Controllable Synthesis of Heterofunctionalized Polyethers via Intramolecular Phosphonium Bisborane Lewis Pair-Catalyzed Immortal Ring-Opening Polymerization
Xiaowu Wang, Minmin Shi, Jiwen Hui, Xinhui Kou, Wang Jiansen, Rong‐Lin Zhong, Zhibo Li
Abstract
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.