PEG 600

Composition

Polyethylene glycol
H(OCH2CH2)nOH
n = about 13
CAS-No.: 25322-68-3
INCI-designation: PEG-12
CAS # 25322-68-3

Synonyms:
 
polyethylene glycol 600
polyoxyethylene 600
PEG 600
Polyglykol 600

PEG 600 is PEG-12-based plasticizer and mold release agent. 
Polyethylene Glycol (PEG) 600 possesses lubricity and humectant properties. 
Polyethylene Glycol 600 maintains wet-tack strength. 
Polyethylene Glycol 600 is used in pressure sensitive and thermoplastic adhesives.

Product properties*)
Polyglykol 600 is clear viscous liquid at room temperature.
Polyglykol 600 can be supplied in tank trucks or in steel drums. 
Its two hydroxy end groups as well as its ether groups mainly control the physical and chemical properties of Polyglykol 600. 
Therefore Polyglykol 600 is soluble in water and polar organic solvents like aceton or methanol. 
Polyglykol 600 is insoluble in pure hydrocarbons. 
Polyglykol 600 displays typical chemical reactions of alcohols/diols.
The solidification point, of Polyglykol 600 is about 20°C. 
Besides standard grade Polyglykol 600 special qualities Polyglykol 600 PU and Polyglykol 600 A with low sodium concentrations and/or low water concentrations are available on request.

Storage
When stored in a cold, dry place in a closed container Polyglykol 600 can be kept for at least two years.

Applications
Based on their physical and chemical characteristics polyethylene glycols are used for a wide variety of applications.

Fields of applications:
PEG 600 is used as Reactive diol/polyether component in polyester or polyurethene resins
PEG 600 is a component of auxiliaries for leather and textile processing
PEG 600 is used in Cosmetic / pharmaceutical formulations (e.g. humectant or solubilizer for creams, shampoos, tooth paste and injection fluids)
PEG 600 is a Lubricant and mould release agent for rubber and elastomer processing
PEG 600 Plasticizer and binder for ceramic and concrete manufacturing
PEG 600 is a Component of lubricant formulations
PEG 600 is Water soluble, lubricating component in metal working fluids


Storage
When stored in a cold, dry place in a closed container Polyglykol 600 can be kept for at least two years.

Applications
Based on their physical and chemical characteristics polyethylene glycol 600 are used for a wide variety of applications.

Fields of applications:
- Reactive diol/polyether component in polyester or polyurethene resins
- Component of auxiliaries for leather and textile processing
- Cosmetic / pharmaceutical formulations (e.g. humectant or solubilizer for creams, shampoos, tooth paste and injection fluids)
- Lubricant and mould release agent for rubber and elastomer processing
- Plasticizer and binder for ceramic and concrete manufacturing
- Component of lubricant formulations
- Water soluble, lubricating component in metal working fluids
- Humectant for paper, wood and cellulose films
- Solvent and humectant for dyes and inks
- Modifier for production of regenerated viscose
- Humectant and plasticizer for adhesives
- Heat transfer medium


Polyethylene Glycol 600
Product CAS # 25322-68-3
Description Polyethylene Glycol
Applications Adhesives
Antistatic Agent and Humectant
Chemical Intermediates
Inks
Lubricants
Mold Release Agent
Plasticizer
Wood Treatment


Property
Value
Physical Form : Liquid to Semisolid
Average Number of Repeating Oxyethylene Units: 13.2
Range of Average Molecular Weight: 570 – 630
Range of Average Hydroxyl Number, mg KOH/g 178 – 197
Density, g/cm3 at 20°C: 1.126
Melting or Freezing Range, °C : 15 – 25
Solubility in Water at 20°C, % by weight: Complete
Viscosity at 100°C, cSt :10.8
Heat of Fusion, Cal/g :35


Appearance at 25ºC: liquid        

Transparence at 20ºC: clear        

pH value: 5.0 - 7.0         
(5% in water)

Free 1.4 Dioxane: max. 1.0 ppm    

Apha colour at 25°C: max. 15.0 (25% in water)

Water content: max. 0.5    % (Karl-Fischer)

Hydroxyl value: 178.0 - 197.0    mgKOH/g    

Free ethylene oxide: max. 10.0    ppm    

Molecular weight: 570.0 - 630.0    g/mol    

Viscosity at 98.9ºC: 9.90 - 11.30 cSt    


Uses
Medical uses
Main articles: Macrogol and PEG 600ylation
PEG 600 is the basis of a number of laxatives (as MiraLax).
Whole bowel irrigation with polyethylene glycol and added electrolytes is used for bowel preparation before surgery or colonoscopy.
PEG 600 is also used as an excipient in many pharmaceutical products.
PEG 600 used in medicines for treating disimpaction and maintenance therapy for children with constipation.
When attached to various protein medications, polyethylene glycol allows a slowed clearance of the carried protein from the blood.
The possibility that PEG 600 could be used to fuse axons is being explored by researchers studying peripheral nerve and spinal cord injury.
An example of PEG 600 hydrogels (see "Biological uses" section) in a therapeutic has been theorized by Ma et al. 
They propose using the hydrogel to address periodontitis (gum disease) by encapsulating stem cells in the gel that promote healing in the gums.
The gel and encapsulated stem cells was to be injected to the site of disease and crosslinked to create the microenvironment required for the stem cells to function.


Because PEG 600 is a hydrophilic molecule, it has been used to passivate microscope glass slides for avoiding non-specific sticking of proteins in single-molecule fluorescence studies.

Polyethylene glycol has a low toxicity and is used in a variety of products.
The polymer is used as a lubricating coating for various surfaces in aqueous and non-aqueous environments.
Since PEG 600 is a flexible, water-soluble polymer, it can be used to create very high osmotic pressures (on the order of tens of atmospheres). 
It also is unlikely to have specific interactions with biological chemicals. 
These properties make PEG 600 one of the most useful molecules for applying osmotic pressure in biochemistry and biomembranes experiments, in particular when using the osmotic stress technique.
Polyethylene glycol is also commonly used as a polar stationary phase for gas chromatography, as well as a heat transfer fluid in electronic testers.

PEG 600 has also been used to preserve wooden and in some cases other organic objects that have been salvaged from underwater archaeological contexts, as was the case with the warship Vasa in Stockholm,[15] and similar cases. It replaces water in wooden objects, making the wood dimensionally stable and preventing warping or shrinking of the wood when it dries.[4] In addition, PEG 600 is used when working with green wood as a stabilizer, and to prevent shrinkage.[16]
PEG 600 has been used to preserve the painted colors on Terracotta Warriors unearthed at a UNESCO World Heritage site in China.
These painted artifacts were created during the Qin Shi Huang (first emperor of China) era. 

PEG 600 is often used (as an internal calibration compound) in mass spectrometry experiments, with its characteristic fragmentation pattern allowing accurate and reproducible tuning.
PEG 600 derivatives, such as narrow range ethoxylates, are used as surfactants.
PEG 600 has been used as the hydrophilic block of amphiphilic block copolymers used to create some polymersomes.

Biological uses

An example study was done using PEG 600-Diacrylate hydrogels to recreate vascular environments with the encapsulation of endothelial cells and macrophages. This model furthered vascular disease modeling and isolated macrophage phenotype's effect on blood vessels.
PEG 600 is commonly used as a crowding agent in in vitro assays to mimic highly crowded cellular conditions.
PEG 600 is commonly used as a precipitant for plasmid DNA isolation and protein crystallization. 
X-ray diffraction of protein crystals can reveal the atomic structure of the proteins.
PEG 600 is used to fuse two different types of cells, most often B-cells and myelomas in order to create hybridomas. 

In blood banking, PEG 600 is used as a potentiator to enhance detection of antigens and antibodies.

In biophysics, polyethylene glycols are the molecules of choice for the functioning ion channels diameter studies, because in aqueous solutions they have a spherical shape and can block ion channel conductance.
Commercial uses
PEG 600 is the basis of many skin creams (as cetomacrogol) and personal lubricants (frequently combined with glycerin).
PEG 600 is used in a number of toothpastes as a dispersant. In this application, it binds water and helps keep xanthan gum uniformly distributed throughout the toothpaste.
PEG 600 is also under investigation for use in body armor, and in tattoos to monitor diabetes.
In low-molecular-weight formulations (e.g. PEG 600 400), it is used in Hewlett-Packard designjet printers as an ink solvent and lubricant for the print heads.
PEG 600 is also used as an anti-foaming agent in food and drinks– its INS number is 1521 or E1521 in the EU.

Industrial uses

PEG 600 has been used as the gate insulator in an electric double-layer transistor to induce superconductivity in an insulator.[37]
PEG 600 is also used as a polymer host for solid polymer electrolytes. Although not yet in commercial production, many groups around the globe are engaged in research on solid polymer electrolytes involving PEG 600, with the aim of improving their properties, and in permitting their use in batteries, electro-chromic display systems, and other products in the future.
PEG 600 is injected into industrial processes to reduce foaming in separation equipment.
PEG 600 is used as a binder in the preparation of technical ceramics.[38]

Recreational uses
PEG 600 is used to extend the size and durability of very large soap bubbles.
PEG 600 is the main ingredient in many personal lubricants. (Not to be confused with propylene glycol.)
PEG 600 is the main ingredient in the paint (known as "fill") in paintballs.

Health effects
PEG 600 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 600 antibodies in approximately 72% of the population, never treated with PEG 600ylated drugs, based on plasma samples from 1990–1999.[39] Due to its ubiquity in a multitude of products and the large percentage of the population with antibodies to PEG 600, hypersensitive reactions to PEG 600 are an increasing concern.[40][41] Allergy to PEG 600 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 600 or were manufactured with PEG 600.[40]

Available forms and nomenclature
PEG 600, PEO, and POE refer to an oligomer or polymer of ethylene oxide. The three names are chemically synonymous, but historically PEG 600 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 600 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.[42] PEG 600s 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.[43]

PEG 600 and PEO are liquids or low-melting solids, depending on their molecular weights. While PEG 600 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 600 are also available, depending on the initiator used for the polymerization process – the most common initiator is a monofunctional methyl ether PEG 600, or methoxypoly(ethylene glycol), abbreviated mPEG 600. Lower-molecular-weight PEG 600s are also available as purer oligomers, referred to as monodisperse, uniform, or discrete. Very high-purity PEG 600 has recently been shown to be crystalline, allowing determination of a crystal structure by x-ray crystallography.[43] 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 600.

PEG 600s are also available with different geometries.

Branched PEG 600s have three to ten PEG 600 chains emanating from a central core group.
Star PEG 600s have 10 to 100 PEG 600 chains emanating from a central core group.
Comb PEG 600s have multiple PEG 600 chains normally grafted onto a polymer backbone.
The numbers that are often included in the names of PEG 600s indicate their average molecular weights (e.g. a PEG 600 with n = 9 would have an average molecular weight of approximately 400 daltons, and would be labeled PEG 600 400). Most PEG 600s 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.

PEG 600ylation is the act of covalently coupling a PEG 600 structure to another larger molecule, for example, a therapeutic protein, which is then referred to as a PEG 600ylated protein. PEG 600ylated interferon alfa-2a or alfa-2b are commonly used injectable treatments for hepatitis C infection.

PEG 600 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.[44]

PEG 600s potentially contain toxic impurities, such as ethylene oxide and 1,4-dioxane.
Ethylene glycol and its ethers are nephrotoxic if applied to damaged skin.


Polyethylene oxide (PEO, Mw 4 kDa) nanometric crystallites (4 nm)
PEG 600 and related polymers (PEG 600 phospholipid constructs) are often sonicated when used in biomedical applications. However, as reported by Murali et al., PEG 600 is very sensitive to sonolytic degradation and PEG 600 degradation products can be toxic to mammalian cells. It is, thus, imperative to assess potential PEG 600 degradation to ensure that the final material does not contain undocumented contaminants that can introduce artifacts into experimental results.[47]

PEG 600s 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, MiraLax, GoLytely, Colace used as a laxative, is a form of polyethylene glycol. The name may be followed by a number which represents the average molecular weight (e.g. macrogol 3350, macrogol 4000 or macrogol 6000).

Production

Polyethylene glycol 600, pharmaceutical quality

The production of polyethylene glycol was first reported in 1859. 
 Polyethylene glycol is produced by the interaction of ethylene oxide with water, ethylene glycol, or ethylene glycol oligomers.
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.

HOCH2CH2OH + n(CH2CH2O) → HO(CH2CH2O)n+1H
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 600 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.

PEG 600

Polyethylene glycol  is a polyether compound 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.

Chemical uses
Polyethylene glycol 600 has a low toxicity and is used in a variety of products. The polymer is used as a lubricating coating for various surfaces in aqueous and non-aqueous environments.
Since PEG is a flexible, water-soluble polymer, it can be used to create very high osmotic pressures (on the order of tens of atmospheres). It also is unlikely to have specific interactions with biological chemicals. These properties make PEG one of the most useful molecules for applying osmotic pressure in biochemistry and biomembranes experiments, in particular when using the osmotic stress technique.
Polyethylene glycol is also commonly used as a polar stationary phase for gas chromatography, as well as a heat transfer fluid in electronic testers.
PEG 600 has also been used to preserve objects that have been salvaged from underwater, as was the case with the warship Vasa in Stockholm, and similar cases. It replaces water in wooden objects, making the wood dimensionally stable and preventing warping or shrinking of the wood when it dries. In addition, PEG is used when working with green wood as a stabilizer, and to prevent shrinkage.
PEG 600 has been used to preserve the painted colors on Terracotta Warriors unearthed at a UNESCO World Heritage site in China. These painted artifacts were created during the Qin Shi Huang Di dynasty (first emperor of China). Within 15 seconds of the terra-cotta pieces being unearthed during excavations, the lacquer beneath the paint begins to curl after being exposed to the dry Xian air. The paint would subsequently flake off in about four minutes. The German Bavarian State Conservation Office developed a PEG preservative that when immediately applied to unearthed artifacts has aided in preserving the colors painted on the pieces of clay soldiers.
PEG is often used (as an internal calibration compound) in mass spectrometry experiments, with its characteristic fragmentation pattern allowing accurate and reproducible tuning.


Polyethylene glycol
Poly(ethylene glycol)
Polyethylene glycol
polyethylene oxide standard 511000
Poly(ethylene oxide)
macrogol
poly(oxyethylene)
Polyethylene glycol PEG
Aquacide III
PEG 1000
PEG 6000, MB Grade (1.12033)
Ethylene glycol 8000 polymer
Polyethyleneglycol
Polyethylene Glycol 5000000
PolyethyleneoxideMW
PEG 200-8000
Tri-(2,3-Dibromopropyl) Phosphate
Polyethylene glycol - 6000 grade
PEG 200
PEG 400
PEG 6000
Poly(ethylene oxide)
PEO
PEG 600
Polyethyleneoxidemonomethacryloxymonotrimethylsiloxyterminated
O-Methacryloxy(polyethyleneoxy)trimethylsilane
PEG
Poly ethylene glycol
Carmowax
carbowax
PEG 8000
Polyethylene glycol series
Polyethylene Glycol
Polyethylene glygcol

Polyethylene glycols, also called macrogols in the European pharmaceutical industry, are manufactured by polymerization of ethylene oxide (EO) with either water, mono ethylene glycol or diethylene glycol as starting material, under alkaline catalysis. 
After the desired molecular weight is reached (usually checked by viscosity measurements as in-process control) the reaction is terminated by neutralizing the catalyst with acid.
Normally lactic acid is used, but also acetic acid or others can also be used.
The result is a very simple chemical structure: HO-[CH2-CH2-O]n-H, where (n) is the number of EO-units.


Although technically these products should be called polyethylene oxides, for products with mean molecular weights of 200 to 35000, the term polyethylene glycols is normally used to indicate the signifi cant infl uence of the hydroxyl end groups on the chemical and physical properties of these molecules. 
Only products made by polymerization of ethylene oxide in solvents, with molecular weights up to several millions, are called polyethylene oxides.
As an abbreviation for polyglycols, the term “PEG” is used, in combination with a numerical value. 
Within the pharmaceutical industry, the number indicates the mean molecular weight, whereas in the cosmetic industry the number refers to the number (n) of EO-units in the molecule. 
Since the molecular weight of ethylene oxide is 44, the average molecular weight values of PEGs are given as round values of n*44.
Unfortunately, the various pharmacopoeias use different nomenclature for some PEG molecular weights. 
The table lists in additional to the European, US and Japanese monographs, also the nomenclature of the British Pharmacopoeia II from 1993. 
Even though this monograph is no longer valid, the nomenclature is still often used today.

Polyethylene glycols with a mean molecular weight up to 400 are non-volatile liquids at room temperature. 
PEG 600 shows a melting range of about 17 to 22°C, so it may be liquid at room temperature but pasty at lower ambient temperatures, while PEGs with 800 to 2000 mean molecular weight are pasty materials with a low melting range. 
Above a molecular weight of 3000, the polyethylene glycols are solids and are available not only in flaked form but also as powder. 
Polyglykols up to a molecular weight of 35000 are commercially available. 
The hardness of Polyglykols increases with increasing molecular weight, however the melting range goes up to a maximum value of about 60°C.

The most important property of all PEGs is their solubility in water, making them ideally suited for use in countless different applications.
Liquid PEGs up to PEG 600 are miscible with water in any ratio. 
But even solid PEG grades have excellent solubility in water. 
Although it falls slightly with increasing molar mass, even 50% (w / w) of a PEG 35000 can be dissolved. 
The solubility and viscosity of the solutions is not affected by the presence of electrolytes, since PEGs are nonionic substances.
PEGs are quite soluble in hard water or in other aqueous solutions of various salts.
Some physical and chemical properties are described in more detail in the following chapters.


The surface tension of the liquid PEGs 200 to 600 is about 47 mN/m at room temperature.
There is only a slight difference in the surface tension of liquid and solid PEGs in aqueous solutions; a 10% solution of PEG 400 has a value of 64 mN/m, while a 10% solution of PEG 4000 has a value of about 60 mN/m at 20°C.
PEGs possess no characteristic surfaceactive properties and can therefore not be included in the class surfactants. 
Nevertheless, they frequently prove to be useful dispersing agents or solubilizers. 
It is not possible to give an HLB value for PEGs.


SOLUBILITY IN WATER
When liquid PEGs are mixed with water, a volume contraction takes place. 
When equal parts by weight PEG 400 and water are mixed together, this contraction amounts to about 2.5%.

At the same time a marked heat effect occurs.
The temperature rise taking place when equal parts by weight PEG and water are mixed is about 12°C for PEG 200 and about 14°C for PEG 600.
Even solid PEG grades have excellent solubility in water. 
For example, 75 parts by weight of PEG 1000 can be dissolved at room temperature in only 25 parts by weight water.
Although the solubility in water falls slightly with increasing molar mass, it does not fall below 50% even in the case of PEG 35000. 
The dissolving process can be greatly accelerated by heating about the melting point.
PEGs exhibit nonionic behaviour in aqueous solution. 
They are not sensitive to electrolytes and are therefore also compatible with hard water.

NON-VOLATILITY AND THERMAL STABILITY
PEGs are non-volatile, a factor of consider able importance in connection with their use as plasticizers and humectants.
If a certain weight loss is established despite the non-volatility of PEGs when maintained at a constant temperature of 150°C and above (e.g. when used as heating bath liquids), this is due not to evaporation but to loss of volatile products of decomposition.
The breakdown products of PEGs may vary, depending on the ingress of air; apart from water, carbon dioxide and aldehydes, simple alcohols, acids and glycol esters are formed.
Troublesome fumes from decomposition products have not been known to have an adverse effect on health.

Since the lower PEG grades are hygroscopic, moisture may be reabsorbed in the case of fairly long down times.
At temperatures above 100°C it is essential to add a suitable antioxidant to PEG. 
The type an quality of antioxidant is governed by the requirements imposed on PEG. 
Thus, not only the temperature and dwell time but also the physiological properties of the antioxidant and its solubility or insolubility in water must be taken into consideration. 
Where exposure to high thermal stress is involved, up to 3% antioxidant should be added. 

The following substances have proved effective as antioxidants:
1. trimethyl dihydroquinoline polymer
2. diphenylamine derivatives
3. phenothiazine
4. phenyl-alpha-naphtylamine
5. 4,4‘-methylene-bis.2,6-di-tert.-butylphenol
6. butylated hydroxyanisole (BHA)
7. methoxy phenole (hydroxyanisole)
As the following fi gure shows, oxidative decomposition can be slowed down considerably by the addition of antioxidants even at high temperatures (200°C). 
The bath was stabilized with 3% of one of the inhibitors numbered 1 to 4 in turn. 
No major differences were observed between the individual substances.
The pure thermal egradation without presence of oxygen can hardly be infl uenced with antioxidants.
Curve 1 applies to the following stabilizers (3% addition):
- trimethyl dihydroquinoline polymer
- diphenylamine-styrene adduct
- phenothiazine
- phenyl-alpha-naphtylamine
The phenolic stabilizers numbered 5-7 in the list are effective only at lower temperatures
– up to about 150°C - but have two advantages:they cause less discoloration and some of them are water-soluble.
The ingress of air should be excluded if possible or the bath should be blanketed with an inert gas atmos phere (nitrogen, carbon dioxide, etc.). 
This applies particularly to temperatures between 200 and about 220°C.
Hot PEGs attack iron and steel only slightly, but as a precaution when liquid PEGs are used, a certain margin of alkalinity should be created by the addition of about 0.3% hydrated borax or triethanolamine. 
Other materials should be tested to establish their resistance to corrosion by PEGs.


HYGROSCOPICITY
The liquid PEG grades are hygroscopic,although not to the same extent as diethylene glycol or glycerol for example. 
The ability to absorb water decreases with increasing molar mass.
A rule of thumb is: With a relative humidity of about 50% PEG 200 has about ¾ of the hygroscopicity of glycerol. 
PEG 400 has about half, PEG 600 a third and PEG 1000 only a quarter.
PEG 2000 and higher grades are no longer hygroscopic.
PEGs take moisture from the air until an equilibrium is reached. 
By plotting the water content of the substance in the equilibrium state as a function of the relative humidity, absorption isotherm is obtained.
The moisture absorption of lower glycols such as monoethylene glycol, diethylene glycol or 1,2-ropylene glycol corresponds roughly to that of glycerol.
An adaptable moderate hygroscopicity may be advantageous for a conditioning agent because products treated with it are less sensitive to climatic changes and have better storage stability.


SOLUBILITY PROPERTIES
The excellent solubility characteristics of PEGs are of great importance in relation to their applications. 
Two advantages are especially significant:
Firstly, the ability of PEGs to dissolve many substances and, secondly, their good solubility in numerous solvents.
In the preparation of aqueous solutions PEGs sometimes act as specifi c solubilizers.
The dissolving power and the solubility of PEGs decrease as the molar mass increases.
Both properties are improved by heating. 
Here is a list of solvents in which the liquid PEGs are very readily miscible and in which the solid
PEGs dissolve:

Alcohols 
e.g. ethanol, 
isopropanol,
benzyl alcohol

Esters 
e.g. 
methyl acetate,
butyl acetate

Glycol ethers 
e.g.
methyl glycol,
butyl glycol and their acetates

Ketones 
e.g. acetone, 
cyclohexanone

Chlorinated 
e.g. ethylene chloride,
hydrocarbons 
chloroform

Benzene 
e.g. benzene, xylene hydrocarbons

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