Special Polyether Polyol—Polytetrahydrofuran Polyol

Compared to commonly used polyether polyols such as polypropylene glycol (PPG) and polypropylene oxide-ethylene oxide copolymer polyols in polyurethane foams, polytetrahydrofuran diol (also known as polytetramethylene ether glycol or tetrahydrofuran polyether, abbreviated as PTMEG) is a specialized polyether polyol. While PTMEG was utilized in the early research on polyurethane foams, it is now occasionally used in specialty microcellular foams.

PTMEG is a linear polyether diol terminated with primary hydroxyl groups, with the chemical structure H[O(CH₂)₄]_nOH. It is synthesized through the cationic ring-opening polymerization of tetrahydrofuran (THF). PTMEG is an essential raw material for producing high-performance block polyether-type polyurethane elastomers. Products made with PTMEG exhibit excellent properties such as wear resistance, high strength, good flexibility, aging resistance, hydrolysis resistance, and superior elasticity.

Currently, the industrial production of PTMEG employs both homogeneous and heterogeneous catalytic systems. Homogeneous catalytic systems include methods such as acetic anhydride-perchloric acid, fluorosulfonic acid, and fuming sulfuric acid. However, these methods have significant drawbacks, such as equipment corrosion and severe environmental pollution caused by waste byproducts.  

Since the mid-1980s, research has focused on heteropoly acids (HPA) and their salts as catalysts for THF polymerization. The use of HPA anions as polymerization catalysts for THF has yielded excellent results. This catalyst overcomes the shortcomings of homogeneous catalysts, offering advantages such as reusability, low corrosiveness, no need for neutralization, and minimal environmental pollution. At the same time, it retains the high catalytic efficiency and narrow molecular weight distribution of homogeneous catalysts.

Due to its regular structure and ease of crystallization, PTMEG is generally a waxy solid at room temperature. Common PTMEG products have molecular weights of 1,000 and 2,000, with melting points of 18–22°C and 22–25°C, respectively.