Typically, the formulation of rigid foam polyether polyols will select materials with high functionality and high hydroxyl value to ensure sufficient crosslinking and stiffness. The hydroxyl value of this polyether polyol is usually between 350 and 650 mgKOH/g, and the average functionality is above 3. Rigid foam formulas usually mix two polyethers with an average hydroxyl value of about 400 mgKOH/g.
The functionality of polyether polyols with glycerol as the initiator is relatively low, so the formation rate of the crosslinking network is slow, which makes the rigid foam material have good fluidity. Polyether polyols with amines as initiators have self-catalytic effects and high reaction activity, which can reduce the amount of amine catalysts. Polyether polyols using aromatic diamines as initiators can quickly cure and produce high-strength foams, while also having low thermal conductivity. The price of the initiator has a great influence on the production cost of polyether polyols. Therefore, the initiator of general rigid foam polyether polyols is mainly sucrose and its mixture. In the semi-rigid foam formulation, some high molecular weight soft foam polyethers are usually used, especially highly active polyether polyols and some high-functional low molecular weight rigid foam polyethers.