A Review on Surfactant (Poly)glyceryl Ether Preparation and Their Application

Alkyl ethers of (poly)glycerol are conceptually interesting as surfactants in that they may obtain both their hydrophobe and hydrophile from renewable resources: fats & oils. Due to the proliferation of biodiesel, glycerin has become abundant and inexpensive (notwithstanding the potential need for purification). This may provide an impetus for its use to produce polyglycerol and (poly)glyceryl surfactants. Polyglyceryl esters fulfil the feature as completely renewable surfactants, and have enjoyed use for a long time, particularly as emulsifiers. However, esters are not stable in high or low pH aqueous media. Ethers may circumvent the issue of stability and make their use attractive under these conditions. A modicum of (poly)glyceryl ether surfactants have been studied both fundamentally and in applications, while a few appear to be commercially available.

Complications are many in consideration of their production of monoalkyl glyceryl ethers (MAGE) or monoalkyl polyglyceryl ethers (MAPGE). Several approaches taken to make them demonstrate issues that emerge. One complexity arises from the trifunctional nature of glycerol. Polyglycerols, which can be used as starting materials are molecularly heterogenous in nature, both because of their oligomeric and isomeric nature. Selectivity to produce (poly)glyceryl ethers from glycerol, glycerol precursors, or polyglycerol is a factor that must be taken into consideration when devising reaction schema. Another complexity arises due to the tendency of mutual insolubility of (poly)glycerol and hydrophobe precursors. Given the considerations in making (poly)glyceryl ethers, their manufacture suffers in comparison to workhorse nonionics, alcohol ethoxylates. Commercially available alcohol ethoxylates, however, do not have a hydrophile derived from renewable resources at present. The hurdle to renewable ethylene oxide (EO) is more costly to make renewable alcohol ethoxylates compared to the nearly exclusive production of EO from petrochemical ethylene. Here a review of literature is provided that may spark further discussion and study of (poly)glyceryl ethers.