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, M n = 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.

A metal-free phosphonium bisborane Lewis pair (PBB-Br) was demonstrated to realize the immortal ring-opening polymerization (iROP) of propylene oxide (PO) under mild conditions with alcohols as chain-transfer agents (CTAs). Narrow dispersed poly(propylene oxides) (PPOs) with controllable molecular weights predicted from the [PO]0/([PBB-Br]0 + [CTAs]0) molar ratio were obtained in quantitative conversion. These findings indicated the iROP feature of PBB-Br-catalyzed PO polymerization. The rapid, reversible, and quantitative chain transfer assured the iROP characteristic for an intramolecular Lewis pair catalyst PBB-Br, so various well-defined heterofunctionalized PPOs were easily produced. All the α,ω-difunctionalized PPOs were carefully characterized. Density functional theory (DFT) calculations reveal that the chain transfer to the CTA process is almost barrierless (0.8 kcal mol–1) and thermodynamically favorable as compared to chain propagation. Moreover, PPO-based block copolyethers were easily obtained in one-pot using epoxide mixtures. This research demonstrated that the delicately designed intramolecular synergistic Lewis pair offered a powerful and controllable method to prepare various heterofunctionalized PPO samples with high values.

A metal-free phosphonium bisborane Lewis pair (PBB-Br) was demonstrated to realize the immortal ring-opening polymerization (iROP) of propylene oxide (PO) under mild conditions with alcohols as chain transfer agents (CTAs). Narrow dispersed poly(propylene oxide) (PPO) with controllable molecular weights predicted from [PO]0/([PBB-Br]0+[CTAs]0) molar ratio were obtained in quantitative conversion. These indicated the iROP feature of PBB-Br-catalysed PO polymerization. The rapid, reversible and quantitative chain transfer assured the iROP characterisitc for intramolecular Lewis pair catalyst PBB-Br, so various well-defined heterofunctionalized PPOs were easily produced. All the α,ω-difunctionalized PPOs were carefully characterized. Density functional theory (DFT) calculations reveal the chain transfer to CTA process is almost barrierless (0.8 kcal. mol-1) and thermodynamically favorable as compared to chain propagation. Moreover, PPO-based block copolyethers were easily obtained in one-pot using epoxide mixtures. This research demonstrated that the delicately designed intramolecular synergistic Lewis pair offered a powerful and controllable method to prepare various heterofunctionalized PPO samples with high values.