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 a...