Overview of Various Polyethers — Polyether Diols

The most common polyether diols include polypropyleneglycol (PPG), polytetrahydrofuran diol, polyethylene glycol, and copolymer diols of propylene oxide, ethylene oxide, tetrahydrofuran, and halogenated epoxides.

Compounds containing two active hydrogen atoms, such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and 1,4-butanediol, can serve as initiators for the polymerization of polyether diols.

The polyether diol most commonly used in polyurethane foam is polypropyleneglycol (PPG), formerly known as polypropylene glycol. In practical production, 1,2-propanediol is typically used as the initiator for polypropyleneglycol. As mentioned earlier, the molecular weight of the polyether is determined by the feed ratio of propylene oxide to propylene glycol; as the molar ratio of propylene glycol to propylene oxide increases, the molecular weight of the synthesized polyether decreases while the hydroxyl value increases. For PPG with a molecular weight of 2000, the molar ratio of the initiator (propylene glycol) to the monomer (propylene oxide) is approximately 1.2% to 1.3%.

Polyether diols are primarily used to prepare polyurethane soft foams, elastomers, adhesives, fibers, synthetic leather, and more. The reaction between dihydroxy polyethers and diisocyanates generates linear, straight-chain polyurethanes, thereby increasing foam softness and enhancing elongation properties. The higher the molecular weight of the polyether, the greater the softness and elongation of the final product. Medium molecular weight (e.g., 2000) polyether diols are mainly used as auxiliary polyethers and can be combined with triols to produce polyurethane soft foams.

Traditional Manufacturing Method

The traditional method involves adding a mixture of the initiator (1,2-propanediol or dipropylene glycol) and the catalyst (potassium hydroxide) into a reaction vessel and heating it to 80-100°C. Under vacuum, the moisture in the catalyst is removed to promote the formation of alkoxide. The catalyst is then transferred to the polymerization reactor, where the temperature is raised to 90-120°C. At this temperature, propylene oxide is introduced into the polymerization vessel, maintaining the pressure between 0.07-0.35 MPa. Under these conditions, propylene oxide undergoes continuous polymerization until a certain molecular weight is reached. After evaporating the residual propylene oxide, the polyether mixture is transferred to a neutralization tank, where it is neutralized with an acidic substance, followed by filtration and purification, and finally stabilized to yield the final product.