Polysilicone-8 or Silsesquioxane, is a silicone chemical compound: 3-Thiopropyl methyl siloxane, polymer with dimethylsiloxane, S-ester with polymer of 2-propenoic acid and methyl 2-methyl-2-propenoate.

The name describes the structure of the molecule:

The name defines the structure of the molecule:

• The "poly" in Polysilicone-8 indicates that it is a polymer, a large molecule composed of repeated subunits.
• The "silicone" part of the name refers to the fact that it is a silicone-based polymer, which means that it contains silicon atoms.
• The number "8" in Polysilicone-8 refers to the length of the polymer chain or the degree of polymerization, with higher numbers indicating longer or more complex chains.

The synthesis process takes place in different steps:

• Preparation. The main monomers for the synthesis of Polysilicone-8 are silanes or siloxanes, which contain silicon atoms.
• Polymerization. Monomers react together in a polymerization reaction with the formation of multiple bonds to create a large, complex molecule. The reaction is carried out at high temperatures and can be catalyzed by a variety of substances, including acids, bases or metal catalysts.
• Purification. The reaction mixture is purified to isolate Polysilicone-8 and involves processes such as distillation, filtration and drying.
• Quality control test. The final product is tested to ensure it meets the required specifications. This may involve testing for molecular weight, purity, viscosity, and other physical and chemical properties.

What it is used for and where

Polysilicone-8 is a silicone polymer that is often used in cosmetics and personal care products due to its ability to provide a silky feel and improve product spreadability. 

Silicones have high chemical stability but low biodegradability and high bioaccumulation potential.

Cosmetics

Antifoaming agent. The constituent factors for foam stabilisation are the concentration of nanoparticles and hydrophobicity. Foam, even when used in separation operations such as fractionation or flotation, can cause a decrease in density and a deterioration in quality in cosmetic products. The defoaming agent (non-polar oil, silicone oils, hydrophobic solid particles or mixtures of both) is strongly influenced by viscosity and, to an almost directly proportional extent, concentration. However, defoamers can carry an irreversible source of contamination.

Hair conditioning agent. A large number of ingredients with specific purposes can co-exist in a hair shampoo: cleansers, conditioners, thickeners, mattifying agents, sequestering agents, fragrances, preservatives, special additives. However, the indispensable ingredients are the cleansers and conditioners as they are necessary and sufficient for hair cleansing and manageability. The others act as commercial and non-essential auxiliaries such as: appearance, fragrance, colouring, etc. Hair conditioning agents have the task of increasing shine, manageability and volume, and reducing static electricity, especially after treatments such as colouring, ironing, waving, drying and brushing. They are, in practice, dispersing agents that may contain cationic surfactants, thickeners, emollients, polymers. The typology of hair conditioners includes: intensive conditioners, instant conditioners, thickening conditioners, drying conditioners.

Safety

It is an ingredient that has a high bioaccumulation and persistence, however in cosmetic use this ingredient is considered safe.