SILOXANE

Siloxane is a kind of organosilicon compounds which is composed of –Si–O–Si–O– backbones with side chains R attached to the silicon atoms (R2SiO), where R is a hydrogen atom or an organic radical possibly bearing functional groups.

Polymers of siloxanes are referred as silicones, such as polydimethylsiloxane (PDMS), which is the dominant polymer in the silicone industry.

Different kinds of siloxanes and polysiloxanes have been synthesized, aiming at fire-retardant applications.

CAS Number: 63148-62-9

EC  Number: 205-492-2

Molecular Formula: C8H24O2Si3

Molecular Weight: 236.53

Synonyms: polydimethylsiloxane (Mw > 6800 Da), Polydimethylsiloxanes, Siloxanes and Silicones, di-Me, Baysilon, Dimethicone, DiMethyl Polysiloxane, dimethyl polysiloxane, DIMETHYL POLYSILOXANE (ME TERM), Dimethyl Silicone, Dimethyl silicone, dimethyl silicone, dimethyl silicone oil, DIMETHYL SILICONES AND SILOXANES, Dimethyl siloxane, dimethyl siloxane, Dimethyl siloxanes and silicones, dimethyl(oxo)silane, dimethyl-bis(trimethylsilyloxy)silane, Dimethylepolysiloxane, Dimethylpolysiloxane, Dimethylsilicone, dimethylsiloxane, Dimethylsiloxane trimethylsiloxane terminated, Dimethylsiloxane, trymethylsilyloxy terminated, Monomers of Siloxanes and Silicones, di-Methyl , Polidimetylosiloksan, Poly dimethyl siloxanes, poly(dimethylsilooxane), POLY(DIMETHYLSILOXANE), Poly(dimethylsiloxane), poly(dimethylsiloxane), Polydimethyisiloxane, polydimethyl siloxane, Polydimethylsiloxan, polydimethylsiloxan, POLYDIMETHYLSILOXANE, Polydimethylsiloxane, Polydimethylsiloxane,linear, Polydimethylsiloxanes, Polydimetylsiloxan, Polysiloxanes, di-Me, Silicon oil, Silicone antifoam 1430, Silicone Oil, Siloxane, Siloxane, dimethyl, Siloxanes, siloxanes and other silicones (polydimethylsiloxane), SILOXANES AND SILICONES, DI-ME, Siloxanes and Silicones, di-Me, Siloxanes and Silicones, di-Me (CTS) (MAN), Siloxanes and Silicones, di-Me(Polydimethylsiloxanes(PDMS)), Siloxanes and silicones, dimethyl, α,ω-trimethylsilyl terminated polydimethylsiloxane, Dimethylpolysiloxane, MED-360, Dimethicone, Dimethylpolysiloxane, Dimethylpolysiloxane Hydrolyzate (Silicone Oil), KF96, Poly[oxy(dimethylsilylene)], α-[trimethylsilyl]-ω-[(trimethylsilyl)oxy], Polydimethyisiloxane, Polydimethylsiloxan, Polydimethylsiloxane, Polydimethylsiloxane “Silicone Silbione fluids, Polydimethysiloxane Polymer, Polydimetylsiloxan, Silicone oil, 12648-49-6, 12684-12-7, 1471301-69-5, 1669409-87-3, 1669410-33-6, 167748-54-1, 2028348-45-8, 2161362-23-6, 37221-45-7, 39476-41-0, 53125-20-5, 63148-62-9, OCTAMETHYLTRISILOXANE, 107-51-7, Trisiloxane, octamethyl-, Poly(dimethylsiloxane), 1,1,1,3,3,5,5,5-Octamethyltrisiloxane, Dimeticone, dimethyl-bis(trimethylsilyloxy)silane, Dimethicone 350, 63148-62-9, Pentamethyl(trimethylsilyloxy)disiloxane, Dimethylbis(trimethylsiloxy)silane, 9G1ZW13R0G, CHEBI:9147, Trisiloxane, 1,1,1,3,3,5,5,5-octamethyl-, Dimethylbis(trimethylsilyloxy)silane, Dimethicones, Poly(dimethylsiloxane), hydroxy terminated, MFCD00084411, MFCD00134211, MFCD00148360, CCRIS 3198, Poly(dimethylsiloxane), trimethylsiloxy terminated, EINECS 203-497-4, dimeticonum, UNII-9G1ZW13R0G, Dimeticona, FRD 20, Ctamethyltrisiloxane, MFCD00008264, Pentamethyl(trimethylsiloxy)disiloxane, octamethyl-trisiloxane, PDMS, dimethicone macromolecule, VOLASIL DM-1, Silicon Oil for Oil Bath, TRISILOXANE [INCI], DM-FLUID 1.0CS, EC 203-497-4, Octamethyltrisiloxane, 98%, DSSTox_CID_20710, DSSTox_RID_79558, DSSTox_GSID_40710, OS 20 (SILOXANE), SCHEMBL23459, Siliconoil Pharma 100 cSt., Dimethyl polysiloxane, bis(trimethylsilyl)-terminated, Dow Corning High-Vacuum Grease, CHEMBL2142985, DTXSID9040710, CHEBI:31498, CXQXSVUQTKDNFP-UHFFFAOYSA-, KF 96A1, OCTAMETHYLTRISILOXANE [MI], dimethylbis(trimethylsiloxy)siliane, Polydimethylsiloxane, 1000 cSt., alpha-(Trimethylsilyl)-omega-methylpoly(oxy(dimethylsilylene)), [(CH3)3SiO]2Si(CH3)2, Tox21_301002, CO9816, MFCD00165850, Silane, dimethylbis(trimethylsiloxy)-, AKOS015840180, ZINC169747808, Antifoam compound for anhydrous systems, FS-4459, NCGC00164100-01, NCGC00164100-02, NCGC00254904-01, CAS-107-51-7, DB-040764, FT-0631598, FT-0696355, O0257, O9816, C07261, D91850, S12475, A801717, XIAMETER(R) PMX-200 SILICONE FLUID 1 CST, J-001906, Poly(dimethylsiloxane), viscosity 1.0 cSt (25 C), Q2013799, XIAMETER(R) PMX-200 Silicone Fluid 20 CS, 2,2,4,4,6,6-hexamethyl-3,5-dioxa-2,4,6-trisilaheptane, Polydimethylsiloxane, 20,000 cSt. trimethoxysilyl terminated, Polydimethylsiloxane, extreme low volatility, viscosity 1000 cSt., Intermediate viscosity polydimethylsiloxane antifoam emulsion, 20% active, viscosity 1500cst, Intermediate viscosity polydimethylsiloxane antifoam emulsion, 30% active, viscosity 1500cst, Polydimethylsiloxane, trimethylsiloxy terminated, reduced volatility, viscosity 20 cSt., 28349-86-2, Intermediate viscosity polydimethylsiloxane antifoam emulsion, 10% active, viscosity 1000-2000cst, Intermediate viscosity polydimethylsiloxane antifoam emulsion, 10% active, viscosity 800-2000cst, Intermediate viscosity polydimethylsiloxane antifoam emulsion, 20% active, viscosity 1000-2000cst, Intermediate viscosity polydimethylsiloxane antifoam emulsion, 30% active, viscosity 1000-2000cst, Polydimethylsiloxane, trimethylsiloxy terminated, extreme low volatility, viscosity 12.500 cSt., 1112-39-6 [RN], 214-189-4 [EINECS], Dimethoxy(dimethyl)silan [German] [ACD/IUPAC Name], Dimethoxy(dimethyl)silane [ACD/IUPAC Name], Diméthoxy(diméthyl)silane [French] [ACD/IUPAC Name], Dimethoxydimethylsilane, Dimethyldimethoxysilane, DMDMS, MFCD00025691 [MDL number], Silane, dimethoxydimethyl- [ACD/Index Name], VV3641666, 1,1-dimethoxy-1-methyl-1-silaethane, 103735-12-2 [RN], 63148-62-9 [RN], Dimethyl dimethoxysilane, Dimethyldimethoxysilane|Dimethoxydimethylsilane, DIMETHYLPOLYSILOXANE [Wiki], Dow Corning Z-6194 [Trade name], FS-3860, Polydimethylsiloxane [Wiki], A3QDB1RS1C [DBID], 104906_ALDRICH [DBID], 40160_FLUKA [DBID], 556688_ALDRICH [DBID], AY 43-004 [DBID], CD5605 [DBID], KBM 22 [DBID], NSC 93882 [DBID], NSC93882 [DBID], TSL 8112 [DBID], TSL 8117 [DBID], UNII:A3QDB1RS1C [DBID]

A siloxane is a functional group in organosilicon chemistry with the Si−O−Si linkage.

The parent siloxanes include the oligomeric and polymeric hydrides with the formulae H(OSiH2)nOH and (OSiH2)n.

Siloxanes also include branched compounds, the defining feature of which is that each pair of silicon centres is separated by one oxygen (O) atom.

The siloxane functional group forms the backbone of silicones, the premier example of which is polydimethylsiloxane (PDMS).

The functional group R3SiO− (where the three Rs may be different) is called siloxy.

Siloxanes are manmade and have many commercial and industrial applications because of Siloxanes’ hydrophobicity, low thermal conductivity, and high flexibility.

Siloxanes are silicone-based compounds that are generally used for their softening, smoothing, and moistening action.

They make products like deodorants slide on more easily, and leave hair and skin more soft and silky.

Siloxane is a kind of organosilicon compounds which is composed of –Si–O–Si–O– backbones with side chains R attached to the silicon atoms (R2SiO), where R is a hydrogen atom or an organic radical possibly bearing functional groups.

Siloxanes are in products that contain silicon such as silicone baking utensils and pans, baby nipples, and pacifiers, medical devices and implants, water-repellent windshield coating, construction lubricants and sealants as well as deodorant creams and moisturizers.

Siloxanes are a group of substances characterized by a chain of alternating silicon (Si) and oxygen (O) atoms.

Within the group, individual siloxane substances differ in size, weight and shape.

They form the backbone of silicone polymers that are used in a variety of applications such as sealants, adhesives, coatings, plastics, cosmetics, medical devices, hygiene products, food contact materials, and many other industrial applications.

Siloxanes are adaptable species that have found extensive applications as versatile materials for functionalising various surfaces and as building blocks for polymers and hybrid organic-inorganic systems.

The primary goal of this review is to report on and briefly explain the most relevant recent developments related to siloxanes and their applications, particularly regarding surface modification and the synthesis of graft copolymers bearing siloxane or polysiloxane segments.

The key strategies for both functionalisation and synthesis of siloxane-bearing polymers are highlighted, and the various trends in the development of siloxane-based materials and the intended directions of their applications are explored.

Siloxane is compound with a Si-O-Si bond functional group in silicone chemistry.

The parent siloxanes include oligomeric and polymeric hydrides with the formulae H(OSiH2)nOH and (OSiH2)n.

Siloxanes also include branched compounds, in which each pair of silicon centers is separated by one oxygen atom.

The siloxane functional groups form the backbone of the siloxane, a prime example of which is polydimethylsiloxane.

And the functional group (RO)3Si is called siloxy.

Siloxanes are a class of organosilicon compounds with the empirical formula R2SiO, where R is an organic group.

Representative examples are [SiO(CH3)2]n (dimethylsiloxane) and [SiO(C6H5)2]n (diphenylsiloxane), where n is typically > 4.

These compounds can be viewed as a hybrid of both organic and inorganic chemical compounds.

The organic side chains confer hydrophobic properties while the -Si-O-Si-O- backbone is purely inorganic.

The word siloxane is derived from the words Silicon, Oxygen, and alkane.

Siloxanes can be found in products such as cosmetics, deodorant, water repelling windshield coatings, food additives such as those used in certain McDonalds fast food products, and some soaps.

They occur in landfill gas and are being evaluated as alternatives to perchloroethylene for drycleaning.

Perchloroethylene is widely considered environmentally undesirable.

Polymerized siloxanes are commonly known as silicones, although this name is somewhat of a misnomer.

A true silicone group has a double bond between oxygen and silicon (hence the derivation of the word silicone from ketone), and polymerized siloxanes do not contain such groups.

Accordingly, polysiloxane is the preferred name of such compounds among chemists

On a molecular level, siloxanes are a chain of alternating silicon and oxygen atoms with an alkane compound.

They are the building blocks for silicone products and are used in a wide variety of applications: sealants, adhesives, coatings, plastics, cosmetics, hygiene products, and others (Global Silicones Council).

They come in different particle sizes, shapes, chemical groups, and molecular weights.

Siloxanes are popular for many applications because of their flexibility, abrasion resistance, and heat resistance. 

Other properties of this synthetic compound include low chemical reactivity, low toxicity, and excellent resistance to oxygen, ozone, and ultraviolet light.

Aside from their desirable qualities, siloxanes are very problematic in the biogas purification process. 

When products containing siloxane are disposed of into landfills and biogas treatment systems, the lighter weight molecules vaporize and are released into the biogas.

This is a problem because combustion is required in order to utilize biogas as an alternative source of energy. 

During the process of combustion, the siloxanes in the biogas turn into silicon dioxide and sand.

The residual sand can be deposited in the equipment during the combustion stage or preceding stages of the purification process (SWANA Symposium).

The buildup of sand can lead to decreased efficiency, increased operating costs, and equipment failure.

To prevent equipment from being damaged during this process, adsorbents are commonly used to remove siloxanes from the gas stream. 

Siloxane is a kind of organosilicon compounds which is composed of –Si–O–Si–O– backbones with side chains R attached to the silicon atoms (R2SiO), where R is a hydrogen atom or an organic radical possibly bearing functional groups.

Polymers of siloxanes are referred as silicones, such as polydimethylsiloxane (PDMS), which is the dominant polymer in the silicone industry.

Different kinds of siloxanes and polysiloxanes have been synthesized, aiming at fire-retardant applications.

Silicones can be used as fire-retardant agents through direct blending within the polymer matrix, incorporation into porous fillers, or by synthesizing block/graft copolymers including silicone segments.

Cyclic siloxanes (cyclosiloxanes) are basic members of the broad family of silicone materials and are used as building blocks for the production of a diverse array of silicone polymers.

A common denominator for cyclosiloxanes is that they contain repeating units of silicone (Si) and oxygen (O) atoms in a closed loop, giving Siloxane a “cyclic” structure.

This also gives them their unique properties as hybrid inorganic-organic substances.

D4, D5, D6 contain 4, 5 and 6 repeating units respectively.

They are the three main cyclosiloxanes in commercial production and several decades of research have proven that they are safe for human health and the environment.

Applications of Siloxane:

Industry use:

Cyclomethicone is a class of liquid siloxane with low viscosity and high volatility.

Siloxane is a skin emollient and a useful cleaning solvent in some cases.

Cyclomethicone has short backbones that form closed or nearly closed cycles with methyl groups, giving them many of the same properties as dimethicones, but making them become more volatile.

So Siloxane is used in many cosmetics where the ultimate complete evaporation of the siloxane carrier fluid is desired. In this way, Siloxane is useful for products such as deodorants and antiperspirants that need to be applied to the skin but will not be sticky afterwards.

Organic chemistry:

Molecular capsules provide micro spaces within the molecule, where unstable species are protected and can be stabilized.

Cyclic oligomers of trisilanol are considered as transient intermediates in the polycondensation of trialkoxysilanes, resulting in the formation of siloxane networks or ladder polymers.

The preparation and separation of these stable forms of intermediates are not only particularly important for understanding the condensation process, but also important for the modeling of the silica surface in homogeneous systems and further conversion to silicon-based functional materials.

If the condensation reaction of the trialkoxysilane is performed in the nanopore cavity of the self-assembled coordination cage, which shows significant binding ability to the neutral molecule, a cyclic trimer can be prepared as a stable form.

In the selective chemodivergent conversion of aldehydes to esters and secondary alcohols, siloxanes and POPd can be used as reaction switches.

The reaction applies to a series synthesis of aldehydes.

Compared to other methods, this method promotes arylation of aldehydes with aryl siloxanes to provide corresponding secondary alcohols while avoiding the use of transition metal catalysts and aryl fluorosilanes.

Production and Use of Siloxane:

Siloxanes are produced by acid hydrolysis of silanes (e.g. dimethyldichlorosilane, chlorotrimethylsilane) and purification by distillation.

About 200 siloxanes and siloxane derivatives are listed in the inventory of ingredients used in cosmetic products compiled by the European Commission INCI (2000 – quoted from MST 2005).

Globally the total consumption of siloxanes is approximately 850,000 tonnes, with Western Europe accounting for about 296,000 tonnes (Will et al 2003 – quoted from MST 2005).

According to the Danish Product Register, the total amount of siloxanes in imported products and products produced in Denmark are 1269-1483 tonnes and 162-1143 tonnes, respectively (quoted from MST 2005).

Siloxanes are used in processing aids, textile applications, cosmetics, toiletries, medical/pharmaceutical preparations, paper coatings, defoamers, paints, coatings, waxes, mechanical fluids, sealants and rubber.

D5 is used in dry cleaning and in industrial cleaning as an alternative to tetrachloroethylene (US-EPA 2005a).

Cyclic siloxanes are used as precursors in the production of polymers (polydimethylsiloxane).

The polymers contain some residual monomers and are used in industrial and consumer applications, in topical pharmaceutical formulations and in breast implants.

In Denmark the main application areas for siloxanes are sealants for construction (29%), processing aids (15%) and textile applications (12%).

About 175 different siloxane products are registered in the Danish Product Register and include 53 registered as used in sealants and 98 registered as used in paints and lacquers. (MST 2005).

Uses of Siloxane:

Polysiloxanes (silicones), upon combustion in an inert atmosphere, generally undergo pyrolysis to form silicon oxycarbide or silicon carbide (SiC).

By exploiting this reaction, polysiloxanes have been used as preceramic polymers in various processes including additive manufacturing.

Polyvinyl siloxane (vinyl polysiloxane) is used to make dental impressions and industrial impressions.

The use of a poly-siloxane precursor in polymer derived ceramics allows the formation of ceramic bodies with complex shapes, although the significant shrinkage in pyrolysis needs to be taken into account.

Trisiloxanes may be used as diffusion pump fluid.

Environmental occurrence and fate:

No data have been located regarding a natural occurrence of siloxanes. Siloxanes are anthropogenic compounds (HSDB 2005).

Siloxanes enter the environment by a variety of human activities.

In general volatile siloxanes are released into the atmosphere.

Non-volatile siloxane fluids will end up in wastewater and then be directed to wastewater treatment plants.

By the treatment process the siloxanes mainly follow the sludge and are either spread on agricultural fields, incinerated or disposed of for landfills.

Siloxanes in solids will after use most often be disposed of for incineration and are nearly 100% mineralised by this process. 

Incineration plants are not considered significant sources of siloxane releases to the atmosphere.

Siloxanes are resistant to chemical reactions such as oxidation, reduction and photodegradation. 

As varying information exists, Siloxane is not clear whether Siloxane is possible for siloxanes to undergo hydrolysis under environmental conditions..

Air:

The main source of emissions of siloxanes into the air is volatile siloxanes used in cosmetics, wax and polishes.

Volatile cyclosiloxanes used in cosmetic products, are meant to evaporate during use.

Based on American experience, 92% of the volatile siloxanes will be emitted to the air.

No quantitatively information is available, but for the US Siloxane is roughly estimated that between 50 and 200 tonnes volatile siloxanes, used for cosmetics, is released to the air each year.

Once released into the atmosphere the volatile siloxanes may react with hydroxyl radicals.

Half-lives for reaction with hydroxyl radicals in air for D4, D5, and HMDS are 16, 10 and 12 days, respectively.

In Denmark, air concentrations measurements of siloxanes have been taken at four locations of which three were taken outdoors and one was taken inside a sewage treatment plant.

The air concentrations of D4, D5 and D6 were in the range 0.26- 2.4 μg/m3, 0.19-1.3 μg/m3 and 0.07-0.44 μg/m3, respectively.

The measured air concentrations of HMDS were <0.004 μg/m3 (below detection limit). Emission of D4 to indoor air has been associated with new carpets. Water: The non-volatile siloxanes used in cosmetics, toiletries, textile applications, cleaning agents and maintenance will mainly be discharged with wastewater. A few per cent of the siloxanes in waterborne paints may also end up in the sewage system by washing of brushes and paint pots. In Denmark, the total release of nonvolatile siloxane fluids to wastewater is estimated at 200-700 tonnes/year. During the treatment processes in treatment plants, approximately 97% of polydimethylsiloxanes will be bound to the sludge. The remaining will be discharged to surface water. In Denmark, concentrations of siloxanes in surface water have been measured at three locations. The concentrations of D4, D5, D6 and HMDS were <0.04 μg/L, <0.02 μg/L, <0.02 μg/L and <0.0005 μg/L, respectively. In Denmark, concentrations of siloxanes in sludge have been measured at two locations. The concentrations of D4, D5, D6 and HMDS were in the range 470-740 ng/g dry weight (dw), 27000-50000 ng/g dw, 1100-2800 ng/g dw and <1-<3 ng/g dw, respectively. In Denmark, concentrations of siloxanes in sediment have been measured at three locations. The concentrations of D4, D5, D6 and HMDS were in the range <3-84 ng/g dw, <2-2000 ng/g dw, <1-170 ng/g dw and <0.03-<0.3 ng/g dw, respectively. Foodstuffs: Certain food products are processed using antifoam containing D4. Bioaccumulation: D3, D4, D5 and D6 have octanol-water partition coefficients of 4.47, 5.1, 5.2 and 6.33 (log value), respectively, which indicate a high potential for bioaccumulation. HMDS has an octanol-water partition coefficient of 4.2 (log value), which indicate a moderate potential for bioaccumulation. For D4 an experimental bioconcentration factor of 12400 was obtained in fathead minnows. This indicates a potential for D4 to bioconcentrate in fish and aquatic organisms, although some reports indicate that this is unlikely in the environment due to Siloxane rapid rate of volatilization to the atmosphere. In Denmark, concentrations of siloxanes in marine fish and mammals have been measured at four locations. For marine fish the concentrations of D4, D5 and D6 were in the range <5-13 ng/g wet weight (ww), <5-52 ng/g ww and <5-8.7 ng/g ww, respectively, and for HMDS the concentrations were <0.4 ng/g ww. For seals the concentrations of D4, D5 and D6 were in the range <5-12 ng/g ww, 17-24 ng/g ww and <5-7.9 ng/g ww, respectively, and for HMDS the concentrations were <0.4 ng/g ww. TemaNord (2005) concluded that siloxanes are present as common pollutants in the Nordic environment and in many different matrices. They seem to be emitted through diffuse pathways and they enter the aquatic food chain. At present, the observed concentrations are not alarmingly high, and background sites seem to be non-contaminated. However, the use of siloxanes is extensive and Siloxane is possible that continued use will lead to increased environmental levels, eventually reaching effect concentrations. Characteristics of Siloxane: Compounds with silicon bound to oxygen, generally with organic groups linked to the silicon atoms, (R3-Si-O-Si-R3 where R is an organic group). Polymerized siloxanes with organic side chains (R - H) are commonly known as silicones or as polysiloxanes. Representative examples are [SiO(CH3)2]n (polydimethylsiloxane) and [SiO(C6H5)2]n (polydiphenylsiloxane). These compounds can be viewed as a hybrid of both organic and inorganic compounds. The organic side chains confer hydrophobic properties while the -Si-O-Si-O- backbone is purely inorganic. Siloxanes can be found in products such as cosmetics, deodorant, defoamers, water repelling windshield coating, lubricants, molded lenses for high-powered LED's, food additives and some soaps. They are being evaluated as environmentally preferable alternatives to perchloroethylene for dry cleaning. Cyclomethicones: Cyclomethicones are a group of methyl siloxanes, a class of liquid silicones (cyclic polydimethylsiloxane polymers) that possess the characteristics of low viscosity and high volatility as well as being skin emollients and in certain circumstances useful cleaning solvents. Unlike dimethicones, which are linear siloxanes that do not evaporate, cyclomethicones are cyclic: both groups consist of a backbone of [(CH3)2SiO]n. They are used in many cosmetic products including deodorants and antiperspirants which need to coat the skin but not remain tacky afterward. Dow is a major producer of cyclomethicones. Cyclomethicones, like all siloxanes, degrade by hydrolysis, producing silanols. These silanols are produced at such low levels that they do not interfere with hydrolytic enzymes. Even though some cyclomethicones structurally resemble crown ethers, they bind metal ions only weakly. Nomenclature of Siloxane: The word siloxane is derived from the words silicon, oxygen, and alkane. In some cases, siloxane materials are composed of several different types of siloxane groups; these are labeled according to the number of Si−O bonds: M-units: (CH3)3SiO0.5, D-units: (CH3)2SiO, T-units: (CH3)SiO1.5. Structure of Siloxane: Siloxanes generally adopt structures expected for linked tetrahedral ("sp3-like") centers. The Si−O bond length is 1.64 Å (vs Si–C distance of 1.92 Å) and the Si-O-Si angle is rather open at 142.5°. By contrast, the C−O distance in a typical dialkyl ether is much shorter at 1.414(2) Å with a more acute C−O−C angle of 111°. Siloxane can be appreciated that the siloxanes would have low barriers for rotation about the Si−O bonds as a consequence of low steric hindrance. This geometric consideration is the basis of the useful properties of some siloxane-containing materials, such as their low glass transition temperatures. Polymers in Biology and Medicine of Siloxane: Siloxane Polymers: Siloxane polymers have been widely used in antimicrobial and nonfouling surfaces, but their use as solution-based antimicrobials is far more limited. Sauvet et al.105 developed a postfunctionalizaton method to create quaternary ammonium-containing siloxane polymers (C14). Homopolymers, as well as random and block copolymers with PDMS, were created by a combination of polycondensation and anionic ring-opening polymerization. To convert the chloropropyl side groups into quaternary ammoniums, the polymer was first treated with lithium bromide to replace the chlorine with bromine. The polymer was dissolved with (3-hydroxypropyl)dimethylamine to create the amphiphilic quaternary amine-functionalized polymer. Bactericidal assays of statistical and block copolymers gave MIC values of 6–25 μg ml−1 against E. coli and S. aureus, with somewhat better activity against S. aureus. A similar class of siloxane polymers was created with imidazolium groups (C15). Monomer synthesis consisted of combining N-allylimidazole and methyldiethoxysilane at elevated temperature.  Homopolymers were created by polycondensation. Polymers with dimethylsiloxane spacers were also created by anionic ring-opening polymerization. Both classes of imidazole polymers were then reacted with n-octyl bromide to create the imidazolium side chains. Bactericidal activities of these polymers were similar to the quaternary ammonium polymers. Synthesis of Siloxane: The main route to siloxane functional group is by hydrolysis of silicon chlorides: 2 R3Si−Cl + H2O → R3Si−O−SiR3 + 2 HCl The reaction proceeds via the initial formation of silanols (R3Si−OH): R3Si−Cl + H2O → R3Si−OH + HCl The siloxane bond can then form via a silanol + silanol pathway or a silanol + chlorosilane pathway: 2 R3Si−OH → R3Si−O−SiR3 + H2O R3Si−OH + R3Si−Cl → R3Si−O−SiR3 + HCl Hydrolysis of a silyldichloride can afford linear or cyclic products. Linear products are terminated with silanol groups: n R2Si(OH)2 → H(R2SiO)nOH + (n − 1) H2O Cyclic products have no silanol termini: n R2Si(OH)2 → (R2SiO)n + n H2O The linear products, polydimethylsiloxane (PDMS), are of great commercial value. Their production requires the production of dimethylsilicon dichloride. Starting from trisilanols, cages are possible, such as the species with the formula (RSi)nO3n/2 with cubic (n = 8) and hexagonal prismatic (n = 12) structures. The cubic cages are cubane-type clusters, with silicon centers at the corners of a cube oxygen centres spanning each of the twelve edges. Reactions of Siloxane: Oxidation of organosilicon compounds, including siloxanes, gives silicon dioxide. This conversion is illustrated by the combustion of hexamethylcyclotrisiloxane: ((CH3)2SiO)3 + 12 O2 → 3 SiO2 + 6 CO2 + 9 H2O Strong base degrades siloxane group, often affording siloxide salts: ((CH3)3Si)2O + 2 NaOH → 2 (CH3)3SiONa + H2O This reaction proceeds by production of silanols. Similar reactions are used industrially to convert cyclic siloxanes to linear polymers. Safety and environmental considerations of Siloxane: Because silicones are heavily used in biomedical and cosmetic applications, their toxicology has been intensively examined. "The inertness of silicones toward warmblooded animals has been demonstrated in a number of tests." With an LD50 in rats of >50 g/kg, they are virtually nontoxic.

Questions remain however about chronic toxicity or the consequences of bioaccumulation since siloxanes can be long-lived.

Findings about bioaccumulation have been largely based on laboratory studies.

Field studies of bioaccumulation have not reached consensus.

“Even if the concentrations of siloxanes we have found in fish are high compared to concentrations of classical contaminants like PCBs, several other studies in the Oslo Fjord in Norway, Lake Pepin in the US, and Lake Erie in Canada have shown concentrations of siloxanes decrease at higher range in the food chain.

This finding raises questions about which factors influence the bioaccumulation potential of siloxanes.”

Cyclomethicones are ubiquitous because they are widely used in biomedical and cosmetic applications.

They can be found at high levels in American cities.

They can be toxic to aquatic animals in concentrations often found in the environment.

The cyclomethicones D4 and D5 are bioaccumulative in some aquatic organisms, according to one report.

In the European Union, D4, D5 and D6 have been deemed hazardous as per the REACH regulation.

They were characterized as substances of very high concern (SVHC) due to their PBT and vPvB properties.

Canada regulates D4 under a pollution prevention plan.

A scientific review in Canada in 2011 concluded that “Siloxane D5 does not pose a danger to the environment.”

Handling and Storage of Siloxane:

Precautions for safe handling:

Advice on safe handling:

Ensure adequate ventilation, especially in confined areas.

Keep away fromheat, sparks, flame and other sources of ignition (i.e., pilot lights, electric motors and static electricity).

Take precautionary measures against static discharges.

Use spark-proof tools andexplosion-proof equipment.

All equipment used when handling Siloxane must begrounded.

Use with local exhaust ventilation.

Use personal protective equipment asrequired.

Do not breathe dust/fume/gas/mist/vapors/spray.

Conditions for safe storage, including any incompatibilities:

Storage Conditions Keep in a dry, cool and well-ventilated place.

Keep in properly labeled containers.

Keep out of the reach of children.

Incompatible materials:

Acids.

Bases.

Strong oxidizing agents.

Metals.

Amines.

Stability and Reactivity of Siloxane:

Chemical stability:

Stable under recommended storage conditions.

Possibility of hazardous reactions:

None under normal processing.

Conditions to avoid

Heat, flames and sparks.

Incompatible materials:

Acids.

Bases.

Strong oxidizing agents.

Metals.

Amines.

Hazardous decomposition products:

silicon dioxide.

Carbon oxides.

Hydrocarbons.

First Aid Measures of Siloxane:

General advice:

Immediate medical attention is required.

In case of accident or unwellness, seekmedical advice immediately (show directions for use or safety data sheet if possible).

If symptoms persist, call a physician.

Eye contact:

Immediately flush with plenty of water.

After initial flushing, remove any contact lensesand continue flushing for at least 15 minutes.

Keep eye wide open while rinsing.

If symptoms persist, call a physician.

Skin Contact:

Wash off immediately with plenty of water.

Wash contaminated clothing beforereuse.

If skin irritation persists, call a physician.

Inhalation:

Remove to fresh air.

If breathing is irregular or stopped, administer artificial respiration.

Avoid direct contact with skin.

Use barrier to give mouth-to-mouth resuscitation.

Call aphysician.

Ingestion:

Do NOT induce vomiting.

Rinse mouth.

Drink plenty of water.

Never give anything by mouth to an unconscious person.

Call a physician.

Self-protection of the first aider Remove all sources of ignition.

Use personal protective equipment as required.

Most important symptoms and effects, both acute and delayed:

Symptoms Harmful if inhaled.

Causes serious eye irritation.

Causes skin irritation.

Respiratoryirritation.

Indication of any immediate medical attention and special treatment needed:

Note to physicians Treat symptomatically.

Fire-fighting Measures of Siloxane:

Suitable Extinguishing Media:

Carbon dioxide (CO2).

Water spray (fog).

Alcohol resistant foam.

Unsuitable Extinguishing Media Caution:

Use of water spray when fighting fire may be inefficient.

Do not use asolidwaterstream as Siloxane may scatter and spread fire.

Specific hazards arising from the chemical:

No information available.

Protective equipment and precautions for firefighters:

Wear self contained breathing apparatus for fire fighting if necessary.

Accidental Release Measures of Siloxane:

Personal precautions, protective equipment and emergency procedures:

Personal precautions Remove all sources of ignition.

Pay attention to flashback.

Evacuate personnel tosafeareas.

Ensure adequate ventilation, especially in confined areas.

Use personal protectiveequipment as required.

Keep people away from and upwind of spill/leak.

Environmental precautions:

Environmental precautions Prevent further leakage or spillage if safe to do so.

Prevent product fromenteringdrains.

Donot flush into surface water or sanitary sewer system.

Methods and material for containment and cleaning up:

Methods for containment Prevent further leakage or spillage if safe to do so.

Dike far ahead of liquid spill for laterdisposal.

Methods for cleaning up Use personal protective equipment as required.

Cover liquid spill withsand, earthor other non-combustible absorbent material.

Pick up and transfer to properly labeledcontainers.

Use clean non-sparking tools to collect absorbed material.

Take precautionarymeasures against static discharges.

Ground and bond containers when transferring material.

Identifiers of Siloxane:

CAS Number: 63148-62-9

EC  Number: 205-492-2

Molecular Formula: C8H24O2Si3

Molecular Weight: 236.53

Names of Siloxane:

Regulatory process names:

Siloxanes and Silicones, 3-[3-(acetyloxy)-2-hydroxypropoxy]propyl Me, di-Me, 3-[2-hydroxy-3-[(1-oxo-2-propen-1-yl)oxy]propoxy]propyl Me

IUPAC names:

Acrylated polysiloxanes

Siloxanes and Silicones, 3-[3-(acetyloxy)-2-hydroxypropoxy]propyl Me, di-Me, 3-[2-hydroxy-3-[(1-oxo-2-propen-1-yl)oxy]propoxy]propyl

Siloxanes and Silicones, 3-[3-(acetyloxy)-2-hydroxypropoxy]propyl Me, di-Me, 3-[2-hydroxy-3-[(1-oxo-2-propen-1-yl)oxy]propoxy]propyl Me

Siloxanes and Silicones, 3-[3-(acetyloxy)-2-hydroxypropoxy]propyl Me, di-Me, 3-[2-hydroxy-3-[(1-oxo-2-propenyl)oxy]propoxy]propy

Siloxanes and Silicones, 3-[3-(acetyloxy)-2-hydroxypropoxy]propyl Me, di-Me, 3-[2-hydroxy-3-[(1-oxo-2-propenyl)oxy]propoxy]propyl Me

Siloxanes and Silicones, 3-[3-(acetyloxy)-2-hydroxypropoxy]propyl Me, di-Me, 3-[2-hydroxy-3-[(1-oxo-2-propenyl)oxy]propoxy]propyl Me (AICS

Other name:

Siloxanes and Silicones, di-Me,3-{[2-Hydroxy-3((1-oxo-2- propenyl)oxy)propyl]oxy}propyl Me, 3-{[2-hydroxy-3-3(acetoxy)propyl]oxy}

Other identifiers:

125455-51-8