Ligand effect in the synthesis of hyperbranched polymers via copper-catalyzed azide-alkyne cycloaddition polymerization (CuAACP)

Copper-catalyzed azide-alkyne cycloaddition polymerization (CuAACP) of AB₂ monomers demonstrated a chain-growth mechanism without any external ligand because of the complexation of in situ formed triazole groups with Cu catalysts. In this study, we explored the use of various ligands that affected the polymerization kinetics to tune the polymers’ molecular weights and the degree of branching (DB). Eight ligands were studied, including polyethylene glycol monomethyl ether (PEG₃₅₀, M_n = 350), tris(benzyltriazolylmethyl)amine (TBTA), 2,6-bis(1-undecyl-1H-benzo[d]imidazol-2-yl)pyridine (Py(DBim)₂), 2,2′-bipyridyl (bpy), 4,4′-di-n-nonyl-2,2′-bipyridine (dNbpy), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), N,N,N′,N″,N″-penta(n-butyl)diethylenetriamine (PBuDETA), and N,N,N′,N″,N″-pentabenzyldiethylenetriamine (PBnDETA). All ligands except PEG₃₅₀ exhibited stronger coordination with Cu(I) than the polytriazole polymer, which freed the Cu catalyst from polymers and resulted in dominant step-growth polymerization with simultaneous chain-growth feature. Meanwhile, the use of PEG₃₅₀ ligand retained the confined Cu in the polymer, demonstrating a chain-growth mechanism, but lower polymer molecular weights as compared with the no-external-ligand polymerization. Results indicated that aliphatic substituent groups on ligands had little effect on the molecular weights and DB of the polymers, but rigid aromatic substituent groups decreased both values. By varying the ligand species and amounts, hyperbranched polymers with DB value ranging from 0.53 ([TBTA]₀/[Cu]₀ = 5) to 0.98 ([PMDETA]₀/[Cu]₀ = 2) have been achieved. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2238–2244     

Fluorescent carbon nanoparticles: A low-temperature trypsin-assisted preparation and Fe sensing

In recent years, extensive researches are focused on the fluorescent carbon nanoparticles (CNPs) due to their excellent photochemical, biocompatible and water-soluble properties. However, these synthesis methods are generally suffered from tedious processes. In this paper, fluorescent carbon nanoparticles are synthesized by a facile, one-pot, low-temperature method with trypsin and dopamine as precursors. The synthesis process avoids any heating operation and organic solvent, which provides a “green” and effective preparation route. The obtained CNPs exhibit excellent water-solubility, salt-tolerance and photostability. Based on the synergistic action of the inner filter effect and static quenching mechanism, the CNPs are exploited as a “turn-off” fluorescence sensor for sensitive and selective detection of Fe³⁺ ions. The probe shows a wide linear range from 0.1 to 500 μM, with a limit of detection of 30 nM. Furthermore, the as-fabricated fluorescent sensing system is successfully applied to the analysis of Fe³⁺ in biological samples such as human urine and serum samples with satisfactory recoveries (92.8–113.3%).     

Performance improvement of electrochromic display devices employing micro-size precipitates of tungsten oxide

In this paper, we studied the effect of micro-size WO₃ precipitates on the electrochromic characteristics based on aging test. The electrochromic mechanism can be effectively investigated by a solid-state TaN/WO₃/ITO capacitor. The experimental results reveal that WO₃ electrochromic devices with optimized aging time of 4 days exhibit a higher optical contrast and longer retention time, which is mainly attributed to the formation of micro-size WO₃ precipitates during aging process. The performance improvement using micro-size WO₃ precipitates has the potential in future large-area window or energy efficient display applications.     

Site-selective C–H nitration of N-aryl-7-azaindoles under palladium(II) catalysis

The site-selective C–H nitration reaction of 7-azaindoles with t-butyl nitrite under palladium catalysis is described. This protocol provides an efficient method for the construction of ortho-nitrated N-aryl-7-azaindoles with excellent site-selectivity and functional group compatibility. The formed 7-azaindole derivatives can be readily transformed into 7-azaindoles containing an aniline functional group under palladium-catalyzed hydrogenation conditions.     

Experimental Study of Liquid Hydrocarbons Pyrolysis to Acetylene in H2/Ar Plasma

Liquid hydrocarbons including n-hexane, cyclohexane and toluene are pyrolyzed in H₂/Ar plasma to investigate the effects of feedstock properties and key operating conditions (e.g., the feedstock specific input power and residence time) on the reaction performance. The experiments verify that the non-aromatic hydrocarbons show better chemical reactivity than partially aromatic substances. Meanwhile, the straight-chain alkanes and cycloalkanes have better yields of ethylene during the pyrolysis. The results also demonstrate that the pyrolysis reactions are almost completed within the first 0.8?ms in Ar/H₂ plasma independent of the feed substances (i.e., liquid hydrocarbons), where the increased feedstock specific input power enhances the reactant conversions and correspondingly raises the yields of acetylene. At a feedstock specific input power of 4.7?×?10⁴?kJ/kg, the n-hexane conversion is over 90?% and the yield of acetylene reaches 70?%. In addition, when using n-hexane as the feedstock, very little coke is formed during the course of reaction. Comprehensive comparisons of the current experiments with the data reported in the literature are made to point out the key influencing factors, i.e., the effective mass ratio of C/H (R _C/H) in the gaseous phase and the quench temperature. Both two factors would need to be enhanced in order to get a better performance. Finally, the improvements on the specific energy requirement of this process are discussed.     

Room-temperature multiferroic properties of Co-doped KNbO3 ceramics

KNb_0.95Co_0.05O₃ (KN–Co) ceramic was prepared via a solid-state reaction method, and the effect of cobalt dopant on the structural, electric, and magnetic properties was studied. The KN–Co ceramic with polycrystalline perovskite structure exhibited ferromagnetic and ferroelectric properties simultaneously at room temperature, and the coupling of them was confirmed by a large magnetocapacitance effect (about 13%) near the Curie temperature. The possible causes for the magnetism and magnetoelectric properties are discussed.     

Stochastic SIRS model under regime switching

We propose a new stochastic SIRS model under regime switching in which both white and color environmental noises are taken into account. We show that white noise suppresses explosions in the model and the disease-free equilibrium of the model is stochastically asymptotically stable under certain conditions. Moreover, we show that the model is stochastically ultimately bounded and the moment average in time of the model solution is bounded. An example illustrates the boundedness of the moment average in time of the model solution.