MPEG, short for methoxypolyethylene glycol, is one of the most versatile water-soluble polymers in the chemical industry. Because it combines hydrophilicity, low toxicity and good biocompatibility, it appears in products ranging from pharmaceutical formulations and cosmetics to paints, coatings and biomedical materials. This article explains what MPEG is, how the different grades differ, and where each grade is most commonly used.
What Is MPEG Polyethylene Glycol?
MPEG is a monomethyl ether of polyethylene glycol. In its structure, one terminal hydroxyl group of the PEG chain is replaced by a methoxy group, giving the general formula CH3O(CH2CH2O)nH. This single structural change reduces the number of reactive end groups and makes the molecule more stable than unmodified PEG in many formulations.
Depending on the molecular weight, MPEG is a colorless to pale yellow liquid, a white paste or a white flake. It is soluble in water and in many organic solvents such as ethers, alcohols and esters, and it has low viscosity and low toxicity. The terminal hydroxyl group remains available for further reactions such as esterification, oxidation and hydrogenation, which is why MPEG is a common intermediate in the synthesis of surfactants and polymer modifiers.
Grades and Key Specifications
MPEG is produced in a range of molecular weights, and the hydroxyl value is the most convenient indicator of molecular weight: the higher the molecular weight, the lower the hydroxyl value. Typical grades and their approximate specifications are shown below.
| Grade | Appearance at 25 C | Hydroxyl value mgKOH/g |
| MPEG-200 | Colorless liquid | 255-312 |
| MPEG-350 | Colorless liquid | 146-178 |
| MPEG-550 | Colorless liquid | 93-113 |
| MPEG-750 | White paste | 68-83 |
| MPEG-1000 | White paste | 51-61 |
| MPEG-2000 | White flake | 25-31 |
| MPEG-2400 | White flake | 21-26 |
In practice, the pH of a 1% aqueous solution is typically 5.0-7.0 and the color (Pt-Co) is usually below 40 for all grades.
Applications in Pharmaceuticals
In pharmaceutical development, MPEG is used mainly to improve the solubility of poorly water-soluble drugs. It is also incorporated into controlled-release formulations, where it helps modulate the release profile of the active ingredient. In biopharmaceuticals, MPEG and its derivatives are used to enhance the stability of proteins and peptides, and PEGylation with methoxy-PEG chains is a standard strategy for extending the circulation time of therapeutic proteins.
Applications in Cosmetics and Personal Care
MPEG acts as an emulsifier and moisture stabilizer in creams, lotions and other personal care products. It helps immiscible ingredients stay uniformly mixed, keeps the product stable over time, and provides a moisturizing effect on the skin. Because it is mild and low in toxicity, it is a common component of skin care and hair care formulations.
Industrial and Biomedical Applications
Outside pharma and cosmetics, MPEG is used to create biodegradable polymers for tissue engineering and drug delivery systems. It also functions as a surfactant in paints, coatings and other industrial products, and as a lubricant or antistatic agent in various manufacturing processes. The methoxy end group makes MPEG-based surfactants less prone to unwanted reactions, which is an advantage in emulsion polymerization and waterborne coatings.
How to Select the Right MPEG Grade
The choice of grade depends on the application. Low-molecular-weight liquid grades are convenient for reactions and liquid formulations, while high-molecular-weight flake grades provide higher viscosity, better film-forming properties and slower release in solid formulations. Buyers should confirm the required hydroxyl value, molecular weight distribution and residual water content with the supplier and request a certificate of analysis for each batch.
Frequently Asked Questions
What does MPEG stand for?
MPEG stands for methoxypolyethylene glycol, also called polyethylene glycol monomethyl ether.
Is MPEG the same as PEG?
No. MPEG is a monomethyl ether derivative of PEG: one terminal hydroxyl group of the PEG chain is replaced by a methoxy group, which changes its reactivity and stability.
Is MPEG soluble in water?
Yes, MPEG is soluble in water and also in many organic solvents including ethers, alcohols and esters.
What is MPEG used for in pharmaceuticals?
It improves the solubility of poorly soluble drugs, supports controlled-release formulations and enhances the stability of proteins and peptides, for example through PEGylation.
What is the difference between MPEG-200 and MPEG-2000?
The number indicates the approximate molecular weight. MPEG-200 is a liquid with a hydroxyl value of about 255-312 mgKOH/g, while MPEG-2000 is a white flake with a hydroxyl value of about 25-31 mgKOH/g.
How should MPEG be stored?
Store in a cool, dry place in tightly sealed containers to avoid moisture uptake and contamination, and keep away from strong oxidizing agents.
