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

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.

A Binary Silicon‐Centered Organoboron Catalyst with Superior Performance to That of Its Bifunctional Analogue

“…Halogen‐free and hydroxy telechelic PPOs with linear and star‐like structures were synthesized. For organoborane‐mediated catalysis, the current intramolecular heteronuclear synergies are mainly limited to the synergies between boron and the groups containing nitrogen, phosphorus, or thioureas, [12i,j,l,37a–e] so this discovery might broaden the scope of research and provide inspiration for the future design of multicore organocatalysts with active catalytic sites possessing different electron densities. Such work is currently underway in our laboratory.…”

“…The rule for bifunctional catalyst design is also suitable for the metal‐free catalyst system [12a–m] . For example, we have reported the construction of organoboron catalysts featuring intramolecular electrophilic boron center(s) and a nucleophilic quaternary ammonium salt, which have shown higher catalytic performance and selectivity than their binary analogues (Figure 1a, 1b).…”

Organoboron-mediated polymerizations

“…Addition of heterofunctionalized chain-transfer agents led to the formation of functional PPO samples with controllable molecular weights. 241…”

Metal-Free Synthesis of Biodegradable CO2-Based Oligo(carbonate-ester) Diols as Building Blocks for Thermoplastic Polyurethanes

“…Though the molar mass of diols can be easily tuned by changing the feeding ratio of PO/initiator, high loadings of TEB and initiators (PO/initiator/TEB = 10/1/2.8 to obtain diols with molar mass of 1100 Da) are economically unfavorable for industrialization. Recently, various bidunctional boron-based organocatalysts have been reported and showed high catalytic productivity and efficiency for epoxides/CO 2 copolymerization owing to the synergestic effect from the Lewis acid and base in the one molecule. , It is worth noting that those bifunctional catalysts exhibit excellent proton tolerance, therefore, enabling outstanding productivity for polycarbonate diols with high oligomer selectivity even at low catalyst loadings. − Our recent study explored the commercial TEB/bis­(triphenylphosphine)­iminium chloride (PPNCl) system to synthesize PPCDL with well-controlled molar mass, narrow PDI, and expected chain-end functionality . However, expensive PPNCl leads to high cost, which is not conducive to large-scale production.…”