MPEG - Polyethylene Glycol Monomethyl Ether — Frequently Asked Questions

Because it prevents crosslinking. Ordinary polyethylene glycol carries a hydroxyl at each end, so any reaction can occur at either or both, producing bridged products and a mixture of outcomes. MPEG has one end capped with a methyl group and one reactive hydroxyl, so it attaches at a single defined point. That monofunctionality is what makes controlled PEGylation and surfactant synthesis possible.

PEGylation is attaching PEG chains to a protein or drug molecule to extend its circulation time, reduce immune recognition and improve solubility. It requires a PEG that can bond at one end only, since a bifunctional PEG would crosslink protein molecules together. MPEG provides that, and pharmaceutical grades are specified on polydispersity, residual ethylene oxide and dioxane, and metals.

By average molecular weight, since the material is a distribution rather than a single compound. Grades run from a few hundred to several thousand daltons, with low molecular weight grades being viscous liquids and higher ones waxy solids. Polydispersity, the width of that distribution, is a critical specification for pharmaceutical use.

As the hydrophilic block in non-ionic surfactants and dispersants, in concrete superplasticisers where PEG side chains provide steric repulsion between cement grains, and in cosmetics. In each case the single reactive end allows the PEG chain to be grafted onto a hydrophobe without bridging two of them.