What is Polyethylene Glycol?

What is Polyethylene Glycol?

Published by BroadPharm on November 19, 2021

Polyethylene Glycol (PEG) is a synthetic polymer comprised of repeating units of ethylene oxide. PEG can be found in many applications of the medical industry as well as in the industrial, and commercial sectors.

What is PEG made of

Since the 1930s PEG has been made using anionic polymerization of ethoxides. PEG was subdivided into poly(ethylene) oxide (PEO) for molecular weights above 20,000 g/mol and PEG for lower weights. Because of the PEG acronym’s more common usage, some PEO compounds are also referred to as PEG in many parts of the chemical industry.

Figure 1 shows how synthesis occurs through polymerizing ethylene oxide using nucleophiles as initiators, which allows for PEGs of a range of molecular weights and molecular weight distributions to be constructed.

Diagram of peg production
Figure 1 . PEG production utilizes an alkaline catalyst, such as alkali metal compounds with high nucleophilicity, and a proton donating initiator like water or an alcohol in ethers (most often THF) or other polar, aprotic solvents represent the most popular initiator systems.

PEG polymer properties

PEG as a synthetic, water-soluble, and highly biocompatible material. PEG can be classified as Monodispersed PEG and Polydispersed PEG (poly PEG), as well as PEO for polymers with over 20,000 molecular weights. PEG polymers can include many shapes such as linear, branched, and star, with a combination of different PEG chain lengths. PEG is characterized as non-toxic, inert, colorless, odorless, and non-volatile. It is very soluble in water and organic solvents such as benzene, carbon tetrachloride, and chloroform. However, PEG is insoluble in diethyl ether and hexane.

What is PEG used for

PEG has been shown to be useful in medicine both on its own as well as in modifying biomolecules, nanocarriers, surfaces, and drugs.

One of the most common applications of PEG in medicine is as a laxative, generally labeled as Macrogol. PEG can have a laxative effect when ingested because the polymer draws water into the waste matter due to osmotic pressure.

Another application is in blood banks that use PEG, in a low ionic strength saline solution, to remove water from the system and thus concentrates the antibodies present.

PEGylated materials tend to have a low protein-affinity, which can allow for prolonged body-circulation times with low immunogenicity. This may be due to the polymer chain’s steric hindrance and surface hydration, which creates an antifouling effect for PEG coatings. When PEG chains are crosslinked with each other PEG hydrogels can be created for use in drug delivery and tissue engineering. These polymer networks are resistant to adhesion and degradation by proteins.

These properties can also be useful in some selective protein capture research. An example of this is combating hemophilia by selectively bind coagulation factor VIII, which significantly reduce bleeding times in animal tests.

Because of the hydrophilic properties mentioned earlier, PEG has been shown to be useful in preventing the non-specific sticking of proteins during single-molecule fluorescence studies.

Finally, due to the inert and non-toxic nature of PEG compounds there are many applications that utilize PEG as a filler in paints and lubrication. They are also well known for their use as binding and dispersing agents since PEG can prevent clumping and improve the separation of particles.

peg polymer as an ingredient in pharmaceuticals
Figure 2 . PEG polymer is a critical ingredient in pharmaceuticals, chemical, biological, industrial, commercial, and recreational uses.

PEG Modified Drugs

PEGylation of protein drugs to can improve the results for patients. One example of this is Adagen, which is comprised of the protein Adenosine Deaminase that has 11-17 PEG 5K chains. Increasing the drug's size prevents it from renal clearance and extends the lifetime of the drug. This also enhanced solubility and decreases the accessibility for proteolytic enzymes and antibodies.

PEGylated Small molecule drugs have also been shown to increase solubility and target-specificity, as exemplified by Diprivan (Propofol). Diprivan incorporates an m-PEG10 entity into the drug to enhance stability in the bloodstream and sustained release at physiological pH.

PEG Modified Delivery Systems

PEG has also been used in several successful applications as a linker to develop targeting drug delivery systems. >One example of this is the development Antibody-Drug Conjugates (ADCs) for the treatment of various types of cancer. ADCs composed of a drug linked to an mAbs (antibody) that is designed to specifically release their payload at a tumor. Since 2000, the FDA has approved 11 different ADCs.

Another example of PEG used in delivery systems is liposome encapsulated (LNP) drugs that rely on PEGylated lipids. LNPs are a critical technology for developing mRNA-based drugs, such as the Pfizer and Moderna COVID-19 vaccines. PEGylated lipids are important in LNPs for optimization of particle size, stabilization, and can be useful for further modification to improve targeted delivery. PEG2000-DMG (Moderna) and PEG2000-DSG (Pfizer) are two examples of PEGylated lipids that are internal components of LNPs.

PEG Used in Fluorescent Tagging

Fluorescent tags, a.k.a. labels or probes, are critical chemical compounds for studying biomolecules such as a proteins, antibodies, and amino acids in larger systems. Fluorescent tags work by emitting specific wavelengths when exited by laser excitation. By adding PEG spacers, the tags become more water solubility and efficient in biolabeling. One area of interest is being able to remotely monitor the pH at the surface of a cell during various biological processes. Figure 3 shows an example of a ratio metric analysis of cell surfaces to determine their relative pH levels using a FITC-PEG-lipid. The study used excitation wavelengths of 458nm and 488nm, the fluorescence was detected at 500–550nm.

confocal laser scan images
Figure 3 . Confocal laser scanning microscopy images and chart taken from Ohgaki, R., et. al., (a) Pseudo colored fluorescence ratio images (Ex 488nm/458nm) acquired during the stepwise external pH shift from pH 7.5 to 5.0. Scale bars: 20μm. (b) Plot of the fluorescence ratio in ROIs against the pH of external buffers.

PEGylation Regents Supplier

BroadPharm is a leading supplier of PEGylation reagents, including high purity monodisperse PEG and Polymer PEG to empower our customer’s advanced research worldwide. These compounds feature great aqueous solubility, wide range of polymer length/weight, and a broad selection of all the popular PEGylation functional groups. Please visit our product page for all our in-stock PEGylation reagents.

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