Dimethicone

Polydimethylsiloxane, sometimes called dimethicone, is a silicone. The chemical formula is C2H6OSi. Dimethicone is a silicone based polymer contraining two methyl groups. As it is a liquid mixture, it is clear, unreactive, non-toxic, and non-flammable. It can be used as a skin conditioning agent and can be found in Johnson's Baby Lotion.

The [|chemical formula] for PDMS is CH3[Si(CH3)2O]//n//Si(CH3)3, where //n// is the number of repeating [|monomer] [SiO(CH3)2] units. Industrial synthesis can begin from dimethyl [|chlorosilane] and [|water] by the following net reaction: //n// Si(CH3)2Cl2 + //n// H2O → [Si(CH3)2O]//n// + 2//n// HCl During polymerization, this reaction evolves potentially hazardous [|hydrogen chloride] gas. For medical uses, a process was developed in which 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. Under ideal conditions, each molecule of such a compound becomes a branch point. This 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. 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). PDMS [|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 PDMS' unusually high level of [|viscoelasticity].

Many people are indirectly familiar with PDMS because it is an important component in [|Silly Putty], to which PDMS imparts its characteristic viscoelastic properties. [|[6]] The rubbery, vinegary-smelling silicone caulks, adhesives, and aquarium sealants are also well-known. PDMS 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. PDMS has also been used as a filler fluid in [|breast implants], although this practice has decreased somewhat, due to safety concerns.