Xinhui Kou

Borane Lewis pair-mediated ROP of epoxides at 25 °C affords α-acyl azide/ω-hydroxyl heterotelechelic polyethers, which undergo Curtius rearrangement and self-polyaddition to yield latent-isocyanate-derived polyurethanes.

Stereoselective polymerization of epoxides has traditionally relied on metal-based catalysts, yet the presence of residual metals restricts their use in sensitive applications such as biomedicine. Chiral borane catalysis offers a promising metal-free alternative, though most reported systems display limited structural diversity and modest stereocontrol. Herein, we report the design and synthesis of enantiopure SPINOL-derived dinuclear borane catalysts that enable highly efficient and stereoselective polymerization of racemic propylene oxide (PO). Under optimized conditions (–20 °C in THF), the catalysts produced isotactic poly(propylene oxide) (PPO) with a meso dyad content ([m]) of 93%. Kinetic studies reveal a distinct enantiomeric matching between catalyst configuration and PO enantiomers, in sharp contrast to the mismatched preference observed with BINOL-based analogues. The polymerization proceeded via an enantiomorphic site-control mechanism, with a maximum selectivity factor (s) of 34.8. These results highlight the potential of SPINOL frameworks as versatile chiral platforms for advancing the development of high-performance borane catalysts in stereoselective polymerization.

Chemoselective polymerization from a mixture of l-LA, CHO and CO₂ enables the synthesis of PLLA, PCHC or PCHC-b-PLLA achieved by PBB-Br. The chemoselectivity depends on the nature of the growing polymer chain end.

Stereoselective ring-opening polymerization of rac -lactide was catalyzed by the proton sponge bisphosphazene HMPN, affording semicrystalline isotactic polylactide with P _m up to 0.93.

Chemoselective terpolymerization can produce polymer materials with diverse compositions and sequential structures, and thus have attracted considerable attention in the field of polymer synthesis. However, the intrinsic complexity of three‐component system also brings great chanllenge, in regard to the reactivity and selectivity of different monomers. Herein, we report the terpolymerization of CO₂/epoxide/anhydride by a binary organocatalytic C₃N₃‐Py‐P₃/TEB (triethylborane) system. Both the activity and chemoselectivity were highly dependent upon the molar ratio of C₃N₃‐Py‐P₃ to TEB, and sequence‐controlled poly(ester‐carbonate) copolymers were readily synthesized through one‐pot/one‐step methodology by tuning the stoichiometric ratio of phosphazene/TEB. In particular, C₃N₃‐Py‐P₃/TEB with a molar ratio of 1/0.5 exhibited an unprecedentedly high chemoselectivity for ring‐opening alternating copolymerization (ROAC) of cyclohexene oxide (CHO) and phthalic anhydride (PA) first and then ROAC of CO₂/CHO. Thus, well‐defined triblock polycarbonate‐b‐polyester‐b‐polycarbonate copolymers can be produced from the mixture of CO₂, CHO and PA using a bifunctional initiator. With C₃N₃‐Py‐P₃/TEB=1/1, tapered copolymers were obtained, while random copolymers with high content of polycarbonate (PC) were synthesized with further increasing the amount of TEB. The mechanism of the unexpected chemoselectivity was further investigated by DFT calculations.

An intramolecular phosphonium borane Lewis pair (PBB-Br) was used for the copolymerization of o-phthalaldehyde (OPA) with epoxides under mild conditions. In particular, poly(OPA-alt-PO) having high molecular weight (Mn = 42.5 kg/mol) with Đ = 1.12 was generated at 25 ℃ using PBB-Br as a highly efficient catalyst. The purity of OPA, temperature and monomer/comonomer feeding ratio effects on the copolymerization were investigated. Subsequently, the degradability and thermal stability of generated polyacetals were studied. Using alcohol as chain transfer agent, random or block polyacetal-polyethers with different structures can be obtained in one-pot synthesis.

Functional P(MVL- co -CL) copolyesters with modifiable pendent double bonds were obtained by chemoselective and controlled ring-opening copolymerization of biorenewable MVL with CL using an organophosphazene/urea binary catalyst.

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.

MALDI-TOF-MS plays important roles in the characterization of various synthetic polymers, which can provide the molecular weight, repeat unit, end groups, polymerization mechanism and other information on the analyte polymers.