Tao Hong-Wen,Wang Xia,Yi Ping-Gui,Deng Zhi-Hong,Yu Xian-Yong,Li Xiao-Fang
A class of stereo-isomerically-pure alkanediol monoglycosides, 2-hydroxyethyl per- O -acetyl pyranosides ( IIIa-IIIf ), was conveniently prepared by a one-pot reaction of per- O -acetylated pyranoses ( Ia-If ) and 2-( tert -butyldimethylsilyloxy)ethanol ( II ) with catalysis by BF 3 ·OEt 2 . The α -( IIIa ) or β -linked glycosides ( IIIb-IIIf ) with 1,2- trans -configuration were obtained from glycosyl donors with participation of the neighbouring 2- O -acetyl group. BF 3 ·OEt 2 , along with hydrogen fluoride released from BF 3 ·OEt 2 under the experimental conditions used, facilitates the subsequent de-protection of siloxane to successfully afford 2-hydroxyethyl per- O -acetyl-pyranosides.
Halohydrin esters could be versatile synthetic reagents, but their conventional synthesis commonly involved hazardous ethylene oxide. An economic, mild, safe and scalable one-step halohydrin esters synthesis was achieved from easily accessible NaX, concentrated sulfuric acid, and polyol esters. The halohydrin esters products were applied in hydroxyethylation reactions with various nucleophiles in replacement of EO. Repetition of the protocol allowed unsymmetric difunctionalization of diol esters. The mechanism likely involves acyloxonium intermediate through neighboring group participation.
The development of thermosetting polyurethane elastomers (TPUEs) face an inherent contradiction between mechanical robustness and re-processability in covalent adaptable networks (CANs), where conventional dynamic bonds either compromise strength (<20 MPa) or require prohibitively high activation temperatures (>150 °C). Herein, we address this long-standing challenge through an innovative dynamic crosslinking strategy based on neighboring-group participation (NGP) of thiabicyclo [3.3.1] nonane (S-BCN), constructing ionic CAN (SPU 2MC ). The double chair-conformation and cation-π interactions in SPU 2MC synergistically enhance mechanical strength (31.1 MPa tensile strength, a 215% increase compared to the glycerol-crosslinked control group (GPU) at the same crosslinking density). Simultaneously, rapid dynamic bond exchange enabled by the NGP allows reprocessing at 110 °C (thermal recycling) and 60 °C (solvent recycling). Benefiting from the high charge density, SPU 2MC also exhibits intrinsic antimicrobial activity (>99.9% inhibition against E. coli and S. aureus ) by adhering to bacterial cell walls and disrupting membrane integrity. For the first time, a catalyst-free dynamic crosslinking strategy achieves synergistic optimization of mechanical performance, re-processability, and antibacterial functionality within a single TPUE system. Such materials show great promise for emerging applications in flexible electronics and protective components.
Covalent adaptable networks (CANs) represent a transition material combining favorable features of thermosets and thermoplastics. However, it is still a huge challenge to simultaneously achieve fast reprocessability and high performance for CANs. Here, we designed catechol-based acetal CANs to achieve continuous reprocessing without sacrificing thermal and mechanical properties. A small-molecule model study demonstrated the significantly accelerated acetal exchange by neighboring group participation (NGP) of phenolic hydroxyl. Using this internally catalyzed acetal chemistry, a series of CANs with a broad range of properties were simply prepared from bio-based epigallocatechin gallate (EGCG) and tri(ethylene glycol) divinyl ether (TEGVE) via one-step “click” cross-linking without using catalysts or releasing small-molecule byproducts. The dynamic nature of the CANs was confirmed via stress relaxation and multiple recycling methods including extrusion. While the dense cross-link density and high rigidity of the network provided high solvent resistance and mechanical properties. This work provides a promising and practical method to produce fast-reprocessing dynamic covalent polymer networks with dense cross-link density and superior performance.
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