Peg/Ppg-18/18 Dimethicone is an inorganic chemical compound, a Dimethicone by-product.

The name defines the structure of the molecule:

• "Peg/Ppg-18/18" refers to a polyethylene glycol (PEG) and polypropylene glycol (PPG) copolymer that has an average molecular weight of 18,000 for both PEG and PPG components.
• "Dimethicone" is a type of silicone oil with two methyl groups attached to the silicone atom.

The synthesis process takes place in several stages:

• Polymerisation: ethylene oxide and propylene oxide are polymerised separately to form polyethylene glycol (PEG) and polypropylene glycol (PPG) respectively by a ring-opening polymerisation process, where monomers of oxide react in the presence of a catalyst.
• Copolymerization: PEG and PPG are copolymed to form a PEG/PPG copolymer with the reaction of PEG and PPG chains in the presence of a catalyst that can initiate the formation of covalent bonds between them.
• Reaction with dimethicone: PEG/PPG copolymer reacts with dimethicone to form Peg/Ppg-18/18 dimethicone with the use of a coupling agent that can react with the hydroxyl groups on the PEG/PPG copolymer and the silanol groups on the dimethicone to form a covalent bond between them.
• Purification: The resulting dimethicone Peg/Ppg-18/18 is purified to remove any materials and impurities not reacted through distillation or filtration.
• Packaging: The purified Dimethicone Peg/Ppg-18/18 is packaged and stored for use in various applications, such as in cosmetics  and personal care products where it is used for its emulsifying and conditioning properties of the skin.

What it is used for and where

Cosmetics

Surfactant - Emulsifying agent. Emulsions are thermodynamically unstable and are used to soothe or soften the skin and emulsify, so they need a specific, stabilising ingredient. This ingredient forms a film, lowers the surface tension and makes two immiscible liquids miscible. A very important factor affecting the stability of the emulsion is the amount of the emulsifying agent. Emulsifiers have the property of reducing the oil/water or water/oil interfacial tension, improving the stability of the emulsion and also directly influencing the stability, sensory properties and surface tension of sunscreens by modulating the filmometric performance.

Safety

Dimethicone ((polydimethylsiloxane) is a chemical compound, a high molecular weight polymer derived from silicone, a chemically inert mixture of linear methylated siloxane polymers. The term 'dimeth' denotes two methyl groups bonded to the silicone molecule that provide the formation of dimethicone. It possesses a pronounced viscoelasticity characteristic and is hydrophobic, thus adding shine and slipperiness when applied to hair or skin. It forms a kind of barrier that prevents exogenous substances from entering the stratum corneum and at the same time prevents water loss. It is also UV-resistant, non-greasy and cost-effective. At low concentrations it is considered by the US FDA (Food and Drug Administration) to be a skin protector with a good degree of safety.

It is therefore considered safe when formulated to be non-irritating in cosmetic products as, given its high molecular weight, it is poorly absorbed by the skin or scalp.

PPG (Polypropylene glycol) in small quantities is a safe, biocompatible, biodegradable polymer that produces pyruvic acid, a metabolite that our body uses to produce metabolic energy.

And now let us talk about PEGs.

Since the PEG (Polyethylene glycol) family is very numerous and can be found in cosmetic, industrial, pharmaceutical, medical and other products, we need to make an introductory statement on the subject, which is rather complex from a safety point of view because these products not only come into contact with the skin, but, as in the case of medical products, are ingested.

PEGs (polyethylene glycol) polymerise condensed ethylene oxide and water and are referred to as polyethylene glycols, but are actually complex chemical components, polymers bonded together. For example, plastic is polyethylene and has a hard consistency, while polyethylene combined with glycol forms a liquid. PEGylation is produced not only as etherification, but also as transesterification, which is the transformation of an alcohol by an ester.

The number appearing after the abbreviation PEG represents the molecular weight and the higher this number is, the less it penetrates the skin.