MPG - Mono Propylene Glycol — Frequently Asked Questions

USP and EP grades are tested to the United States or European Pharmacopoeia monograph, with limits on water, residue on ignition, heavy metals and ethylene and diethylene glycol, and come with documents for pharmaceutical and cosmetic use. Industrial grade is made for resins, antifreeze and de-icing, and is not tested to a monograph. Use the pharmacopoeia grade for any product applied to or consumed by people.

MPG has much lower toxicity than MEG, so it is chosen for heating and cooling systems where a leak could reach food, drinking water, pets or livestock. It gives slightly less freeze protection and higher viscosity at the same concentration, so a stronger mix or larger pumps may be needed. Like MEG, it needs corrosion inhibitors in a finished coolant.

Ethylene glycol and diethylene glycol are toxic, and contamination of pharmaceutical-grade glycols with them has caused serious poisoning incidents. Pharmacopoeia monographs therefore limit each to 0.10% and require testing of every batch. For cosmetic and pharmaceutical use, ask for a certificate of analysis showing both results, and check that the grade and documentation match your application.

MPG is one of the main diols reacted with maleic and phthalic anhydrides to make unsaturated polyester resins. Its methyl side group reduces crystallinity, which gives good compatibility with styrene and a clear, stable resin solution. Resin makers use it alone or with other glycols, such as DPG, to adjust flexibility, toughness and water resistance in marine, tank and casting resins.

MPG is not classified as hazardous under CLP and is not regulated for transport. It has low toxicity and is widely used in personal care and pharmaceutical products. It can still cause mild eye irritation, and it is combustible when heated above its flash point of about 99 °C. Follow the safety data sheet for handling, storage and first aid.