The relationship between different molecular weights of polyethylene glycol (PEG)

The molecular weight of polyethylene glycol is closely related to its physicochemical properties, application characteristics, and biocompatibility. Mainly reflected in the following aspects:

1. Physical state:

Liquid and solid: As the molecular weight increases, the physical state of polyethylene glycol changes. Low molecular weight PEG (usually<600 Da) is typically a colorless, odorless liquid with good fluidity. As the molecular weight further increases, PEG gradually transforms into a semi-solid (about 700-900 Da), until it becomes a high molecular weight solid (>1000 Da), appearing in a waxy or flocculent form.

Melting point and softening point: As the molecular weight increases, the melting point and softening point of PEG rise, which means that high molecular weight PEG requires higher temperatures to melt or soften.

2. Solubility and compatibility:

Water solubility: Low molecular weight PEG has excellent solubility in water, but as the molecular weight increases, its water solubility gradually decreases. Although high molecular weight PEG can still dissolve in water, its dissolution rate and solubility may decrease.

Organic solvents: Low molecular weight PEG has good solubility in many organic solvents such as alcohols, ketones, esters, etc., while high molecular weight PEG may only partially dissolve or be insoluble in certain organic solvents.

Drugs and other active ingredients: Low molecular weight PEG is often used as a solvent or carrier, which can dissolve or disperse a certain proportion of drugs or active ingredients. High molecular weight PEG is more suitable as a matrix or excipient to enhance the solubility and bioavailability of poorly soluble drugs by forming solid dispersions, particles, or nanoparticles.

3. Surface activity and interfacial properties:

Wettability and spreadability: low molecular weight PEG has good wettability and spreadability due to its small molecular weight and strong hydrophilicity, and is suitable for preparing lotion, dispersion or as a wetting agent. These properties of high molecular weight PEG are relatively weak.

Emulsification and dispersion ability: Low molecular weight PEG is more effective as an emulsifier and dispersant than high molecular weight PEG, which may need to be used in combination with other surfactants.

4. Biomedical applications:

Drug delivery system: High molecular weight PEG is commonly used to construct long-acting drug formulations by coupling with drug molecules to form PEGylated drugs, prolonging the circulation time of drugs in the body and reducing immunogenicity. Low molecular weight PEG is less commonly used in such applications.

Biomaterials and medical devices: High molecular weight PEG can be used to prepare hydrogels, coatings or scaffold materials with good biocompatibility, while low molecular weight PEG may be more used as solvent or flushing fluid.

5. Toxicity and Biosafety:

Systemic toxicity: PEG is considered a low toxicity or non-toxic material. Low molecular weight PEG usually has better biodegradability and excretion, while high molecular weight PEG may have a longer retention time in the body, but usually does not cause significant toxic reactions.

Local irritation and allergic reactions: Some reports suggest that high molecular weight PEG, especially when applied topically (such as on the skin or eyes), may cause mild irritation or allergic reactions. Low molecular weight PEG may have lower irritability.