What Is Dipropylene Glycol?
Dipropylene Glycol is a colorless liquid with viscosity at room temperature.
Dipropylene Glycol has a melting point of -40°C and a boiling point of 231.8°C. It has a molecular structure similar to the dehydration-condensation of two propylene glycols.
Dipropylene Glycol used to be a by-product of the propylene glycol (PG) production process using the propylene oxide (PO) hydration reaction. In recent years, as the demand for dipropylene glycol has increased, methods to produce it without relying on side reactions in the production of PG are being commercialized.
Uses of Dipropylene Glycol
Dipropylene Glycol is used as a raw material for unsaturated polyester resins, which are used to make fiber-reinforced plastics (FRP), as a glycol component in benzoate plasticizers, and as a raw material for cosmetics.
Dipropylene Glycol is used for moisturizer or preservative purposes to increase stratum corneum moisture content, especially in the field of cosmetics.
The following is a list of cosmetic products in which dipropylene glycol is used:
- Skin care cosmetics
- Makeup cosmetics
- Makeup bases
- Sheet and mask products
- Sunscreens
- Facial cleansing soaps
- Shampoos and conditioners
- Hair coloring products
- Hair styling products
- Nail polish
- Perfumes
Properties of Dipropylene Glycol
Dipropylene Glycol is characterized by its high hydrophilicity despite being an organic compound. It has both hydroxyl (-OH) and ether (-O-) groups in the molecule, giving it the properties of a hydrophilic compound.
Dipropylene Glycol is completely miscible and soluble with water. It is also easily soluble in polar organic solvents such as alcohols.
Molecular Structure of Dipropylene Glycol
The molecular structure of dipropylene glycol is literally two propylene glycols connected together. Specifically, it has a molecular structure in which the -OH groups of the two propylene glycols are dehydrated and condensed together. There is a -OH at each end of the molecular chain, with a single ether bond between the two ends flanked by hydrocarbons.
The molecular formula is simply HO (C3H6O) 2H, but the part in parentheses is generally branched rather than linear. Propylene glycol contains isomers with different molecular structures depending on which two of the three carbons (C-C-C) have -OH groups attached.
Assuming a dehydration-condensation reaction between such propylene glycols, various isomers of dipropylene glycol are produced depending on the reaction pattern of the -OH group. Therefore, dipropylene glycol used as an industrial raw material is usually a mixture of various isomers.
Other Information on Dipropylene Glycol
How Dipropylene Glycol is Produced
Dipropylene Glycol, like Propylene Glycol or Tripropylene Glycol, is generally made from Propylene Oxide. Specifically, it is obtained by ring opening of propylene oxide in the presence of water.
In this production process, propylene glycol is obtained as the main product, while dipropylene glycol is obtained as a byproduct. Therefore, dipropylene glycol is not necessarily produced in large quantities.
Methods to specifically produce only dipropylene glycol have been studied, but they have not yet become the mainstream production method.