Ring-opening polymerization of <italic>γ</italic>-butyrolactone catalyzed by organic quaternary ammonium base catalysts

In this study, a low-cost quaternary ammonium base, tetrabutylammonium hydroxide (TBAH), was combined with benzyl alcohol (BnOH) through a simple dehydration process to form a catalytic system for the efficient ring-opening polymerization (ROP) of γ-butyrolactone (γ-BL). Under the conditions of −40 °C and a monomer concentration of 10 M, the conversion can reach up to 76% after 4 h, and the number-average molecular weight (Mn) of the obtained poly(γ-butyrolactone) (PγBL) was as high as 11.1 kg/mol. The Mn of PγBL could be effectively controlled by varying the monomer to initiator ratio. Furthermore, this strategy was also applied to synthesize bisfunctional polyester polyols, where TBAH activated various diols via dehydration to efficiently initiate polymerization. In addition, TBA+/BnO‒ system facilitated the copolymerization of γ-BL and ε-caprolactone (ε-CL) at room temperature. A series of random copolyesters (PBL-co-PCL) with tunable γ-BL content were successfully synthesized by adjusting the γ-BL/ε-CL feed ratio. The melting points (Tm) of these copolymers could be tuned in the range of 15.7–35.1 °C by varying the copolymer composition. This catalytic system exhibits prominent advantages such as being metal-free, operationally simple, and low-cost, providing a new and highly promising approach for the large-scale synthesis of γ-BL-based polyesters.