*2.3.1 Glycerol oligomers and polymers*

The main route for preparing di-, tri-, tetra- and polyglycerol is by direct oligomerization or polymerization of glycerol using acid or base catalysts, such as potassium carbonate or sulfuric acid. The base catalyst is usually more efficient due to its better solubility in glycerol, albeit with poor selectivity [44]. Glycerol oligomers and polymers have hydrophilic heads which makes them useful for surfactant applications. By careful control of their length and branching during syntheses, desirable physiochemical properties can be built into them such that they can be used as lubricants, polymers and solvents. They have also been earmarked as replacement solvents for fossil-derived glycol ethers in paints, inks and cleaning agents [45].
