These are aliphatic polyethers obtained by oxidation of an olefin (ethylene or propylene) and then by reaction with an alcohol.
These oils have exceptional lubrication properties, particularly in the presence of high sliding stresses, and high thermal conductivity, which can favour their use in cases of significant temperature differences between the inner and outer rings.
Their polar structures provide a high affinity with metals and a high capacity to resist load and wear. With a high viscosity index, they cover a wide temperature range and form very little residue after exposure between 150°C and 200°C.
Their main disadvantages are the solubility of polyethylene glycol types in water, their incompatibility with other types of oils and their negative actions on the most commonly used elastomers and plastics.