POLYDIMETHYLSILOXANE

CAS Number : 63148-62-9
EC  Number : 613-156-5
Chemical formula :  CH3[Si(CH3)2O]nSi(CH3)3
Density        :  0.965 g/cm3

IUPAC name : 
-poly(dimethylsiloxane)

Other names : 
-PDMS
-dimethicone
-dimethylpolysiloxane
-E900

Polydimethylsiloxane, also known as dimethylpolysiloxane or dimethicone, belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones and siloxane. Polydimethylsiloxane is the most widely used silicon-based organic polymer, as its versatility and properties lead to many applications.
Polydimethylsiloxane is particularly known for its unusual rheological (or flow) properties. 
Polydimethylsiloxane is optically clear and, in general, inert, non-toxic, and non-flammable. 
Polydimethylsiloxane is one of several types of silicone oil (polymerized siloxane). 
Its applications range from contact lenses and medical devices to elastomers; it is also present in shampoos (as it makes hair shiny and slippery), food (antifoaming agent), caulk, lubricants and heat-resistant tiles.

Structure of Polydimethylsiloxane
The chemical formula of Polydimethylsiloxane is CH3[Si(CH3)2O]nSi(CH3)3, where n is the number of repeating monomer [Si(CH3)2O] units.
Industrial synthesis can begin from dimethyldichlorosilane and water by the following net reaction:

n Si(CH3)2Cl2 + (n + 1) H2O → HO[−Si(CH3)2O−]nH + 2n HCl

The polymerization reaction evolves hydrochloric acid. 
For medical and domestic applications, a process was developed in which the chlorine atoms in the silane precursor were replaced with acetate groups. 
In this case, the polymerization produces acetic acid, which is less chemically aggressive than HCl. 
As a side-effect, the curing process is also much slower in this case. 
The acetate is used in consumer applications, such as silicone caulk and adhesives.

Branching and capping
Hydrolysis of Si(CH3)2Cl2 generates a polymer that is terminated with silanol groups (–Si(CH3)2OH). 
These reactive centers are typically "capped" by reaction with trimethylsilyl chloride:

2 Si(CH3)3Cl + [Si(CH3)2O]n-2[Si(CH3)2OH]2 → [Si(CH3)2O]n-2[Si(CH3)2OSi(CH3)3]2 + 2 HCl

Silane precursors with more acid-forming groups and fewer methyl groups, such as methyltrichlorosilane, can be used to introduce branches or cross-links in the polymer chain. 
Under ideal conditions, each molecule of such a compound becomes a branch point. 
Polydimethylsiloxane can be used to produce hard silicone resins. 
In a similar manner, 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.

Well-defined Polydimethylsiloxane with a low polydispersity index and high homogeneity is produced by controlled anionic ring-opening polymerization of hexamethylcyclotrisiloxane. 
Using this methodology it is possible to synthesize linear block copolymers, heteroarm star-shaped block copolymers and many other macromolecular architectures.

The polymer is manufactured in multiple viscosities, from a thin pourable liquid (when n is very low), to a thick rubbery semi-solid (when n is very high). 
Polydimethylsiloxane molecules have quite flexible polymer backbones (or chains) due to their siloxane linkages, which are analogous to the ether linkages used to impart rubberiness to polyurethanes. 
Such flexible chains become loosely entangled when molecular weight is high, which results in Polydimethylsiloxane' unusually high level of viscoelasticity.

Mechanical properties of Polydimethylsiloxane
Polydimethylsiloxane is viscoelastic, meaning that at long flow times (or high temperatures), it acts like a viscous liquid, similar to honey. 
However, at short flow times (or low temperatures), it acts like an elastic solid, similar to rubber. 
Viscoelasticity is a form of nonlinear elasticity that is common amongst noncrystalline polymers.
The loading and unloading of a stress-strain curve for Polydimethylsiloxane do not coincide; rather, the amount of stress will vary based on the degree of strain, and the general rule is that increasing strain will result in greater stiffness. 

When the load itself is removed, the strain is slowly recovered (rather than instantaneously). 
This time-dependent elastic deformation results from the long-chains of the polymer. 
But the process that is described above is only relevant when cross-linking is present; when it is not, the polymer Polydimethylsiloxane cannot shift back to the original state even when the load is removed, resulting in a permanent deformation. 
However, permanent deformation is rarely seen in Polydimethylsiloxane, since it is almost always cured with a cross-linking agent.

If some Polydimethylsiloxane is left on a surface overnight (long flow time), it will flow to cover the surface and mold to any surface imperfections. 
However, if the same PDMS is poured into a spherical mold and allowed to cure (short flow time), it will bounce like a rubber ball.
The mechanical properties of Polydimethylsiloxane enable this polymer to conform to a diverse variety of surfaces. 
Since these properties are affected by a variety of factors, this unique polymer is relatively easy to tune.
This enables Polydimethylsiloxane to become a good substrate that can easily be integrated into a variety of microfluidic and microelectromechanical systems.

Specifically, the determination of mechanical properties can be decided before Polydimethylsiloxane is cured; the uncured version allows the user to capitalize on myriad opportunities for achieving a desirable elastomer. 
Generally, the cross-linked cured version of Polydimethylsiloxane resembles rubber in a solidified form. 
Polydimethylsiloxane is widely known to be easily stretched, bent, compressed in all directions.
Depending on the application and field, the user is able to tune the properties based on what is demanded.

Overall Polydimethylsiloxane has a low elastic modulus which enables it to be easily deformed and results in the behavior of a rubber.
Viscoelastic properties of Polydimethylsiloxane can be more precisely measured using dynamic mechanical analysis. 
This method requires determination of the material's flow characteristics over a wide range of temperatures, flow rates, and deformations. 
Because of Polydimethylsiloxane's chemical stability, it is often used as a calibration fluid for this type of experiment.
The shear modulus of Polydimethylsiloxane varies with preparation conditions, and consequently dramatically varies in the range of 100 kPa to 3 MPa. 
The loss tangent is very low (tan δ ≪ 0.001).

Chemical compatibility of Polydimethylsiloxane
Polydimethylsiloxane is hydrophobic.
Plasma oxidation can be used to alter the surface chemistry, adding silanol (SiOH) groups to the surface. 
Atmospheric air plasma and argon plasma will work for this application. 
This treatment renders the Polydimethylsiloxane surface hydrophilic, allowing water to wet it. 

The oxidized surface can be further functionalized by reaction with trichlorosilanes. 
After a certain amount of time, recovery of the surface's hydrophobicity is inevitable, regardless of whether the surrounding medium is vacuum, air, or water; the oxidized surface is stable in air for about 30 minutes.
Alternatively, for applications where long-term hydrophilicity is a requirement, techniques such as hydrophilic polymer grafting, surface nanostructuring, and dynamic surface modification with embedded surfactants can be of use.

Solid Polydimethylsiloxane samples (whether surface-oxidized or not) will not allow aqueous solvents to infiltrate and swell the material. 
Thus Polydimethylsiloxane structures can be used in combination with water and alcohol solvents without material deformation. 
However most organic solvents will diffuse into the material and cause it to swell.
Despite this, some organic solvents lead to sufficiently small swelling that they can be used with Polydimethylsiloxane, for instance within the channels of Polydimethylsiloxane microfluidic devices. 

The swelling ratio is roughly inversely related to the solubility parameter of the solvent. 
Diisopropylamine swells Polydimethylsiloxane to the greatest extent; solvents such as chloroform, ether, and THF swell the material to a large extent. 
Solvents such as acetone, 1-propanol, and pyridine swell the material to a small extent. 
Alcohols and polar solvents such as methanol, glycerol and water do not swell the material appreciably.

Applications of Polydimethylsiloxane

Surfactants and antifoaming agents
Polydimethylsiloxane is a common surfactant and is a component of defoamers.
Polydimethylsiloxane, in a modified form, is used as an herbicide penetrant  and is a critical ingredient in water-repelling coatings, such as Rain-X.

Hydraulic fluids and related applications
Polydimethylsiloxane is used in the active silicone fluid in automotive viscous limited slip differentials and couplings.

Daytime radiative cooling
Polydimethylsiloxane is a common surface material used in passive daytime radiative cooling as a broadband emitter that is high in solar reflectivity and heat emissivity. 
Many tested surfaces use Polydimethylsiloxane because of its potential scalability as a low-cost polymer.
As a daytime radiative cooling surface, Polydimethylsiloxane has also been tested to improve solar cell efficiency.

Soft lithography
Polydimethylsiloxane is commonly used as a stamp resin in the procedure of soft lithography, making it one of the most common materials used for flow delivery in microfluidics chips.
The process of soft lithography consists of creating an elastic stamp, which enables the transfer of patterns of only a few nanometers in size onto glass, silicon or polymer surfaces. 
With this type of technique, it is possible to produce devices that can be used in the areas of optic telecommunications or biomedical research. 
The stamp is produced from the normal techniques of photolithography or electron-beam lithography. 
The resolution depends on the mask used and can reach 6 nm.

The popularity of Polydimethylsiloxane in microfluidics area is due to its excellent mechanical properties. 
Moreover, compared to other materials, it possesses superior optical properties, allowing for minimal background and autofluorescence during for fluorescent imaging.
In biomedical (or biological) microelectromechanical systems (bio-MEMS), soft lithography is used extensively for microfluidics in both organic and inorganic contexts. 
Silicon wafers are used to design channels, and Polydimethylsiloxane is then poured over these wafers and left to harden. 

When removed, even the smallest of details is left imprinted in the Polydimethylsiloxane. 
With this particular Polydimethylsiloxane block, hydrophilic surface modification is conducted using plasma etching techniques. 
Plasma treatment disrupts surface silicon-oxygen bonds, and a plasma-treated glass slide is usually placed on the activated side of the Polydimethylsiloxane (the plasma-treated, now hydrophilic side with imprints). 

Once activation wears off and bonds begin to reform, silicon-oxygen bonds are formed between the surface atoms of the glass and the surface atoms of the Polydimethylsiloxane, and the slide becomes permanently sealed to the Polydimethylsiloxane, thus creating a waterproof channel. 
With these devices, researchers can utilize various surface chemistry techniques for different functions creating unique lab-on-a-chip devices for rapid parallel testing.
Polydimethylsiloxane can be cross-linked into networks and is a commonly used system for studying the elasticity of polymer networks.
Polydimethylsiloxane can be directly patterned by surface-charge lithography.

Polydimethylsiloxane is being used in the making of synthetic gecko adhesion dry adhesive materials, to date only in laboratory test quantities.
Some flexible electronics researchers use Polydimethylsiloxane because of its low cost, easy fabrication, flexibility, and optical transparency.
Yet, for fluorescence imaging at different wavelengths, Polydimethylsiloxane shows least autofluorescence and is comparable to BoroFloat glass.

Medicine and cosmetics
Activated dimethicone, a mixture of polydimethylsiloxanes and silicon dioxide (sometimes called simethicone), is often used in over-the-counter drugs as an antifoaming agent and carminative.
Polydimethylsiloxane also works as a moisturizer that is lighter and more breathable than typical oils.
Silicone breast implants are made out of a Polydimethylsiloxane elastomer shell, to which fumed amorphous silica is added, encasing PDMS gel or saline solution.
The use of Polydimethylsiloxane in the manufacture of contact lenses was patented (later abandoned).

Skin
Polydimethylsiloxane is used variously in the cosmetic and consumer product industry as well. 
For example, dimethicone is used widely in skin-moisturizing lotions where it is listed as an active ingredient whose purpose is "skin protection." 
Some cosmetic formulations use dimethicone and related siloxane polymers in concentrations of use up to 15%. 
The Cosmetic Ingredient Review's (CIR) Expert Panel, has concluded that dimethicone and related polymers are "safe as used in cosmetic formulations."

Hair
Polydimethylsiloxane compounds such as amodimethicone, are effective conditioners when formulated to consist of small particles and be soluble in water or alcohol/act as surfactants (especially for damaged hair), and are even more conditioning to the hair than common dimethicone and/or dimethicone copolyols.

Contact lenses
A proposed use of Polydimethylsiloxane is contact lens cleaning. 
Its physical properties of low elastic modulus and hydrophobicity have been used to clean micro and nano pollutants from contact lens surfaces more effectively than multipurpose solution and finger rubbing; the researchers involved call the technique PoPPR (polymer on polymer pollution removal) and note that it is highly effective at removing nanoplastic that has adhered to lenses.

As anti-parasitic
Polydimethylsiloxane is effective for treating lice in humans. 
This is thought to be due not to suffocation (or poisoning), but to its blocking water excretion, which causes insects to die from physiological stress either through prolonged immobilisation or disruption of internal organs such as the gut.

Polydimethylsiloxane is the active ingredient in an anti-flea preparation sprayed on a cat, found to be equally effective to a widely used more toxic pyriproxifen/permethrin spray. 
The parasite becomes trapped and immobilised in the substance, inhibiting adult flea emergence for over three weeks.

Foods
Polydimethylsiloxane is added to many cooking oils (as an anti-foaming agent) to prevent oil splatter during the cooking process. 
As a result of this, Polydimethylsiloxane can be found in trace quantities in many fast food items such as McDonald's Chicken McNuggets, French fries, hash browns, milkshakes and smoothies and Wendy's French fries.
Under European food additive regulations, it is listed as E900.

Condom lubricant
Polydimethylsiloxane is widely used as a condom lubricant.

Domestic and niche uses
Many people are indirectly familiar with Polydimethylsiloxane because it is an important component in Silly Putty, to which Polydimethylsiloxane imparts its characteristic viscoelastic properties.
Another toy Polydimethylsiloxane is used in is Kinetic Sand. 
The rubbery, vinegary-smelling silicone caulks, adhesives, and aquarium sealants are also well-known.
Polydimethylsiloxane is also used as a component in silicone grease and other silicone based lubricants, as well as in defoaming agents, mold release agents, damping fluids, heat transfer fluids, polishes, cosmetics, hair conditioners and other applications.
Polydimethylsiloxane can be used as a sorbent for the analysis of headspace (dissolved gas analysis) of food.

Polydimethylsiloxane  is the simplest member of the silicone polymer family. 
Polydimethylsiloxane is formed by hydrolyzing Me2SiCl2, which is produced from high-purity SiO2 and CH2Cl2 by the Muller–Rochow reaction. 
The term “silicone” was coined by chemist F. S. Kipping in 1901.
Low–molecular weight PDMS is a liquid used in lubricants, antifoaming agents, and hydraulic fluids. Its use in breast implants is not as popular as it once was because of safety concerns.

At higher molecular weights, Polydimethylsiloxane is a soft, compliant rubber or resin. 
Polydimethylsiloxane is used in caulks, sealants, an even Silly Putty. 
More recently, Polydimethylsiloxane resins have been used in soft lithography, a key process in biomedical microelectromechanical systems . 

Polydimethylsiloxane has several useful material properties for stamping and molding. 
Polydimethylsiloxane provides a surface that has a low interfacial free energy, is chemically inert, has good gas permeability and good thermal stability, and is optically transparent. 
The surface properties of Polydimethylsiloxane are also relatively easy to modify. 

Polydimethylsiloxane  is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological (or flow) properties. 
Its applications range from contact lenses and medical devices to elastomers, caulking, lubricating oils and heat resistant tiles.
Polydimethylsiloxane is optically clear, and is generally considered to be inert, non-toxic and non-flammable. 
Polydimethylsiloxane has been assigned CAS number 63148-62-9, and is occasionally called dimethicone. 
Polydimethylsiloxane is one of several types of silicone oil (polymerized siloxane).

Chemistry of Polydimethylsiloxane
The chemical formula for PDMS is (H3C)3[Si(CH3)2O]nSi(CH3)3, where n is the number of repeating monomer [SiO(CH3)2] units. 
Industrial synthesis can begin from dimethylchlorosilane and water by the following net reaction:

n [Si(CH3)2Cl2] + n [H2O] → [Si(CH3)2O]n + 2n HCl

During polymerization, this reaction evolves potentially hazardous hydrogen chloride gas. 
For medical uses, a process was developed where the chlorine atoms in the silane precursor were replaced with acetate groups, so that the reaction product of the final curing process is nontoxic acetic acid (vinegar). 
As a side effect, the curing process is also much slower in this case. 
This is the chemistry used in consumer applications, such as silicone caulk and adhesives.

Silane precursors with more acid-forming groups and fewer methyl groups, such as methyltrichlorosilane, can be used to introduce branches or cross-links in the polymer chain. 
Ideally, each molecule of such a compound becomes a branch point. 
This 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.

The polymer is manufactured in multiple viscosities, ranging from a thin pourable liquid (when n is very low), to a thick rubbery semi-solid (when n is very high). 
Polydimethylsiloxane molecules have quite flexible polymer backbones (or chains) due to their siloxane linkages, which are analogous to the ether linkages used to impart rubberiness to polyurethanes. 
Such flexible chains become loosely entangled when molecular weight is high, which results in Polydimethylsiloxane having an unusually high level of viscoelasticity.

Polydimethylsiloxane  belongs to a group of polymeric organosilicon compounds that are referred to as silicones and is the most widely used silicon-based organic-polymer. Polydimethylsiloxane  is particularly known for its unusual rheological or flow properties. 
Polydimethylsiloxane is optically clear and inert, non-toxic, and non-flammable. 
Polydimethylsiloxane is one of several types of silicone oil (polymerized siloxane). 

Applications of Polydimethylsiloxane

-Component of defoamers
-Ingredient in water-repellent coatings
-Plasticizer in silicone sealants
-Stamp resin in the procedure of soft-lithography
-Lubricant in condoms
-A component in silicone grease
-A component in heat-transfer fluids
-A component in mold-release agents
-Sorbent for the analysis of head-space

Polydimethylsiloxane, called PDMS or dimethicone, is a polymer widely used for the fabrication and prototyping of microfluidic chips.
Polydimethylsiloxane is a mineral-organic polymer (a structure containing carbon and silicon) of the siloxane family (word derived from silicon, oxygen and alkane). 
Apart from microfluidics, it is used as a food additive (E900), in shampoos, and as an anti-foaming agent in beverages or in lubricating oils.
For the fabrication of microfluidic devices, Polydimethylsiloxane (liquid) mixed with a cross-linking agent is poured into a microstructured mold and heated to obtain a elastomeric replica of the mold.

PHYSICAL AND CHEMICAL PROPERTIES of Polydimethylsiloxane
BOILING POINT (°C) : >200 °C; 392 °F; Polymer
VAPOR PRESSURE (20 C) (MM HG) : 1
VAPOR DENSITY (AIR=1) : > 1.0
FREEZING POINT: < -25 °C ; -13 °F
PHYSICAL STATE : Liquid
ODOR : Odorless
Color : Colorless

FIRST AID MEASURES of Polydimethylsiloxane

INGESTION :
If swallowed, do NOT induce vomiting. 
Give a glass of water. 
Seek medical advice. 
Never give liquid to an unconscious person.

SKIN : 
Wash area with soap and water.

INHALATION :
If inhaled, remove to fresh air. 
If not breathing give artificial respiration using a barrier device. 
If breathing is difficult give oxygen. 
Get medical attention.

EYES : 
Rinse immediately with plenty of water. 
Consult a physician for specific advice.

Substance identity

EC / List no.: 613-156-5
CAS no.: 63148-62-9

Hazard classification & labelling of Polydimethylsiloxane
Warning! According to the classification provided by companies to ECHA in CLP notifications this substance causes serious eye irritation.

Polydimethylsiloxane indicated, in 2009, as being intended to be registered by at least one company in the EEA.
Polydimethylsiloxane for which classification and labeling data have been submitted to ECHA in a registration under REACH or notified by manufacturers or importers under CLP. 
Such notifications are required for hazardous substances, as such or in mixtures, as well as for all substances subject to registration, regardless of their hazard.

Synonyms:
polydimethylsiloxane (Mw > 6800 Da)
Polydimethylsiloxanes
Siloxanes and Silicones, di-Me
Baysilon
Dimethicone
DiMethyl Polysiloxane
dimethyl polysiloxane
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
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
83047-13-6
9049-10-9
9076-36-2