A triol‐functional crosslinker combining the thermoreversible properties of Diels–Alder (DA) adducts in one molecule is designed, synthesized, and used as an ideal substitute of a traditional crosslinker to prepare thermal recyclable cross‐linked polyurethanes with excellent mechanical properties and recyclability in a very simple and efficient way. The recycle property of these materials achieved by the DA/retro‐DA reaction at a suitable temperature is verified by differential scanning calorimetry and in situ variable temperature solid‐state NMR experiments during the cyclic heating and cooling processes. The thermal recyclability and remending ability of the bulk polyurethanes is demonstrated by three polymer processing methods, including hot‐press molding, injection molding, and solution casting. It is notable that all the recycled cross‐linked polymers display nearly invariable elongation/stress at break compared to the as‐synthesized samples. Further end‐group functionalization of this single molecular DA crosslinker provides the potential in preparing a wide range of recyclable cross‐linked polymers.
In this work, we report the synthesis and characterization of mesoporous ceria with hierarchical nanoarchitectures controlled by amino acids. During the synthesis procedure, cerium oxalate precipitate was treated hydrothermally with different amino acids as crystallization modifiers, and hierarchically structured cerium oxalate precursors were obtained. Ceria can be produced after thermal decomposition of the cerium oxalate precursors. Structure and properties of the product were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, N2 adsorption analysis, and X-ray photoelectron spectroscopy (XPS) methods. The results indicate that the mesoporous ceria with hierarchical nanoarchitectures are composed of nanosized ceria crystallites as building units and possess high surface area and high concentration of oxygen vacancy. Depending on different amino acids as the crystallization modifiers, the ceria exhibit different morphologies, such as dendritic aggregation of rods, dumbbells of nanorod arrays, or aggregated spheres. It is proposed that both the type of functional side groups and the length of the side groups of the amino acids influence the morphologies of the ceria. Meanwhile, the solvent and hydrothermal treatment temperatures also play important roles in the morphological control. The method reported in this work would be regarded as a general way to fabricate mesoporous metal oxides with hierarchical nanoarchitectures. 相似文献
To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NOx with an ammonia reductant, we employed scanning transmission X-ray microscopy (STXM) to study Cu-exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000-mile aging. X-ray absorption near-edge structure (XANES) measurements were performed at the Al K- and Cu L-edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi-factor-induced catalytic deactivation. In Cu-exchanged MFI, a transformation of CuII to CuI and CuxOy was observed. We also found a spatial correlation between extra-framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of CuI and tri-coordinated Al. By inspecting both Al and Cu in fresh and aged Cu-exchanged zeolites, we conclude that the importance of the preservation of isolated CuII sites trumps that of Brønsted acid sites for NH3-SCR activity. 相似文献
The simulated annealing method was applied to study the self-assembling process of diblock copolymers in selective solvents for one block. The simulation results illustrated that the morphologies of the copolymer aggregates strongly depend on the interactions between the core-forming blocks and the solvents and on the length of the corona-forming blocks. Multiple morphological transitions were observed in one system. The transition sequence (disordered state-spherical micelles-short rodlike micelles-long rodlike micelles-onionlike aggregates) was observed for copolymers with increasing core-solvent interaction. Similar transitions were observed with the decrease of the length of the corona-forming blocks. The mechanisms of these transitions are investigated. The simulation results are compared with experiments and other simulations. 相似文献
