Overview of Various Polyethers – Polyoxyalkylene Pentol

There are two types of pentol polyoxypropylene ether with five hydroxyl groups. One type uses diethylenetriamine (DETA) as an initiator, which polymerizes with propylene oxide to produce a five-hydroxyl nitrogen-containing polyether that exhibits self-catalytic properties. The other type uses xylitol, a compound with five hydroxyl groups, as an initiator and undergoes catalytic polymerization with propylene oxide, forming a five-hydroxyl polyether. Both types of polyethers are suitable for rigid polyurethane foam. Due to the high viscosity of five-hydroxyl polyether, in actual production, initiators with high functionality are typically mixed with low-functionality initiators to prepare polyether polyols with a functionality between 3 and 5.

Polyether Pentol Produced with Diethylenetriamine as an Initiator: This polyether pentol is a transparent, homogeneous, viscous liquid. For example, a polyether pentol with an average molecular weight of 398 and a hydroxyl value of 648 mg KOH/g has a viscosity of approximately 100 Pa·s (at 30°C), a color (APHA) below 200, and a water content below 0.1%. This viscosity is quite high. Due to its structure containing tertiary amines, it can act as a catalytic cross-linking agent for rigid and semi-rigid foams. When blended with low-functionality polyethers such as tri- or tetra-functional polyethers, it produces rigid foams with high dimensional stability and compressive strength, making it especially suitable for on-site spray foaming formulations.

Polyoxypropylene Pentol Derived from Xylitol: The preparation conditions are similar to those of glycerol-based polyoxypropylene. Due to xylitol’s high hygroscopicity, further dehydration under vacuum is necessary before polyether synthesis; otherwise, it would severely impact polyether quality. By using 100 parts of propylene oxide and 40–42 parts of xylitol, with 0.5 parts of potassium hydroxide as a catalyst, polymerization can occur at 100–110°C, producing polyoxypropylene pentol with a hydroxyl value of (500±20) mg KOH/g, an average molecular weight of 550±50, an acid value below 0.15 mg KOH/g, and a water content below 0.1%. This polyether polyol appears as a light-yellow, viscous liquid. Polyoxypropylene pentol based on xylitol is mainly used as a base material for rigid foams, characterized by its excellent high-temperature resistance (up to 150°C) and dimensional stability.

Rigid foams made from polyether pentol exhibit better temperature resistance and dimensional stability compared to rigid foams based on glycerol or pentaerythritol polyethers.