Highly efficient ring‐opening polymerization of tetrahydrofuran by anhydrous ferric chloride

Abstract

ABSTRACTPoly(tetramethylene ether glycol) (PTMG), widely used as a precursor in the fabrication of commodity polymers, is typically produced byacid‐catalyzed polymerization of tetrahydrofuran (THF). Herein, we report a detailed investigation of the cationic ring‐opening polymerization of THF catalyzed by ferric chloride (FeCl3), which can be considered as a strong Lewisacid. The polymerization reactions were performed in the presence of acetic anhydride at 20°C with FeCl3, which readily produced poly(tetramethylene ether glycol diester) (PTMG_DE). A maximum yield of 79.2% was obtained within 30 min using a FeCl3 to acetic anhydride molar ratio of 5:4. The resulting polymers generally exhibited low molecular weights and a narrow polydispersity index and could be easily converted into PTMG using aqueous NaOH. In contrast with the FeCl3‐acetic anhydride system, other iron‐based catalysts such as FeCl2 and FeCl3·6H2O did not show any noticeable activity in the polymerization of THF. The proposed mechanism involves initiation of the acetyl cation generated by FeCl3, propagation by nucleophilic addition of THF, and termination by the acetate anion, accounting for the high activity of the FeCl3 catalyst for THF polymerization. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47999.