Nitrogen-Coordinated Boroxines Enable the Fabrication of Mechanically Robust Supramolecular Thermosets Capable of Healing and Recycling under Mild Conditions

The fabrication of mechanically robust polymeric materials capable of self-healing and recycling remains challenging because the mobility of polymer chains in such polymers is very limited. In this work, mechanically robust supramolecular thermosets capable of healing physical damages and recycling under mild conditions are fabricated by trimerization of bi-(ortho-aminomethyl-phenylboronic acid)- and tri-(ortho-aminomethyl-phenylboronic acid)-terminated poly­(propylene glycol) oligomers (denoted as Bi-PBA-PPG and Tri-PBA-PPG, respectively). The resultant supramolecular thermosets are cross-linked by dynamic covalent bonds of nitrogen-coordinated boroxines. The mechanical properties of the supramolecular thermosets can be systematically tailored by varying the ratios between Tri-PBA-PPG and Bi-PBA-PPG, which changes the cross-linking density of nitrogen-coordinated boroxines and the topology of the supramolecular thermosets. The mechanically strongest supramolecular thermosets with a molar ratio of Tri-PBA-PPG to Bi-PBA-PPG being 1:2 have a glass transition temperature of ∼36 °C, a tensile strength of ∼31.96 MPa, and a Young’s modulus of ∼298.5 MPa. The high reversibility of nitrogen-coordinated boroxines and the flexibility of poly­(propylene glycol) chains enable the supramolecular thermosets with the strongest mechanical strength to be highly efficiently healed at 55 °C and recycled under a pressure of 4 MPa at 60 °C to regain their original mechanical strength and integrity

Nitrogen-Coordinated Boroxines Enable the Fabrication of Mechanically Robust Supramolecular Thermosets Capable of Healing and Recycling under Mild Conditions

The fabrication of mechanically robust polymeric materials capable of self-healing and recycling remains challenging because the mobility of polymer chains in such polymers is very limited. In this work, mechanically robust supramolecular thermosets capable of healing physical damages and recycling under mild conditions are fabricated by trimerization of bi-(ortho-aminomethyl-phenylboronic acid)- and tri-(ortho-aminomethyl-phenylboronic acid)-terminated poly­(propylene glycol) oligomers (denoted as Bi-PBA-PPG and Tri-PBA-PPG, respectively). The resultant supramolecular thermosets are cross-linked by dynamic covalent bonds of nitrogen-coordinated boroxines. The mechanical properties of the supramolecular thermosets can be systematically tailored by varying the ratios between Tri-PBA-PPG and Bi-PBA-PPG, which changes the cross-linking density of nitrogen-coordinated boroxines and the topology of the supramolecular thermosets. The mechanically strongest supramolecular thermosets with a molar ratio of Tri-PBA-PPG to Bi-PBA-PPG being 1:2 have a glass transition temperature of ∼36 °C, a tensile strength of ∼31.96 MPa, and a Young’s modulus of ∼298.5 MPa. The high reversibility of nitrogen-coordinated boroxines and the flexibility of poly­(propylene glycol) chains enable the supramolecular thermosets with the strongest mechanical strength to be highly efficiently healed at 55 °C and recycled under a pressure of 4 MPa at 60 °C to regain their original mechanical strength and integrity

Noncrystalline Hybrid Lead Halides with Liquid-Polymer Characteristics

Hybrid lead halide (HLH) semiconductors, particularly those featuring perovskite and its derivative structures, have been popular materials with many promising optoelectronic applications. In general, HLHs are predominantly crystalline solids, whether they are bulk single crystals, microcrystals, or nanocrystals. This paper shows that when some short-chain Jeffamine, a widely used polyetheramine, is used as the organic species, the resultant HLH would become noncrystalline with unusual liquid-polymer-like characteristics. In this material, Jeffamine ammoniums and lead halide octahedron frameworks are both arranged amorphously, while its optical properties are similar to those of crystalline HLHs. In contrast to conventional organic species, Jeffamine exhibits a disordered molecular packing, which is believed to account for the peculiar characteristics of the HLH products. Through A-site engineering with Jeffamine, even classic lead halide perovskites such as CsPbBr3 can acquire partial noncrystallinity and transform into a liquid-polymer-like form. This discovery demonstrates that Jeffamine as a novel organic species would confer liquid-polymer properties to the products, which may provide a strategy to transform HLH materials and classic halide perovskites into special “liquid semiconductors”, thereby potentially enabling new processing techniques and new designs of soft electronics

Atomic-Level Modulation-Induced Electron Redistribution in Co Coordination Polymers Elucidates the Oxygen Reduction Mechanism

Regulating the atomic arrangement and electron redistribution is beneficial for tuning catalytic oxygen reduction reaction (ORR) performance and deciphering the intrinsic mechanism. Herein, we modulate the charge density around Co centers by designing and synthesizing three Co coordination polymer catalysts, including Co-DABDT (DABDT = 2,5-diaminobenzene-1,4-dithiol, Co–N2S2), Co-BTT (BTT = 1,2,4,5-tetramercaptobenzene, Co–S4), and Co-BTA (BTA = 1,2,4,5-benzenetetramine, Co–N4), to explore the structure–activity relationship between the coordination environment and ORR performance. Because of the high electronegativity of S compared to N atoms, the charge density of Co increases in the order of Co-BTA → Co-DABDT → Co-BTT. Experimentally, Co-DABDT@CNTs with Co–N2S2 delivers a remarkable half-wave potential of 0.85 ± 0.002 V, outperforming Co–N4 and Co–S4 and even Pt/C (0.84 ± 0.003 V). Zinc–air batteries using Co-DABDT@CNTs as the air cathode catalyst also demonstrate excellent power density and stability. The systematic characterization and theoretical simulation reveal that the charge redistribution on Co and S sites of Co–N2S2 would both effectively optimize and stabilize the key intermediate (OOH*) with the assistance of hydrogen bonding interactions between intermediates and active S atoms (*OO–H···S). Interpreting the mechanism of ORR in the coordination sphere provides a feasible way to improve catalytic activity at an atomic level