Polyethylene glycol (PEG) is a polyether compound that is widely used in various industries and applications. It is a synthetic polymer composed of repeating units of ethylene glycol, which is a simple organic compound with the chemical formula HO-CH2-CH2-OH. The repeating units in PEG are linked together by ether (-O-) bonds.

Here are some key characteristics and uses of polyethylene glycol:

1. Chemical Structure: PEG is a linear or branched polymer with a general formula of HO-(CH2-CH2-O)n-H, where "n" represents the number of ethylene glycol repeating units. The molecular weight and properties of PEG can vary depending on the length of the polymer chain.

2. Water Solubility: PEG is highly water-soluble, which makes it useful in various applications, including pharmaceuticals, cosmetics, and food products.

3. Hygroscopic: PEG has hygroscopic properties, meaning it can absorb and retain water. This property is often used in the formulation of skincare products and pharmaceuticals to help moisturize the skin or deliver drugs.

4. Medical and Pharmaceutical Uses: PEG is commonly used in the pharmaceutical industry as an excipient (inactive ingredient) in various drug formulations. It can be found in oral liquids, ointments, and suppositories. PEG is also used in the production of laxatives, such as PEG 3350 (commonly known as Miralax or GlycoLax), which is used to treat constipation.

5. Cosmetic and Personal Care Products: PEG is used in cosmetics and personal care products as a thickening agent, stabilizer, and emulsifier. It can be found in products like creams, lotions, shampoos, and soaps.

6. Industrial Applications: PEG has various industrial applications, including as a lubricant and mold release agent. It is also used in the production of plastics, as a component in antifreeze formulations, and in the synthesis of certain chemicals.

7. Medical Imaging: PEG-based contrast agents are used in medical imaging procedures such as magnetic resonance imaging (MRI) and computed tomography (CT) scans to enhance the visibility of certain tissues or structures.

8. Biotechnology and Research: PEG is used in biotechnology and molecular biology for various purposes, including protein purification, cell fusion, and as a cryoprotectant for preserving biological samples.