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Silicone resins are a type of
Silicone resins are a type of silicone
In Organosilicon chemistry, organosilicon and polymer chemistry, a silicone or polysiloxane is a polymer composed of repeating units of siloxane (, where R = Organyl group, organic group). They are typically colorless oils or elastomer, rubber ...
material which is formed by branched, cage-like oligosiloxanes with the general formula of where R is a non-reactive substituent
In organic chemistry, a substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule.
The suffix ''-yl'' is used when naming organic compounds that contain a single bond r ...
, usually methyl
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated as ...
(Me = ) or phenyl
In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula , and is often represented by the symbol Ph (archaically φ) or Ø. The phenyl group is closely related to benzene and can be viewed as a benzene ...
(Ph = ), and X is a functional group
In organic chemistry, a functional group is any substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions r ...
: hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
(), hydroxyl
In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...
(), chlorine
Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
() or alkoxy
In chemistry, the alkoxy group is an alkyl group which is Single bond, singularly bonded to oxygen; thus . Denoted usually with apostrophe('). The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the ...
(). These groups are further condensed in many applications, to give highly crosslinked
In chemistry and biology, a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
, insoluble polysiloxane networks.S.J. Clarson, J.A. Semlyen, ''Siloxane Polymers'', Prentice Hall, New Jersey (1993).
When R is methyl, the four possible functional siloxane monomeric units are described as follows:
* "M" stands for trimethylsilanol
Trimethylsilanol (TMS) is an organosilicon compound with the formula . The Si centre bears three methyl groups and one hydroxyl group. It is a colourless volatile liquid.Paul D. Lickiss: ''The Synthesis and Structure of Organosilanols'', Advances i ...
, ;
* "D" for ;
* "T" for ;
* "Q" for .
Note that a network of only Q groups becomes fused quartz
Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses, such as soda-lime glass, lead glass, or borosi ...
.
The most abundant silicone resins are built of D and T units (DT resins) or from M and Q units (MQ resins); however, many other combinations (MDT, MTQ, QDT) are also used in industry.
Silicone resins represent a broad range of products. Materials of molecular weight in the range of 1000–10,000 are very useful in pressure-sensitive adhesives, silicone rubbers, coatings, and additives. Polysiloxane polymers with reactive side group functionality such as vinyl, acrylate, epoxy, mercaptan, or amine, are used to create thermoset polymer matrix composites, coatings, and adhesives.
Silicone resins are prepared by hydrolytic
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysis ...
condensation
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor ...
of various silicone precursors. In early processes of preparation of silicone resins, sodium silicate
Sodium silicate is a generic name for chemical compounds with the formula or ·, such as sodium metasilicate (), sodium orthosilicate (), and sodium pyrosilicate (). The anions are often polymeric. These compounds are generally colorless tra ...
and various chlorosilanes were used as starting materials. Although the starting materials were the least expensive ones (something typical for industry), structural control of the product was very difficult. More recently, a less reactive tetraethoxysilane - (TEOS) or ethyl polysilicate and various disiloxanes are used as starting materials.
Microbial deterioration
The algae Stichococcus bacillaris and certain fungal species have been seen to colonize silicone resins used at archaeological sites.See also
* Water glass (Sodium silicate, .e.g Na2SiO3 etc.) *Silicone rubber
Silicone rubber is an elastomer composed of silicone—itself a polymer—containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations. Silicone rubbers ar ...
References
* Synthetic resins * {{Chem-stub de:Silikonharz