Is Ethylene Glycol the Same as Polyethylene Glycol?
No. Ethylene glycol and polyethylene glycol are different compounds despite their similar names. Ethylene glycol is a small molecule with the formula C2H6O2, while polyethylene glycol is a polymer made of repeating ethylene oxide units. They differ in molecular structure, physical state, toxicity and applications, and they are identified by different CAS numbers.
What Is Ethylene Glycol?
Ethylene glycol, also known as monoethylene glycol or 1,2-ethanediol, is a simple diol with the CAS registry number 107-21-1. It is a colorless, odorless, viscous liquid at room temperature, with a boiling point of 197.3 degrees Celsius and a freezing point of minus 12.9 degrees Celsius. It is completely miscible with water. Ethylene glycol is used mainly as antifreeze and coolant, as a raw material for polyester fibers and PET resins, and in industrial heat transfer systems. It is toxic if ingested.
What Is Polyethylene Glycol?
Polyethylene glycol, abbreviated PEG, is a polyether polymer built from repeating ethylene oxide units, with the CAS registry number 25322-68-3. Its appearance depends on molecular weight. Below a molecular weight of about 700, PEG is a liquid. Between about 700 and 900, it is a semisolid. Above about 900, it is a waxy solid that can be supplied as flakes or powder. PEG has low toxicity and is widely used in pharmaceuticals, cosmetics, personal care products, lubricants and industrial coatings.
Key Differences in Applications
Because of its toxicity, ethylene glycol is restricted to industrial applications such as antifreeze, coolants and polyester production, where it is not part of consumer products intended for ingestion. Polyethylene glycol, by contrast, is accepted as an excipient in medicines, foods and cosmetics, and different molecular weight grades are selected for different functions, from liquid carriers to solid binders. The two products therefore cannot be substituted for each other.
How to Choose the Right Product
Choose the product according to the application and the required specification. For heat transfer, antifreeze and polyester feedstock, ethylene glycol is the standard choice. For pharmaceutical, cosmetic, personal care and food contact applications, select the appropriate polyethylene glycol grade and verify its molecular weight, purity and regulatory compliance. Always confirm the CAS number and certificate of analysis with the supplier before purchasing.
Frequently Asked Questions
Is ethylene glycol the same as polyethylene glycol? No, ethylene glycol is a single small molecule while polyethylene glycol is a polymer, and they have different CAS numbers and uses.
What is the CAS number of ethylene glycol? The CAS registry number of ethylene glycol is 107-21-1.
What is the CAS number of polyethylene glycol? The CAS registry number of polyethylene glycol is 25322-68-3.
Why does PEG appear as liquid or solid? The physical state depends on molecular weight; low-molecular-weight PEG is liquid, while high-molecular-weight grades are waxy solids, flakes or powders.
Can polyethylene glycol be used in pharmaceuticals? Yes, PEG is widely used as an excipient in pharmaceuticals and cosmetics because of its low toxicity and versatile solubility.