When it comes to polyethylene glycol, I believe many friends will feel strange. However, if I tell you that it is not difficult to find polyethylene glycol around us, for example, it is indispensable in cosmetics, toothpaste and medicines, I am afraid that many friends will inevitably ask, why does polyethylene glycol appear in these products? What does it do? Is it toxic to humans? So today, I will give you a brief introduction to this compound with wide applications.
Properties
Polyethylene glycol (PEG) has the word “poly” in its name, which indicates that it is a polymer compound. From Figure 1 we can see that polyethylene glycol can be seen as being derived from repeated repetitions of several CH2CH2O. But what is its connection with ethylene glycol? As we all know, “alcohol” refers to an organic compound with a hydroxyl group (-OH). The alcohol compound we are most familiar with is probably ethanol, which contains two carbon atoms, one of which is connected to the hydroxyl group. If we attach another carbon atom to a hydroxyl group, ethanol becomes ethylene glycol. Although ethylene glycol is not as famous as its “close relative” ethanol, it is indispensable in our daily lives. For example, the coolant used in cars is made by mixing water and ethylene glycol in a certain proportion.
Figure 1 Chemical structures of polyethylene glycol (left) and ethylene glycol (right)
Now let us imagine what would happen if two ethylene glycol molecules reacted with each other and lost one molecule of water? From Figure 2 we can see that the original two molecules are connected together to become one molecule. The ethylene glycol molecule has two carbon atoms, but the newly formed molecule has four carbon atoms. The molecule has obviously become longer. If a third ethylene glycol molecule comes over, it can react with the new molecule and lose a molecule of water. As a result, the new molecule becomes longer. But that’s not all. This molecule can also react with the fourth, fifth or even more ethylene glycol molecules to increase in length, eventually forming polymer compounds with molecular weights ranging from a few hundred to tens of thousands. This is the origin of the name of the polymer compound polyethylene glycol. However, in fact, the synthesis of polyethylene glycol is mainly achieved through another small molecule, ethylene oxide, so polyethylene glycol is often called polyethylene oxide (polyethylene oxide, simply thixotropic agent). Called PEO). Polyethylene glycol with a relatively low molecular weight (for example, several hundred) is usually a viscous liquid, but with a slightly higher molecular weight it becomes a white solid.
Effects and functions
The common polymer compounds in our daily life are usually insoluble in water, but polyethylene glycol has high solubility in water. This is because the oxygen atoms in its molecules interact strongly with water molecules. The interaction is called a hydrogen bond. When we put polyethylene glycol into water, each polyethylene glycol molecule will be closely mixed with many water molecules, so even polyethylene glycol molecules with a molecular weight of tens of thousands will not form in water. Dissolves quickly. Polyethylene glycol is not only highly soluble in water, but also has very good solubility with many organic compounds in ethanol. Due to this unique property, polyethylene glycol is widely used in various daily chemicals, such as cosmetics, toiletries and toothpaste.
One of its main functions is to act as a solvent or surfactant, helping components with different chemical properties to mix together evenly. Also, polyethylene glycol has a strong interaction with water, so the polyethylene glycol added to these products helps keep it moist. In addition, some daily chemical products require a certain viscosity, and polyethylene glycol comes in handy again at this time. Since low molecular weight polyethylene glycols are viscous liquids, they can significantly increase the viscosity of these cosmetics.
