Where peg is used?
Polyethylene glycol (PEG) is a biocompatible, synthetic, hydrophilic polyether compound that has many applications, mostly in the medical industry, but also in the chemical and industrial sectors. The structure of the compound is known as H−(O−CH2−CH2)n−OH.
Image Credit: StudioMolekuul/Shutterstock.com
The synthesis of PEG is done by polymerizing ethylene oxide, the main ingredient in antifreeze, using a ring-opening technique, which allows for PEGs of a range of molecular weights and molecular weight distributions to be constructed. This range in weights is what makes it suitable for several uses.
While varying the molecular weight of PEG can have slight effects on its characteristics, mostly on its shape and physical appearance, many characteristics define PEG. It is non-toxic, colorless, inert, odorless, and non-volatile. Also, it is incredibly soluble in water, and organic solvents such as benzene, carbon tetrachloride, and chloroform.
Creating PEG substances of different molecular weights relies on constructing PEG with different length chains. Larger PEG molecules have a greater number of repetitions of their structure compared with smaller ones.
Below, we discuss how PEG is applied in the two main industries that it is active in.
PEG has a vast number of applications in the medical industry, and the list continues to grow. Due to its non-toxicity and high solubility, it lends itself to many pharmaceutical and biomedical applications.
To begin with, possibly the most common application of PEG in the medical industry is its use in laxatives. Because PEG can apply osmotic pressure, it can draw water into the waste matter, providing a laxative effect.
In a similar scenario, PEG is often utilized during whole bowel irrigations to prepare the gastrointestinal tract for investigation or surgery. PEG is also used in many pharmaceutical creams, ointments, and medical solvents.
Peptides, proteins, or oligonucleotides are used as drug targets for various illnesses. PEG can be used to bioconjugate itself to the target, by coupling itself with the target molecule to optimize the pharmacokinetic properties of drug treatment.
PEG can be used as an inactive substance that acts as the vehicle for a drug. The process of drug delivery relies heavily on PEG because the compound can link together antibody-drug conjugates (ADCs). It can also be used to improve systematic drug delivery by adding it as a surface coating on nanoparticles. PEG can also be used to slow the clearance of coated proteins from the blood in biomedicines.
PEG hydrogels are also used in drug delivery, as well as in tissue engineering. PEG hydrogels are polymer networks that are created by crosslinking reactive PEG end groups, resulting in gels that are resistant to protein biodegradation and adhesion. These properties are beneficial to tissue engineering and drug delivery.
In vitro assays have also become dependent on PEG, using it to mimic crowded cellular conditions to allow researchers to research intracellular environments outside of the body.
Protein analysis is another biomedical area that utilizes PEG, which is used in several applications in this field. The compound is used as a precipitant for DNA isolation as well as for cell crystallization, helping to reveal the atomic structure of proteins.
Gene therapy uses PEG to coat vectors, for example, viruses, to protect them from being inactivated by the immune system, and to de-target them in the organs, preventing their potentially toxic effect.
PEG is also particularly essential in blood banks, where it is used to enhance the salience of antibodies and antigens.
The future is likely to see more medical applications of PEG develop. One current focus of research in this area is exploring how PEG can be used in the spinal cord and peripheral nerve injury, by employing it to fuse axons that have been compromised.
PEG has many roles in the chemical industry, which also cross over into applications in other industries. Firstly, it is well known for its use as a binding and dispersing agent, as it can improve the separation of particles and prevent clumping.
Also, as PEG has hydrophilic properties, it has found a role in preventing the non-specific sticking of proteins in studies using single-molecule fluorescence.
Also, because the compound is non-toxic and recognized as safe by the FDA, it has been able to be used in numerous coatings that enable lubrication in various scenarios.
Applications in preservation have also found a use for PEG, which is now employed to prevent and slow the damage and shrinkage of wood that has been submerged. It was used to preserve the Vasa warship in Stockholm, replacing the water trapped within the wood to prevent warping and shrinking.
Another famous case that has appropriated PEG is the restoration and preservation of the Terracotta Warriors. A PEG preservative was specially developed to preserve the colors painted onto the Terracotta army, which date back to the Qin Shi Huang Di dynasty.
As in the medical industry, the chemical applications of PEG will likely continue to grow.
Polyethylene glycol (PEG) is found in many skin creams, lotions, soaps, hair products and shower gels. PEGs are petroleum-based compound that are often used as thickeners, solvents, softeners, and moisture-carriers. they have three main uses in cosmetics: as an emollient to help soften and moisturise the skin, as an emulsifiers to help oil and water-based ingredients mix together properly), and as a carrier that can help deliver other ingredients deeper into the skin.
In the ingredients list of a product it’s usually called PEG followed by a number e.g. PEG-400 or PEG 8000. This is because PEG is in fact a long chain of smaller ethylene glycol molecules stuck together. The number following PEG can either stand for how heavy the molecule is or how many ethylene glycol units make up the larger chain.
These ingredients are also used in many ways outside of cosmetics including medicine, food and some manufacturing processes. Different sizes are better at different jobs, in cosmetics you might use PEG 400 up to 8000 but they can go as high as PEG 180,000.
While PEGs are not so popular with consumers (see safety), they are popular with manufacturers as they make a great base for cosmetic products. They are soluble in water and can help less soluble ingredient dissolve as well. This means active ingredients that usually need to be in an oil based product can instead be used in an aqueous or water-based product. Their water binding potential gives the product a non-greasy, non-sticky texture and also acts as a humectant or moisturiser, actively holding onto the water it binds, stopping the product from drying out on your skin.
In soaps, hair products and shower gels, they act as plasticisers which lower the brittleness of the products and give it a silkier feeling.
Because things like melting point, viscosity and water retaining ability vary with the PEG’s size, a mix of different sizes can be used in one product to give the desired effect.
Side effects:
PEGs are unlikely to cause irritation or sensitisation of the skin unless the skin is damaged. As such it’s recommended that you avoid applying products containing these ingredients to broken or damaged skin.
Contamination of PEGs with the carcinogenic molecules ethylene oxide and 1,4-dioxane may occur as a by-product of PEG production, depending on the producer. While these molecules are dangerous, they are typically found in far too low a concentration to cause adverse effects according to an Environment Canada investigation.
Some studies have shown that they can carry unwanted substances across the skin barrier as well, especially if the skin barrier is compromised by a skin condition like eczema or injured.
Interactions with other medicine:
Some sizes of PEG can act as a penetration enhancer, increases the ability of certain molecules to cross the skin barrier and increasing the dosage received.
In general however PEGs in cosmetics are considered safe to use.
Other names for PEG:
PEG-4, PEG-6, PEG-7, PEG-8, PEG-9, PEG-10, PEG-12, PEG-14, PEG-16, PEG-18, PEG-20, PEG-32, PEG-33, PEG-40, PEG-45, PEG-55, PEG-60, PEG-75, PEG-80, PEG-90, PEG-100, PEG-135, PEG-150, PEG-180, PEG-200, PEG-220, PEG-240, PEG-350, PEG-400, PEG-500, PEG-800, PEG-2M, PEG-5M, PEG-7M, PEG-9M, PEG-14M, PEG-20M, PEG-23M, PEG-25M, PEG-45M, PEG-65M, PEG-90M, PEG-115M, PEG-160M, PEG-180M, Poly(oxyethylene), Carbowax, GoLYTELY, GlycoLax, Fortrans, TriLyte, Colyte, Halflytely, Macrogol, MiraLAX, MoviPrep
Polyethylene glycol (PEG) is found in many skin creams, lotions, soaps, hair products and shower gels. PEGs are petroleum-based compound that are often used as thickeners, solvents, softeners, and moisture-carriers. they have three main uses in cosmetics: as an emollient to help soften and moisturise the skin, as an emulsifiers to help oil and water-based ingredients mix together properly), and as a carrier that can help deliver other ingredients deeper into the skin.
In the ingredients list of a product it’s usually called PEG followed by a number e.g. PEG-400 or PEG 8000. This is because PEG is in fact a long chain of smaller ethylene glycol molecules stuck together. The number following PEG can either stand for how heavy the molecule is or how many ethylene glycol units make up the larger chain.
These ingredients are also used in many ways outside of cosmetics including medicine, food and some manufacturing processes. Different sizes are better at different jobs, in cosmetics you might use PEG 400 up to 8000 but they can go as high as PEG 180,000.
While PEGs are not so popular with consumers (see safety), they are popular with manufacturers as they make a great base for cosmetic products. They are soluble in water and can help less soluble ingredient dissolve as well. This means active ingredients that usually need to be in an oil based product can instead be used in an aqueous or water-based product. Their water binding potential gives the product a non-greasy, non-sticky texture and also acts as a humectant or moisturiser, actively holding onto the water it binds, stopping the product from drying out on your skin.
In soaps, hair products and shower gels, they act as plasticisers which lower the brittleness of the products and give it a silkier feeling.
Because things like melting point, viscosity and water retaining ability vary with the PEG’s size, a mix of different sizes can be used in one product to give the desired effect.
Side effects:
PEGs are unlikely to cause irritation or sensitisation of the skin unless the skin is damaged. As such it’s recommended that you avoid applying products containing these ingredients to broken or damaged skin.
Contamination of PEGs with the carcinogenic molecules ethylene oxide and 1,4-dioxane may occur as a by-product of PEG production, depending on the producer. While these molecules are dangerous, they are typically found in far too low a concentration to cause adverse effects according to an Environment Canada investigation.
Some studies have shown that they can carry unwanted substances across the skin barrier as well, especially if the skin barrier is compromised by a skin condition like eczema or injured.
Interactions with other medicine:
Some sizes of PEG can act as a penetration enhancer, increases the ability of certain molecules to cross the skin barrier and increasing the dosage received.
In general however PEGs in cosmetics are considered safe to use.
Other names for PEG:
Polyethylene glycol (PEG; /ˌpɒliˈɛθəlˌiːn ˈɡlaɪˌkɒl, -ˈɛθɪl-, -ˌkɔːl/) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular weight. The structure of PEG is commonly expressed as H−(O−CH2−CH2)n−OH.[3]
PEG is considered biologically inert and safe by the FDA.
However, a growing body of evidence shows the existence of a detectable level of anti-PEG antibodies in approximately 72% of the population, never treated with PEGylated drugs, based on plasma samples from 1990 to 1999.[43][further explanation needed] Due to its ubiquity in a multitude of products and the large percentage of the population with antibodies to PEG, hypersensitive reactions to PEG are an increasing concern.[44][45] Allergy to PEG is usually discovered after a person has been diagnosed with an allergy to an increasing number of seemingly unrelated products, including processed foods, cosmetics, drugs, and other substances that contain PEG or were manufactured with PEG.[44]
PEG, PEO, and POE refer to an oligomer or polymer of ethylene oxide. The three names are chemically synonymous, but historically PEG is preferred in the biomedical field, whereas PEO is more prevalent in the field of polymer chemistry. Because different applications require different polymer chain lengths, PEG has tended to refer to oligomers and polymers with a molecular mass below 20,000 g/mol, PEO to polymers with a molecular mass above 20,000 g/mol, and POE to a polymer of any molecular mass.[46] PEGs are prepared by polymerization of ethylene oxide and are commercially available over a wide range of molecular weights from 300 g/mol to 10,000,000 g/mol.[47]
PEG and PEO are liquids or low-melting solids, depending on their molecular weights. While PEG and PEO with different molecular weights find use in different applications, and have different physical properties (e.g. viscosity) due to chain length effects, their chemical properties are nearly identical. Different forms of PEG are also available, depending on the initiator used for the polymerization process – the most common initiator is a monofunctional methyl ether PEG, or methoxypoly(ethylene glycol), abbreviated mPEG. Lower-molecular-weight PEGs are also available as purer oligomers, referred to as monodisperse, uniform, or discrete. Very high-purity PEG has recently been shown to be crystalline, allowing determination of a crystal structure by x-ray crystallography.[47] Since purification and separation of pure oligomers is difficult, the price for this type of quality is often 10–1000 fold that of polydisperse PEG.
PEGs are also available with different geometries.
The numbers that are often included in the names of PEGs indicate their average molecular weights (e.g. a PEG with n = 9 would have an average molecular weight of approximately 400 daltons, and would be labeled PEG 400). Most PEGs include molecules with a distribution of molecular weights (i.e. they are polydisperse). The size distribution can be characterized statistically by its weight average molecular weight (Mw) and its number average molecular weight (Mn), the ratio of which is called the polydispersity index (ĐM). Mw and Mn can be measured by mass spectrometry.
PEGylation is the act of covalently coupling a PEG structure to another larger molecule, for example, a therapeutic protein, which is then referred to as a PEGylated protein. PEGylated interferon alfa-2a or alfa-2b are commonly used injectable treatments for hepatitis C infection.
PEG is soluble in water, methanol, ethanol, acetonitrile, benzene, and dichloromethane, and is insoluble in diethyl ether and hexane. It is coupled to hydrophobic molecules to produce non-ionic surfactants.[48]
PEGs potentially contain toxic impurities, such as ethylene oxide and 1,4-dioxane.[49] Ethylene glycol and its ethers are nephrotoxic if applied to damaged skin.[50]
PEG and related polymers (PEG phospholipid constructs) are often sonicated when used in biomedical applications. However, as reported by Murali et al., PEG is very sensitive to sonolytic degradation and PEG degradation products can be toxic to mammalian cells. It is, thus, imperative to assess potential PEG degradation to ensure that the final material does not contain undocumented contaminants that can introduce artifacts into experimental results.[51]
PEGs and methoxypolyethylene glycols are manufactured by Dow Chemical under the trade name Carbowax for industrial use, and Carbowax Sentry for food and pharmaceutical use. They vary in consistency from liquid to solid, depending on the molecular weight, as indicated by a number following the name. They are used commercially in numerous applications, including foods, in cosmetics, in pharmaceutics, in biomedicine, as dispersing agents, as solvents, in ointments, in suppository bases, as tablet excipients, and as laxatives. Some specific groups are lauromacrogols, nonoxynols, octoxynols, and poloxamers.
Macrogol (with brand names such as Laxido, GoLytely and Miralax) is the generic name for polyethylene glycol used as a laxative. The name may be followed by a number which represents the average molecular weight (e.g. macrogol 3350, macrogol 4000 or macrogol 6000).
The production of polyethylene glycol was first reported in 1859. Both A. V. Lourenço and Charles Adolphe Wurtz independently isolated products that were polyethylene glycols.[52] Polyethylene glycol is produced by the interaction of ethylene oxide with water, ethylene glycol, or ethylene glycol oligomers.[53] The reaction is catalyzed by acidic or basic catalysts. Ethylene glycol and its oligomers are preferable as a starting material instead of water, because they allow the creation of polymers with a low polydispersity (narrow molecular weight distribution). Polymer chain length depends on the ratio of reactants.
Depending on the catalyst type, the mechanism of polymerization can be cationic or anionic. The anionic mechanism is preferable because it allows one to obtain PEG with a low polydispersity. Polymerization of ethylene oxide is an exothermic process. Overheating or contaminating ethylene oxide with catalysts such as alkalis or metal oxides can lead to runaway polymerization, which can end in an explosion after a few hours.
Polyethylene oxide, or high-molecular-weight polyethylene glycol, is synthesized by suspension polymerization. It is necessary to hold the growing polymer chain in solution in the course of the polycondensation process. The reaction is catalyzed by magnesium-, aluminium-, or calcium-organoelement compounds. To prevent coagulation of polymer chains from solution, chelating additives such as dimethylglyoxime are used.
Alkaline catalysts such as sodium hydroxide (NaOH), potassium hydroxide (KOH), or sodium carbonate (Na2CO3) are used to prepare low-molecular-weight polyethylene glycol.[54]
Like most polyethers, polyethylene glycol is made by polymerising (combining with) monomers. It does this by forming ether links between them, which have a chain-like molecular structure.
In the case of PEG, ethylene oxide is reacted with ethylene glycol. An acidic or basic catalyst is then used to catalyse the reaction. When ethylene glycol polymerises, the reaction creates a variety of products. Each of these contain a different number of ethylene glycol units and are referred to as PEGs.
PEG refers to an extremely diverse range of polyethers that are available in a variety of molecular weights. The characteristics of polyethylene glycol are similarly varied as its appearance is respective to its molecular weight. In general, polyethylene glycol is:
Polyethylene glycol is also extremely soluble in water and most organic solvents, like benzene, chloroform and carbon tetrachloride. The physical appearance of PEG changes depending on its molecular weight:
In terms of chemistry, the difference between low and high molecular PEG weights is the length of their chains.
For example, PEG 400 means that there is an average weight of 400 daltons. This means that there are approximately 9 ether repetitions that form the polyethylene glycol molecule. PEG 4000, on the other hand, will have a considerably longer chain because it will have more ether repetitions in its structure.
Its non-toxic properties, solubility and ability to be rapidly removed make polyethylene glycol suited to a wide range of applications. It plays a huge role in medical and pharmaceutical industries, but is also used in everything from food processing and polyutherane manufacturing to cleaners and detergents. Here are 5 of its most notable applications:
The most common medical use of polyethylene glycol is as a laxative. This is because of its ability to use osmosis to pull water into the stool when inside the intestines. This softens the stool and makes it easier to pass. PEG’s capacity to apply osmotic pressure is also utilised in biochemistry tests.
Whole bowel irrigation is a medical process that is employed in order to empty the gastrointestinal tract. This is usually done before colonoscopies or bowel surgeries. PEG and added electrolytes are used during this process to help prepare the bowel.
PEG is used in many pharmaceutical applications because of its non-toxicity and high solubility. It is the basis of many skin creams and lubricants, where it is often combined with glycerin. It is also used in ointments, medical solvents and even fragrances.
Solid-grade PEG is the favourite when it comes to making film coatings for tablets. It behaves as an excellent plasticiser by preventing the coating film from rupturing or sustaining damage.
Polyethylene glycol is not only used as a lubricant in cosmetics. Low molecular weight PEG is used as an effective lubricant with printing ink, while most available types of PEG utilise their lubricant skills in the metal parts and textiles industries.
Polyethylene glycol is not only non-toxic but also non-corrosive. This means that it can be used with metals, plastics, rubbers and fabrics without causing any staining or damage. PEG can also be cleaned away very easily with water because of its high solubility.
Among PEGs many uses are its ability to function as a binding agent and dispersing agent across many industries. When manufacturing moulds in ceramics or casting, polyethylene glycol is used as a binding agent to ensure that the mould retains its shape and structure. As a dispersant, PEG improves the separation of particles in order to prevent clumping.
In toothpaste, polyethylene glycol acts as both a binding and dispersing agent by keeping the xanthan gum evenly distributed and preventing the paste from forming any clumps in the tube.
Polyethylene glycol is used in many more applications that span a variety of different industries. PEG is also used in:
While its cousin, ethylene glycol, is toxic to humans, PEG has been “recognised as safe” by the FDA and is classified as non-toxic. With that being said, polyethylene glycol does, like every chemical, have its drawbacks that should be kept in mind when using it directly.
The main issue surrounding PEGs toxicity is the fact that it contains ethylene glycol, a potential carcinogen and toxic substance. Depending on how it has been manufactured, PEG could also contain contaminants like lead, arsenic or 1,4-dioxane. Therefore, it is also worth doing your research before handling pure polyethylene glycol.
At ReAgent, our online chemical shop has polyethylene glycol available in a range of molecular weights. We also offer flexible packaging options to ensure that we meet the needs of your business. Check out our online shop today, or get in touch to find out more about what we can offer you.
Polyethylene glycols (PEGs) and their derivatives are widely used in cosmetics as surfactants, cleansing agents, emulsifiers, skin conditioners, and humectants. Adding to their use in cosmetics, many PEG compounds also have other applications.
