Exploration of the Synergistic Effect in a One-Component Lewis Pair System: Serving as a Dual Initiator and Catalyst in the Ring-Opening Polymerization of Epoxides

Ring-opening polymerization (ROP) is a powerful approach to prepare well-defined polymers. Herein, a one-component Lewis pair strategy was adopted, and two delicate Lewis pairs 1–2 were rationally designed and conveniently synthesized. Lewis pairs 1–2 featured an electropositive phosphonium cation, two electrophilic boron centers involving two 9-borabicyclo[3.3.1]nonane moieties, and a nucleophilic halide (Br– or I–). Lewis pair 1–2-mediated ROP of propylene oxide (PO) exhibited activity (turnover frequency = 3600 h–1) with a living characteristic and low catalyst feeding (0.003 mol %) and afforded an extremely high-molecular-weight α-halide/ω-OH polypropylene oxide (PPO, Mn = 489.5 kg/mol) under mild conditions (−30 to 0 °C). We highlight the success of the one-component Lewis pair strategy to achieve living PO polymerization and extremely high-molecular-weight PPO attributing to two important factors: better control (less transfer reaction) and rapid polymerization kinetics, which takes full advantage of the unique structures and the synergistic effect of 1–2. A preliminary investigation demonstrated that water can be added to the polymerization setup and served as a chain transfer reagent, leading to a controlled polymerization and producing α-hydroxy/ω-OH PPO. The present study provides an insightful mechanistic understanding of the designed one-component Lewis pair systems in epoxide homopolymerization based on spectroscopic data analysis and density functional theory calculations.