What is Monopropylene Glycol?

by Kate Onissiphorou

Monopropylene glycol also known simply as propylene is a viscous, colourless liquid with a distinct sweet taste (but please don’t drink it). Almost odourless, it’s both miscible with water and hygroscopic, i.e. it attracts and absorbs moisture. 

The chemical formula of monopropylene glycol is C3H8O2, which can also be written as:


This formula tells us that it has two alcohol groups, which make it a diol. Its systematic IUPAC name is therefore propane-1,2-diol. Monopropylene glycol has the following physical properties:

  • Molecular mass: 76.095 g·mol−1
  • Exact mass: 76.052429 g/mol
  • Flashpoint: 98.9 °C  
  • Boiling point: 188.2 °C  
  • Melting point/freezing point threshold: −59 °C  
  • Vapour pressure: 0.13 mm Hg at 25 °C
  • Density: 1.0361 g/cu cm at 20 °C. 

What is Monopropylene Glycol Used For?

From antifreeze to food additives, monopropylene glycol has a wide range of industrial and commercial applications. Some of the most common uses are outlined below.

  1. Polymers
    Approximately 45% of the industrial use of propylene glycol is in the manufacture of various polyester products. It’s used as a chemical feedstock in the large-scale production of unsaturated polyester resins, which are turned into thermoset plastic. During this process, unsaturated maleic anhydride is mixed with isophthalic acid to form a copolymer. The partially unsaturated copolymer then undergoes further crosslinking. Meanwhile, the propylene glycol reacts with propylene oxide to produce oligomers and polymers, which are then used to make polyurethanes.
  2. Food additives
    Monopropylene glycol is considered safe for consumption due to its low toxicity, especially in small concentrations. As a result, it’s often used as an additive in various food and beverage products, including coffee-based drinks, ice cream, soda, and whipped cream.
  3. Pharmaceutical products
    Several types of pharmaceutical and personal care products contain monopropylene glycol. It’s a common ingredient in alcohol-based sanitisers, for instance, because it helps to prevent the skin from drying.

    Grinding coffee beans in a tank in a factory
    Monopropylene glycol is used as an additive in coffee-based drinks

    Monopropylene glycol is also used as a solvent in some oral, injectable and topical medications. Capable of dissolving drugs that are insoluble in water, it acts as a good solvent and carrier for medicines such as benzodiazepine tablets.

  4. Antifreeze
    A person pouring blue antifreeze into a car engine for the window screen.The low freezing point and high boiling point of monopropylene glycol make it a good antifreeze and coolant, respectively. When mixed with water at 50% solution, monopropylene glycol significantly lowers the freezing point of water and prevents ice crystals from forming during cold weather. As a result, it’s commonly used to de-ice aircrafts before take-off.
  5. E-cigarettes
    Monopropylene glycol is one of the main ingredients in the liquid found in electronic cigarettes. Close up of a woman inhaling from an e-cigaretteThe heat caused by inhalation vaporises the chemicals contained in the liquid, creating the characteristic e-cigarette ‘smoke’.

Is Monopropylene Glycol Safe?

Monopropylene glycol is listed under CAS No: 57-55-6. It’s not classified as posing a significant danger to health and is considered safe enough to be used as an additive in food and medicines. It’s also safe to transport and does not ignite easily.  

However, like many other substances, the risk of toxicity rises as the concentration increases. Generally, monopropylene glycol becomes toxic at levels above 18 mg/dL, although this can vary depending on an individual’s body weight, age and health status. 

Propylene Glycol vs Monopropylene Glycol

Propylene glycol is synonymous and interchangeable with monopropylene glycol. So is there a difference? In a nutshell, no. They are simply alternative names for the same chemical compound that contains alcohol groups and propyl groups. 

The systematic IUPAC name of this chemical is propane-1,2-diol. Monopropylene glycol/ propylene glycol can also be called:

  • α-Propylene glycol
  • 1,2-Propanediol
  • 1,2-Dihydroxypropane
  • Methyl ethyl glycol
  • Methylethylene glycol

The Use of Monopropylene Glycol in Medicine

Monopropylene glycol is mainly used in medicine and other pharmaceutical products as a solvent and carrier. Its miscibility with water means it can dissolve medicines that are otherwise insoluble in water. 

Another benefit of monopropylene glycol is that it can prevent topical medicines, such as creams and ointments, from drying out. Thanks to its hygroscopic properties, it can also help to keep the skin moisturised.

Monopropylene Glycol MSDS

The material safety data sheet (MSDS) for monopropylene glycol contains useful information about the toxicity and hazards of this popular solvent, along with a description of the first aid measures in case of an emergency.

It may also include other important details, such as the concentration. All of the material safety data sheets for the chemicals we supply are available to download from our website

If you’re a business looking to buy high-quality monopropylene glycol, visit our online shop today. Available in a variety of batch sizes, from 2.5 litres right up to 200 litre drums, you’re sure to find the right solution for your needs. And if you need any help, simply get in touch with our friendly customer service team.


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