Controllable Synthesis of Heterofunctionalized Polyethers via Intramolecular Phosphonium Bisborane Lewis Pair-Catalyzed Immortal Ring-Opening Polymerization

A metal-free phosphonium bisborane Lewis pair (PBB-Br) was demonstrated to realize the immortal ring-openingpolymerization(iROP) of propylene oxide (PO) under mild conditions with alcoholsas 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 findingsindicated the iROP feature of PBB-Br-catalyzed PO polymerization.The rapid, reversible, and quantitative chain transfer assured theiROP characteristic for an intramolecular Lewis pair catalyst PBB-Br, so various well-defined heterofunctionalized PPOswere easily produced. All the alpha,omega-difunctionalized PPOswere carefully characterized. Density functional theory (DFT) calculationsreveal that the chain transfer to the CTA process is almost barrierless(0.8 kcal mol(-1)) and thermodynamically favorableas compared to chain propagation. Moreover, PPO-based block copolyetherswere easily obtained in one-pot using epoxide mixtures. This researchdemonstrated that the delicately designed intramolecular synergisticLewis pair offered a powerful and controllable method to prepare variousheterofunctionalized PPO samples with high values.