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Traditional epoxy resins are of technological significance for structural adhesives and composite materials, as well as many others. However, brittleness limits its further development, and achieving a combination of toughness and rigidity in epoxy networks remains a great challenge. In this work, we designed and synthesized low-temperature curable, tough and repairable epoxy networks via hindered urea bond (HUB) crosslinking strategies. Mechanical testing revealed that the material exhibited simultaneously improved toughness and stiffness, and specifically, tensile strength, elongation at break, and toughness were able to reach 78.2 MPa, 8.61%, and 4.63 MJ · m−3, respectively. More importantly, the dynamic exchange of HUB dispersed between polymer chains enables HUB crosslinked epoxy with thermal-triggered reparability and recyclability. In addition, thermal properties, chemical stability and water resistance of toughened epoxy samples were also characterized. This work provides a practical guidance for the exploration of high-performance epoxy with the potential to be extended to other polymers. [ABSTRACT FROM AUTHOR]

Intrinsic self-healing waterborne polyurethane (WPU) is an environmentally friendly, economically viable, and practical novel intelligent material. However, the key to achieving practical applications lies in the remote activation of repair in self-healing materials and the excellent mechanical properties of the matrix. In this study, we introduce quadruple hydrogen bonding in the polyurethane backbone. We have incorporated a novel two-dimensional sheet-like material, MXene, to achieve visible light remote-driven self-healing of material hydrogen bonds while enhancing the material’s mechanical properties. By utilizing the MXene supernatant, this approach not only resolves the issues of poor stability and easy sedimentation of MXene nanosheets in water-based polymers but also helps to prevent resource wastage. Our research results demonstrate that the composite film exhibits a tensile strength of 6.55 MPa and a fracture elongation of 604%. Additionally, quadruple hydrogen bonds in the WPU chains enable rapid self-healing of microcracks under visible light irradiation at 300 mW/cm2, with complete disappearance within 80 min. [ABSTRACT FROM AUTHOR]

Objective: In this study, we evaluated whether exercise prior to memory encoding or during memory consolidation can influence episodic memory function after being exposed to a stressful environment. Methods: We conducted 3 between-group randomized controlled experiments among young adults. We assessed episodic memory (via logic memory task) at the beginning of the experiment and approximately 45 minutes later. Across the 3 experiments, we varied the temporal period (eg, before memory encoding or during consolidation) of the acute bout of exercise (15-minute moderate-intensity exercise) and psychological stress induction. Results: Across all 3 experiments there was a statistically significant main effect for time for memory function, but there were no time x group interaction effects. Conclusion: Memory declined across the 2 assessment periods, but for all 3 experiments, exercise was not associated with memory function after being exposed to a stressful stimulus.

Modulating controlled radical polymerization is an interesting and important issue. Herein, modulating RAFT polymerization employing photosensitive azobenzenes is achieved. In the presence of azobenzenes and with visible light off, RAFT polymerization runs smoothly and follows a pseudo-first-order kinetics. In contrast, with light on, RAFT polymerization is greatly decelerated or quenched depending on the type and concentration of azobenzenes. Switchable RAFT polymerization of different (meth)acrylate monomers alternatively with light off and on is demonstrated. A mechanism of photoregulating RAFT polymerization involving radical quenching by azobenzenes is proposed., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)