web.archive.org/web/20171218190618/https://books.google.com/books?id=7YybTrluKBgC&pg=PA155 |archive-date=18 December 2017}}</ref>

[[James Franklin Hyde]] (born 11 March 1903) 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. 

Silicone is often confused with [[silicon]], but they are distinct substances.  Silicon is a [[chemical element]], a hard dark-grey [[semiconductor|semiconducting]] [[metalloid]], which in its [[crystal]]line form is used to make [[integrated circuit]]s ("electronic chips") and [[solar cell]]s. Silicones are compounds that contain silicon, carbon, hydrogen, oxygen, and perhaps other kinds of atoms as well, and have many very different physical and chemical properties.

Compounds containing silicon–oxygen double bonds, now called [[silanones]], but which could deserve the name "silicone", have long been identified as [[reaction intermediate|intermediates]] in gas-phase processes such as [[chemical vapor deposition]] in [[microelectronics]] production, and in the [[ceramic forming techniques|formation of ceramics]] by combustion.<ref>{{cite journal |journal=[[Journal of Organometallic Chemistry|J. Organomet. Chem.]] |volume=566 |issue=1–2 |year=1998 |pages=45–59 |title=Matrix isolation infrared and density functional theoretical studies of organic silanones, (CH<sub>3</sub>O)<sub>2</sub>Si=O and (C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>Si=O |author1=V. N. Khabashesku |author2=Z. A. Kerzina |author3=K. N. Kudin |author4=O. M. Nefedov | doi= 10.1016/S0022-328X(98)00726-8}}</ref>  However, they have a strong tendency to polymerize into siloxanes. The first stable silanone was obtained in 2014 by [[Alexander C. Filippou|A. Filippou]] and others.<ref name=filippou>Alexander C. Filippou, Bernhard Baars, Yury N. Lebedev, and Gregor Schnakenburg (2014): "Silicon–Oxygen Double Bonds: A Stable Silanone with a Trigonal‐Planar Coordinated Silicon Center". ''Angewandte Chemie International Edition'', volume 53, issue 2, pages 565–570. {{doi|10.1002/anie.201308433}}.</ref>

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

: ''n''&nbsp;Si(CH<sub>3</sub>)<sub>2</sub>Cl<sub>2</sub> + ''n''&nbsp;H<sub>2</sub>O → [Si(CH<sub>3</sub>)<sub>2</sub>O]<sub>''n''</sub> + 2''n''&nbsp;HCl

The polymerization typically produces linear chains capped with Si−Cl or Si−OH ([[silanol]]) groups.  Under different conditions, the polymer is a cyclic, not a chain.<ref name=Ullmann/>

For consumer applications such as caulks silyl [[acetate]]s are used instead of silyl chlorides.  The hydrolysis of the acetates produces the less dangerous [[acetic acid]] (the acid found in [[vinegar]]) as the reaction product of a much slower curing process. This chemistry is used in many consumer applications, such as silicone [[caulk]] and [[adhesive]]s.

: ''n''&nbsp;Si(CH<sub>3</sub>)<sub>2</sub>(CH<sub>3</sub>COO)<sub>2</sub> + ''n''&nbsp;H<sub>2</sub>O → [Si(CH<sub>3</sub>)<sub>2</sub>O]<sub>''n''</sub> + 2''n''&nbsp;CH<sub>3</sub>COOH

[[Branching (polymer chemistry)|Branches]] or crosslinks in the polymer chain can be introduced by using organosilicone precursors with fewer alkyl groups, such as methyl trichlorosilane and [[methyltrimethoxysilane]]. Ideally, each molecule of such a compound becomes a branch point. This process can be used to produce hard silicone resins. Similarly, precursors with three methyl groups can be used to limit molecular weight, since each such molecule has only one reactive site and so forms the end of a siloxane chain.

=== Combustion ===
When silicone is burned in air or oxygen, it forms solid silica (silicon dioxide, [[silicon dioxide|SiO<sub>2</sub>]]) as a white powder, char, and various gases.  The readily dispersed powder is sometimes called [[silica fume]]. The [[pyrolysis]] of certain polysiloxanes under an [[inert atmosphere]] is a valuable pathway towards the production of amorphous [[silicon oxycarbide]] ceramics, also known as [[polymer derived ceramics]]. Polysiloxanes terminated with functional [[ligands]] such as [[Vinyl group|vinyl]], [[mercapto]] or [[acrylate]] groups have been cross linked to yield [[preceramic polymers]], which can be [[photopolymerization|photopolymerised]] for the [[additive manufacturing]] of [[polymer derived ceramics]] by [[stereolithography]] techniques.<ref>[https://arxiv.org/ftp/arxiv/papers/1905/1905.02060.pdf  Additive manufacturing of ceramics from preceramic polymers]: A versatile stereolithographic approach assisted by thiol-ene click chemistry. ''Additive Manufacturing'', (2019) volume 27, pp. 80–90.</ref>