Polyether polyol is prepared by ring-opening polymerization of epoxide monomers (such as ethylene oxide, propylene oxide and 1,2-epoxybutane) and a compound containing two or more active hydrogen atoms (called an initiator). In the presence of alkali catalyst, active hydrogen compounds initiate ring opening and oxide addition will continue until the required molecular weight is obtained. The number of hydroxyl groups in polyether polyol is determined by the number of unstable hydrogen atoms in the initiator. If the initiator has two active hydrogen, glycol will be formed. The reactivity of polyether polyol
to isocyanates depends on the initiator and the type of epoxy monomer that ends the ring-opening polymerization. The primary hydroxyl produced by polyol capped with ethylene oxide is more reactive than the secondary hydroxyl produced by propylene oxide, which is ideal for applications requiring rapid curing time. However, the use of initiator based on ethylene oxide and amine can also make the coating more hydrophilic and damage the barrier performance of the coating (such as waterproof membrane), so a good balance between reactivity and hydrophobicity is necessary.
The VOC limitation faced by epoxy coatings increases the use of epoxidized diols and Polyol (also known as reactive diluents) to reduce the use of solvents in epoxy formulations. However, due to the low reactivity or the epoxy ring near the aliphatic chain, the curing time of epoxy coating containing a large amount of reactive diluents can be greatly prolonged. Moreover, reactive diluents increase the cost of epoxy coating formulation. Therefore, due to their low viscosity and high reactivity, polyether polyol makes polyurethane coatings become the substitute of 100% solid epoxy system used in the application of anticorrosive coatings.