Nonstrained γ-Butyrolactone to High-Molecular-Weight Poly(γ-butyrolactone): Facile Bulk Polymerization Using Economical Ureas/Alkoxides

Abstract

We disclose an efficient catalyst system of commercial ureas/alkoxides for the challenging ring-opening polymerization (ROP) of bioderived “nonpolymerizable” γ-butyrolactone (γ-BL). This effective polymerization can not only be performed under mild conditions like bulk polymerization, higher monomer ratio, and elevated temperature (−20 °C comparing to −40 °C), but also obtains high-molecular-weight poly(γ-butyrolactone) (PγBL) (Mn up to 68.2 kg/mol). To our knowledge, this is a big progress in the research area of ROP of γ-BL, which provides a promising prospect for the industrial-scale methodology of PγBL production. Structural analysis including NMR and MALDI-TOF, along with mechanistic computational studies based on DFT calculations, show that urea anion acts as a bifunctional catalyst, which activates the alcohol initiator and γ-BL before obeying an anionic polymerization. Furthermore, the catalytic activities of ureas/alkoxides systems have been optimized using the ureas with electron-donating groups which are proved to have lower activation barrier by computational calculation.