About this family
A siloxane chain is not a carbon backbone at all. Alternating silicon and oxygen atoms, –[Si(R2)–O]–, give the family a set of properties no organic polymer matches, and the reasons are all geometric. The Si–O bond is longer than C–C (about 1.64 Å against 1.54 Å), the Si–O–Si angle is far wider than a tetrahedral carbon's (roughly 140° against 109.5°), and the barrier to rotation about the bond is close to nothing. The chain is exceptionally limber.
Poly(dimethylsiloxane) shows what that buys. Its glass transition is −125 °C – the lowest of any polymer in ordinary use – so it stays rubbery through the whole range a terrestrial application will ever see. Its gas permeability is the highest of the common polymers, which is why it turns up as a membrane material and in oxygen-permeable contact lenses. Its surface energy is very low, which is what makes it a release coating, an antifoam, and a mould-making rubber. And the Si–O bond is strong enough that the family tolerates heat and oxidation that would degrade a hydrocarbon.
What sets the properties
Most siloxanes are made by ring-opening the cyclic oligomers rather than by condensing silanols: the tetramer D4 and trimer D3 are opened under acid or base catalysis. The distinction matters in practice. Anionic ring-opening of the strained trimer can be run as a living polymerisation and gives a defined molecular weight and narrow distribution; equilibration of the unstrained tetramer instead settles into a thermodynamic mixture of chains and rings, giving a broad product that always contains residual cyclics.
The two substituents on each silicon are where the family diversifies. Replacing methyl with phenyl stiffens the chain, raises the refractive index, and improves radiation resistance. A trifluoropropyl group buys resistance to fuels and hydrocarbon oils that a dimethyl silicone swells in badly. Hydride and vinyl substituents are reactive handles rather than property modifiers: a hydride on silicon adds across a vinyl on another chain under a platinum catalyst, and that hydrosilylation is the addition cure behind most two-part silicone rubbers. Aminopropyl, epoxy and polyether substituents make the chain compatible with organic resins or with water, which is how silicone surfactants and copolymer coatings are built.
All 87 in the library
Sorted by parent name, ignoring the leading "poly" and any locants – so poly(2-hydroxyethyl methacrylate) files under H. 87 of the 87 carry a note, and every one is searchable by drawn structure on the structure search page. 2 have a CAS registry number for the polymer; most specialty polymers have never been assigned one, and the number you find in a catalogue is usually the monomer's, which is why the field is blank rather than borrowed here.
A
Poly(acryloxypropylmethylsiloxane)
The acrylate analogue, appreciably faster under UV than the methacrylate and correspondingly more prone to premature gelation in storage.
Poly(N-(2-aminoethyl)aminopropylmethylsiloxane)
The diamine-functional fluid. The secondary amine next to a primary one chelates and adsorbs far more strongly than a plain aminopropyl group, at the cost of yellowing on heat ageing.
Poly(aminopropylmethylsiloxane)
The amine-functional silicone fluid. Pendant primary amines give it substantivity to hair, textiles and cellulose - the chemistry behind almost every silicone fabric and hair conditioner - and a site for cure with epoxies and isocyanates.
Poly(azidopropylmethylsiloxane)
A clickable silicone. The pendant azide survives the cationic ring-opening used to make it and then couples to alkynes, which is how silicones are joined to blocks that will not tolerate hydrosilylation catalysts.
B
Poly(butylvinylsiloxane)
A vinyl-functional fluid whose butyl co-substituent gives the cured elastomer better swelling resistance in hydrocarbons than a methylvinyl network.
C
Poly(carborane siloxane)
An icosahedral boron cage spliced into a silicone chain, giving a rubber that survives above 400 C in air where ordinary silicone unzips at 300. The cage is aromatic in three dimensions and essentially inert, and it blocks the backbiting depolymerisation that normally destroys a siloxane. Undrawn: the twelve-vertex closo cage is not a structure a flat bond list represents honestly.
Polycarbosilane
A polymer made to be destroyed. Alternating silicon and carbon in the backbone means that pyrolysis leaves silicon carbide behind in the shape the polymer was formed in, so a ceramic fibre can be spun as a plastic and then fired - which is how continuous SiC fibre for turbine composites is made at all, ceramics being unspinnable. Obtained by rearranging polydimethylsilane, which has no carbon in its backbone, under heat.
Poly(carboxypropylmethylsiloxane)
A carboxy-functional silicone fluid, used where an anionic or salt-forming group is needed on an otherwise strongly hydrophobic chain.
Poly(chloropropylmethylsiloxane)
A precursor fluid rather than an end product: the pendant chloride is displaced by amines, azide or thiolate to reach functional silicones that cannot survive the polymerisation directly.
Poly(cyanoethylmethylsiloxane)
A shorter-tether relative of the cyanopropyl fluid. The nitrile raises the dielectric constant sharply, which is what these polar silicones are used for.
Poly(cyanopropylmethylsiloxane)
A silicone made deliberately polar, the nitrile raising the phase's affinity for polar analytes far above that of the dimethyl fluid. It is a gas chromatography stationary phase rather than a material: the whole point is that retention now depends on a solute's dipole rather than only on its volatility.
D
Poly(diallylsiloxane)
Two allyl groups per silicon. The extra methylene relative to a vinyl makes the addition slower but leaves the silicon-carbon bond further from the crosslink, which reduces strain in the cured network.
Poly(dibenzylsiloxane)
Two benzyl groups per silicon. The methylene spacers let both rings rotate, so the polymer reaches a high refractive index without the chain stiffness of poly(diphenylsiloxane).
Poly(dibutylsiloxane)
A symmetric dialkylsiloxane. Members of this series from dipropyl upwards form columnar mesophases between their glass transition and melting point - liquid crystallinity from side chains alone.
Poly(dicyclohexylsiloxane)
Two rings on every silicon give one of the highest glass transitions in the siloxane family - the backbone is still Si-O, but almost none of its flexibility survives.
Poly(dicyclopentylsiloxane)
Two cycloaliphatic rings on every silicon; a rigid, transparent silicone with no aromatic absorbance, which matters where short-wavelength light would degrade a phenyl siloxane.
Poly(didecylsiloxane)
The C10 symmetric dialkylsiloxane, at the upper end of the series that still forms a mesophase rather than an ordinary side-chain crystal.
Poly(didodecylsiloxane)
The C12 symmetric dialkylsiloxane, a waxy solid in which almost the whole mass of the polymer is side chain.
Poly(diethylsiloxane)
Two carbons per side group instead of one, and the polymer stops behaving like a silicone: it forms a mesophase between its melting and clearing points, a rare case of a flexible chain with no rigid unit forming a liquid crystal. The order comes from the side chains packing, not from the backbone, which is why it disappears again in the propyl homologue.
Poly(diheptylsiloxane)
The C7 symmetric dialkylsiloxane. Both substituents order together, giving a wider mesophase window than the asymmetric alkylmethyl fluids ever show.
Poly(dihexylsiloxane)
One of the dialkylsiloxane mesophase formers; the hexyl chains pack into a two-dimensional lattice while the backbone stays disordered.
Poly(dimethylsiloxane)
Crystallizes only well below room temperature, so its melting point (Odian's Table 1-3) is far sub-ambient.
Poly(dinonylsiloxane)
At C9 the side-chain crystal begins to displace the mesophase, and the material behaves more like a tethered paraffin than a silicone.
Poly(dioctylsiloxane)
The longer symmetric dialkylsiloxane, where side-chain crystallisation begins to override the mesophase.
Poly(dipentylsiloxane)
A symmetric dialkylsiloxane in the range that forms a columnar mesophase; the transition temperatures rise steadily with alkyl length across the series.
Poly(diphenylsiloxane)
The rigid extreme of the siloxane family. Two phenyls per silicon make the chain stiff and highly crystalline, so unlike PDMS it is a solid that melts above 250 C rather than an oil. Used almost entirely as a comonomer, where a small fraction raises the thermal stability and refractive index of an otherwise dimethyl silicone.
Poly(dipropylsiloxane)
Symmetrically substituted like PDMS but with three-carbon groups, which is enough to shift the mesophase behaviour that the dialkylsiloxanes are studied for.
Poly(divinylsiloxane)
Two vinyl groups per silicon makes every repeat unit a crosslink site, so this is a curing resin rather than a fluid.
E
Poly(ethylhydrosiloxane)
A hydride crosslinker with an ethyl co-substituent, used where the cured network has to remain compatible with hydrocarbon media.
Poly(ethylphenylsiloxane)
An aryl silicone with an ethyl rather than a methyl co-substituent, which lowers the melting point of the fluid while keeping the refractive index of the phenyl group.
Poly(ethylvinylsiloxane)
A vinyl-functional fluid with an ethyl rather than a methyl co-substituent, used where the cured network has to stay soluble in hydrocarbons.
F
Poly(ferrocenyldimethylsilane)
Iron built into the main chain, made by ring-opening a strained ferrocenophane. Two things follow: it is redox-active along its length, and it is the block that made crystallisation-driven self-assembly possible - its crystalline core lets block copolymer micelles grow into fibres of precisely controlled length, seeded like a living polymerisation. It also pyrolyses to magnetic ceramic. Not drawn: iron is outside the element set.
G
Poly(glycidoxypropylmethylsiloxane)
An epoxy-functional silicone fluid, cured cationically or with amines. Used to toughen epoxy resins, where the silicone phase-separates into rubbery domains that arrest cracks.
H
Polyhedral oligomeric silsesquioxane
A silica cage a nanometre across with organic groups on every corner, so it behaves as a soluble, precisely defined nanoparticle rather than as a filler - every one is identical, which no ground mineral can claim. Copolymerised into a chain it raises the glass transition and the decomposition temperature at a few percent loading. Undrawn: a closed cage, not a repeat unit.
Poly(hexylvinylsiloxane)
The longer-alkyl vinyl fluid, used where the network has to be built in an oil-rich formulation.
Poly(hydroxypropylmethylsiloxane)
A carbinol-functional silicone. The pendant primary hydroxyls react with isocyanates, which is how silicone segments are built into polyurethane coatings and foams.
M
Poly(mercaptopropylmethylsiloxane)
A thiol-functional silicone. The pendant SH adds across vinyl groups under UV in a thiol-ene cure and binds gold and other soft metals, which puts it in both adhesives and particle surface chemistry.
Poly(methacryloxypropylmethylsiloxane)
A UV-curable silicone: the pendant methacrylate polymerises by free radicals while the siloxane backbone supplies the release and flexibility. The basis of radiation-cured release liners.
Poly(methyl(2-(4-hydroxyphenyl)ethyl)siloxane)
A phenol-functional silicone, used to build silicone segments into epoxy and phenolic networks through the hydroxyl rather than through a silicon-bound group.
Poly(methyl(2-(4-methoxyphenyl)ethyl)siloxane)
An electron-rich aralkyl silicone with a higher refractive index than the plain phenethyl fluid, used in optical couplants and index-matching gels.
Poly(methyl(2-carboxyethyl)siloxane)
A shorter-tether carboxy silicone. With only two carbons between silicon and the acid, the carboxyl is close enough to catalyse cleavage of its own siloxane backbone under heat.
Poly(methyl(2-hydroxyethyl)siloxane)
The shortest carbinol tether that is still stable. With only two carbons the hydroxyl can reach back to the silicon, so these fluids are markedly less robust than the hydroxypropyl grades.
Poly(methyl(2-phenylpropyl)siloxane)
A branched aralkyl silicone fluid sold as a high-refractive-index, non-volatile alternative to poly(methylphenylsiloxane) for optical couplants.
Poly(methyl(3-(2-hydroxyethoxy)propyl)siloxane)
A silicone polyether in miniature: one oxyethylene unit and a terminal hydroxyl on each silicon, enough to make the fluid water-dispersible and to give it the wetting behaviour that pure silicones lack.
Poly(methyl(3-(dimethylamino)propyl)siloxane)
A tertiary-amine silicone. Unlike the primary aminopropyl fluid it cannot condense with itself on ageing, and it is quaternised after polymerisation to give cationic silicone surfactants.
Poly(methyl(3-(triethoxysilyl)propyl)siloxane)
A silicone that carries its own moisture-cure crosslinker: the pendant triethoxysilane hydrolyses and condenses on exposure to air, turning the fluid into a network without any second component.
Poly(methyl(3-acetoxypropyl)siloxane)
A protected carbinol silicone. The acetate is carried through the polymerisation and then hydrolysed to the hydroxypropyl fluid, avoiding the side reactions a free hydroxyl causes during ring opening.
Poly(methyl(3-bromopropyl)siloxane)
A more reactive precursor than the chloropropyl fluid: the primary bromide is displaced under milder conditions, which matters when the nucleophile is a base that would attack the siloxane backbone at higher temperature.
Poly(methyl(3-isocyanatopropyl)siloxane)
An isocyanate-functional silicone that reacts directly with polyols and amines. It has to be kept dry: water converts the pendant NCO to an amine and then to a urea crosslink.
Poly(methyl(3-methoxypropyl)siloxane)
An ether-functional silicone. One oxygen in the tether is enough to make the fluid wet polar substrates that PDMS beads up on.
Poly(methyl(3-sulfopropyl)siloxane)
An anionic silicone. The strong acid is fully dissociated at any pH, which makes the fluid a silicone polyelectrolyte rather than the weak-acid behaviour the carboxypropyl version shows.
Poly(methyl(4-methylphenyl)siloxane)
A methylated aryl siloxane; the extra methyl lowers the melting point of the fluid relative to poly(methylphenylsiloxane) while keeping most of the refractive index gain.
Poly(methyl(4-vinylphenyl)siloxane)
A styrenic silicone: the pendant vinylbenzene copolymerises with styrene and acrylics by free radicals, which is how silicone segments are built into otherwise all-organic chains.
Poly(methyl(tridecafluorooctyl)siloxane)
A long perfluoroalkyl silicone. The tails crystallise into a bilayer that presents only CF3 groups at the surface, giving the lowest surface energies of any silicone - and losing them above the side-chain melting point.
Poly(methylallylsiloxane)
The allyl group is one carbon further from silicon than a vinyl, which makes it react more slowly in hydrosilylation but leaves the resulting Si-C link less strained.
Poly(methylbenzylsiloxane)
The benzyl group raises the refractive index while the methylene spacer keeps the ring from conjugating with silicon, so the fluid stays colourless on heat ageing better than the phenyl siloxanes.
Poly(methylbutylsiloxane)
Alkyl-modified silicone fluid. Each added carbon raises the solubility parameter towards that of a hydrocarbon and lowers the surface activity that pure PDMS is used for.
Poly(methylcyclohexylsiloxane)
A cycloaliphatic silicone. The ring stiffens the chain like a phenyl group without the UV absorbance, which matters in optical silicones exposed to short wavelengths.
Poly(methylcyclopentylsiloxane)
A cycloaliphatic silicone with a five-membered ring, which stiffens the chain less than the cyclohexyl analogue because the ring itself is more flexible.
Poly(methyldecylsiloxane)
The C10 alkylmethyl fluid, widely used as an emollient where a silicone feel is wanted with hydrocarbon solubility.
Poly(methyldodecylsiloxane)
A comb silicone. The C12 side chains associate with each other and with hydrocarbon waxes, which is the property used in personal-care emollients and in wax-crystal modification.
Poly(methylethoxysiloxane)
An alkoxy-functional siloxane that keeps condensing on exposure to moisture. Used as a masonry water repellent and as a silica precursor, where the ethoxy groups hydrolyse in place.
Poly(methylethylsiloxane)
One methylene beyond PDMS. The asymmetric substitution frustrates the crystallisation that gives PDMS its -40 C melting transition, so this stays amorphous to lower temperatures.
Poly(methylheptylsiloxane)
A C7 alkyl silicone. By this length the fluid is fully miscible with mineral oil and has lost most of the surface activity that shorter silicones show.
Poly(methylhexadecylsiloxane)
A C16 comb silicone whose side chains melt near room temperature, so the material changes from waxy to fluid over a narrow range - the property used in phase-change and thermally switchable coatings.
Poly(methylhexylsiloxane)
The hexyl substituent makes this miscible with mineral oil, which is why alkylmethyl siloxanes of this length are used as antifoams in systems where PDMS itself would be rejected.
Poly(methylhydrosiloxane)
A silicone with a reactive hydrogen on every silicon, which makes it the crosslinker rather than the product. Those Si-H bonds add across vinyl groups under a platinum catalyst, which is the hydrosilylation cure behind every addition-cure silicone rubber, and they also serve as a cheap, air-stable reducing agent in organic synthesis.
Poly(methylisobutylsiloxane)
Branching the alkyl group keeps the chains from packing, so this stays a fluid where the linear butyl analogue begins to order.
Poly(methylnonylsiloxane)
A C9 comb silicone, at the length where the side chains begin to interact with each other rather than simply with the solvent.
Poly(methyloctadecylsiloxane)
The C18 alkyl silicone. The side chains crystallise well above room temperature, so this is a waxy solid rather than a fluid despite a backbone that is among the most flexible known.
Poly(methyloctylsiloxane)
The other direction from the dimethyl fluid: a long alkyl chain making the silicone more hydrocarbon-like, so it mixes with oils that plain PDMS will not and holds non-polar analytes more strongly as a chromatographic phase. Between this and the cyanopropyl version the siloxane backbone spans nearly the whole polarity range from one architecture.
Poly(methylpentylsiloxane)
The C5 alkylmethyl siloxane, between the butyl and hexyl fluids in the smooth progression from silicone-like to hydrocarbon-like behaviour.
Poly(methylphenylsiloxane)
A silicone with a phenyl in place of one methyl, which is how silicone fluids are stopped from crystallising and pushed to higher temperatures. The bulky aromatic disrupts packing, so the oil stays liquid far below where PDMS would freeze, and it raises the refractive index enough to matter for optical encapsulants. It also absorbs radiation damage better than the all-methyl version, which is why phenyl silicones appear in nuclear and space applications.
Poly(methylpropylsiloxane)
A siloxane fluid whose propyl group raises compatibility with hydrocarbon oils while keeping the low-temperature flexibility of the Si-O backbone.
Poly(methyltetradecylsiloxane)
A comb silicone between the dodecyl and octadecyl grades, at the point where the side chains first crystallise near room temperature.
Poly(methylundecenylsiloxane)
A long tether ending in a terminal alkene. The distance between silicon and the reactive end lets a graft be attached without the siloxane backbone crowding it - the usual way silicones are grafted onto surfaces and particles.
Poly(methylvinylsiloxane)
The other half of an addition-cure silicone: the vinyl groups here are what the Si-H of a hydride siloxane adds across. In practice a few mole percent of vinyl is copolymerised into an otherwise dimethyl chain, and that fraction sets the crosslink density and therefore the modulus of the cured rubber.
N
Poly(nonafluorohexylmethylsiloxane)
A longer-tail fluorosilicone than the trifluoropropyl standard. More fluorine means better fuel and solvent resistance, but the tails crystallise and the fluid stiffens.
O
Poly(octylhydrosiloxane)
A long-chain hydride fluid. The octyl group keeps it soluble in oils and waxes, so it can hydrosilylate substrates that a methylhydrosiloxane would not wet.
P
Poly(phenethylmethylsiloxane)
The two-carbon spacer keeps the phenyl ring off silicon, so this raises the refractive index like poly(methylphenylsiloxane) without the same loss of chain flexibility.
Poly(phenylhydrosiloxane)
A hydride-functional aryl siloxane used as the crosslinker in high-refractive-index addition-cure silicones, where a methylhydrosiloxane would drag the index back down.
Poly(phenylsilsesquioxane)
A silicone in which each silicon carries one organic group and one and a half oxygens, so the structure is a cage or a ladder rather than a chain - halfway between a silicone and silica. The idealised repeat is drawn here; real material is a mixture of cages, ladders and incompletely condensed fragments, which is why its properties depend so strongly on cure history.
Poly(phenylvinylsiloxane)
Carries both the refractive-index-raising phenyl and the vinyl group that hydrosilylation cure needs, so it appears as the resin component of high-index LED encapsulants.
Poly(propylphenylsiloxane)
A higher-alkyl aryl siloxane; the longer chain suppresses crystallisation, which is why these fluids stay pourable at temperatures where poly(methylphenylsiloxane) has set.
S
Silanol-terminated poly(dimethylsiloxane), 1000 cSt
The base polymer of a condensation-cure RTV silicone: a Si-OH at each end, which crosslinks with an alkoxysilane and a tin or titanium catalyst, releasing alcohol. Two published numbers here disagree and it is worth knowing which to use - the titrated 0.055-0.060 eq/kg implies about 17,400 g per silanol, while the nominal 26,000 molecular weight would imply 13,000. The titration is what the cure is stoichiometric against, so that is the equivalent weight quoted, and no molar mass is asserted. Terminal silanols condense under mild acid and base alike, which is why these grades have a shelf life that dry storage does not fully solve.
Polysilazane
A backbone of alternating silicon and nitrogen, and a preceramic polymer: it is applied as a liquid and then converted by heat or by moisture to silica or silicon nitride, taking the shape it was coated in. That lets a ceramic coating be painted onto a substrate that could never survive ceramic processing, which is how glass-like anti-graffiti and anti-corrosion layers are applied at room temperature.
T
Poly(trifluoropropylmethylsiloxane)
Silicone that survives contact with fuel. Ordinary PDMS swells badly in hydrocarbons, which rules it out for seals in engines and aircraft; replacing one methyl per silicon with a trifluoropropyl group raises the solubility parameter enough to resist that swelling while keeping the siloxane backbone's flexibility down to about -60 C.