Properties of Polyethylene Glycol
- Miralax--A common laxative that uses poly(ethylene glycol)
A common surfactant, poly(ethylene glycol) can be found in many household products. As it is nontoxic, the FDA allows the use of poly(ethylene glycol)--or PEG--in toothpaste and laxatives. One common use in the pharmaceutical industry is a laxative, Miralax. This synthetic polymer, which is available in many different molecular weights (and forms), is also used in cosmetics.
The high viscosity (found only in low molecular weight PEGs) allows poly(ethylene glycol) to be used in so many different products.
- Polymer structure of poly(ethylene glycol)
Poly(ethylene glycol) is a condensation polymer, or step-growth polymer. It is formed by the reaction of two monomers (ethylene oxide). They will condense to form a dimer (two of the same monomer joined together).
Condensation polymers are more stable than addition polymers. They are less susceptible to branching on the monomer units. Branching tends to make a polymer weak and of low density. This is why poly(ethylene glycol), a strong condensation polymer, has so many uses. Due to PEG being a condensation polymer, it has a high density of 1.1-1.2g/cm^3. This is higher than the density of water (1.0g/cm^3).
- Poly(ethylene glycol) is amphiphilic, meaning it is soluble in both aqueous and organic solvents. This is uncommon in chemistry and increases available uses for PEG since it can be used in almost any environment. Synthetic polymers are also useful because they have no boiling point. They will degrade before boiling, so poly(ethylene glycol) can survive in the human body.
- Due to its relatively low number of repeating monomer units (n≈9), poly(ethylene glycol) tends to have a relatively low molecular weight compared to many other polymers (about n≈100 for polystyrene).
However, a higher number of repeating units can also be found within the PEG universe. The molecular weight can be anywhere from 190g to 7000g. The lower weight polymers are generally in a clear liquid form and could be what is found in personal lubricants and laxatives. Higher molecular weight poly(ethylene glycol) is a more waxy, white polymer. Each different weight has a slightly different form, giving the polymer vastly numerous uses in the pharmaceutical industry.
- Although Poly(ethylene glycol) is stable when used correctly and under "ordinary conditions," as it is heated toward decomposition temperature, carbon monoxide gas and carbon dioxide gas may form.
PEG has a flammability rating of 1. This means that it is combustible if it is heated. This is the lowest rating other than 0. Sucrose (table sugar) has a flammability rating of 2.