Polyurethane-21 is an inorganic chemical compound, a segmented block copolymer derived from urethane and synthesised from isocyanates.

The name describes the structure of the molecule:

• "Polyurethane" is a term that describes a class of polymers widely used in various applications due to their versatility and desirable properties such as durability, flexibility and abrasion resistance and temperature variations.
• "21" is a reference to the specific type or grade of polyurethane, which can be characterized by such factors as the types of isocyanates and polyols used, their relative amounts, and the presence of any additives. . This is a designation used to differentiate different molecular structures or variants of the polymer. In cosmetic chemistry, these numbers can help formulators identify specific characteristics or behaviors of a given ingredient, particularly when a chemical family has multiple derivatives or forms.

Significant substances used in the production method:

methylenedicyclohexanediisocyanate, polymer with 2,2-di(hydroxymethyl)propanoic acid, 2,2'-oxybisethanol/2-oxepanone copymer, tris(2-hydroxyethyl)amine.

Description of raw materials used in production and their functions.

• Isophorone Diisocyanate. Provides isocyanate groups for polyurethane formation.
• Dimethylol Propionic Acid. A molecule offering hydroxyl groups to react with the isocyanate groups.
• Polyester of hexanedioic acid, isophthalic acid, and 1,6-hexanediol. Acts as a polyol component in the system, providing additional hydroxyl groups for polyurethane formation.
• Ethylene Diamine. Acts as a chain extender and provides amine functionality to react with any remaining isocyanate groups.
• Triethylamine. Used to neutralize the dimethylol propionic acid in the polymer intermediate.

Step-by-step summary of industrial chemical synthesis process.

• Isophorone diisocyanate reacts with dimethylol propionic acid to form a polyurethane intermediate.
• This intermediate then reacts with the polyester formed from hexanedioic acid, isophthalic acid, and 1,6-hexanediol.
• Ethylene diamine is then added as a chain extender to react with any free isocyanate groups in the polymer.
• The resultant acid intermediate is then neutralized with triethylamine, stabilizing the polymer structure and forming the final polyurethane.

What it is used for and where

Polyurethane-21 is a restricted ingredient as III/62  a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported: Trialkylamines, trialkanolamines and their salts

Cosmetics

Film-forming agent. It produces a continuous ultra-thin film with an optimal balance of cohesion, adhesion and stickiness on the skin or hair to counteract or limit damage from external phenomena such as chemicals, UV rays and pollution.

It appears as a white powder or colorless liquid.

Safety

Urethane (also called ethyl carbamate) is a by-product of fermentation and is considered a genotoxic agent.

Polyurethanes are rather complex, inert and biostable materials that are also used in biomedical applications. They are typically synthesised by the reaction of a glycol or polyol with polyisocyanate or diisocyanate. It is known that exposure to isocyanates can cause asthma, contact allergies, conjunctival and skin irritation. However, a study by the Cosmetic Ingredient Review Expert Panel in 2017 found that the rates of harmful residues are not significant for human health.