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991.
In this paper, we study a generalized Nicholson??s Blowflies model with feedback control and multiple time-varying delays. Under proper conditions, we employ a novel proof to establish some criteria to guarantee the global exponential convergence and permanence of this model. Moreover, we give two examples to illustrate our main results. 相似文献
992.
Effect of Polymerizable Photoinitiators on the UV‐polymerization behaviors of photosensitive polysiloxane 下载免费PDF全文
Bo Jiang Tong Zhang Liwei Zhao Zhiming Xu Yudong Huang 《Journal of polymer science. Part A, Polymer chemistry》2017,55(10):1696-1705
In this contribution, three polymerizable benzophenone photoinitiators containing maleimide group including 4‐maleimidebenzophenone (MBP), 4‐chlorine‐4′‐maleimide benzophenone (CMBP), and 4‐maleimide‐4′‐[(4‐maleimide)thiophenyl]benzophenone (MMTBP) were designed and synthesized to enhance the polymerization degree of photosensitive polysiloxane containing methacryloxy active groups (MAPSO). The polymerization behaviors of the MAPSO cured by different photoinitiators were investigated using Fourier transform infrared (FTIR). It was noted that the MAPSO initiated by MMTBP showed a high carbon–carbon double bond conversion above 80% because of the existence of thiophenyl group which could generate more radicals from the photolysis reaction at the C? S bond. In addition, the thermal stability of the UV‐cured MAPSO were studied by thermogravimetric analysis (TGA), the result showed that the initial 5% mass loss (T 5%) and residual weight percent at 800 °C in nitrogen of the UV‐cured MAPSO initiated by MMTBP systems was 200 °C and 33.8%. Thus, this work provides a new perspective and efficient strategy to improve the polymerization degree of UV‐curable polysiloxanes with carbon–carbon double bonds. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1696–1705 相似文献
993.
Ying-Xia Wang Chuan-Fei Liu Man-Li Yang Xi-Hui Zhao Zhi-Xin Xue Yan-Zhi Xia 《中国化学快报》2017,28(1):60-64
Concave nanostructures may be developed to improve the specific mass activity of a catalyst for formic acid and methanol electro-oxidation. In this work, we report the elctrocatalytic oxidation of methanol and formic acid in acid medium over concave Pt-Cu-Fe ternary nanocubes (NCs), obtained by the galvanic exchange of Pt and Fe on Cu NCs. The concave Pt-Cu-Fe NCs exhibited improved electrooxidation performance contrasted to Pt-Cu NCs and purchased commercial Pt/C as demonstrated by their improved durability, lower onset potential, and more preferable anti-poisoning properties. These properties are believed to originate from the tailored concave structure of the catalyst and possible synergetic effects among the components of the Pt-Cu-Fe NCs. 相似文献
994.
A novel inorganic-organic hybrid supramolecular compound,[(3-nitroanilinium~+)(18-crown-6)][IO_4](CH_3OH)(1),was discovered as phase-transition materials displaying dielectric anomalous behaviors.The yellow block crystal formed by N-H…O hydrogen bonding that made contact through the cavity of 18-crown-6 was characterized by single-crystal X-ray diffraction,elemental analysis,infrared analysis,thermogravimetric analysis,differential scanning calorimetry,and potential-energy calculations.Differential scanning calorimetry measurements indicate that the compound experiences a reversible phase transition at around 220 K.Temperature-dependent dielectric measurements further confirm the phase transitions.Potential-energy calculations demonstrate that the phase transition occurs due to the molecular order-disorder rotation of CH_3OH,whereas the space grouping of the crystal remains unchanged. 相似文献
995.
Guang Huang Hui-Ran Zhao Qing-Qing Meng Wen Zhou Qi-Jing Zhang Jin-Yun Dong Jia-Hua Cui Shao-Shun Li 《中国化学快报》2017,28(7):1553-1558
6-Substituted 5,8-O-dimethyl-1,4-naphthoquinones (6-DMNQ), the promising anticancer scaffolds, were selectively generated by oxidative demethylation of 2-substituted 1,4,5,8-tetramethoxynaphthalenes with CAN in EtOAc/H2O in comparatively high yields. An interesting finding was that apart from the reported electron-withdrawing effects of substituents on position 2 of naphthalene ring, regioselective synthesis of 6-DMNQ was largely dependent on the steric effects in CAN-mediated oxidation. The selective cytotoxicities of 6-DMNQ from the in vitro cell-based assays were exhibited between the cancer cells and normal cells. Moreover, most of sulfur-containing 6-DMNQ derivatives displayed better anticancer activities than the corresponding oxygen-containing ones, which could provide an available strategy for the design of 6-DMNQ derivatives as potential anticancer agents. 相似文献
996.
Complex new materials from simple chemistry: Combining an amino‐substituted polysiloxane and carboxylic acids 下载免费PDF全文
Yong He Hui Zhao Miao Yao Richard G. Weiss 《Journal of polymer science. Part A, Polymer chemistry》2017,55(23):3851-3861
Changes in rheological, adhesive, and swelling properties of quaternary salts, made by adding one of eight mono‐ or six α,ω‐alkanedioic acids (the latter with two to six or nine carbon atoms) to 6‐7PSil (a polysiloxane with 6%–7% of the monomer units contain a 3‐aminopropyl group) have been correlated with the salt structures. The simple acid‐base chemistry initiates drastic changes in the bulk properties of the materials that depend on the amount and type of the added acid. Thus, the quaternized forms of the 6‐7PSil have significantly enhanced viscoelastic and adhesive properties compared to those of the initial polysiloxane, and they can swell selectively liquids based on their polarity. Also, interpenetrating networks have been made in situ by photopolymerization of salts with vinylic carboxylic acids. DFT calculations on model systems consisting of dimethylammonium α,ω‐alkanedioate salts with two to six carbon atoms provide insights into the interactions responsible for the unexpected dependence of the properties of the 6‐7PSil salts on the chain lengths of the diacids. The potential for applying the methodologies described here to systems with other amino‐substituted polymers and other acid types is noted. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3851–3861 相似文献
997.
998.
Wei Zhao Yi Zhang Xiao Wang Xiaowen Hu Feng Liu Thomas P. Russell Guofu Zhou 《Journal of polymer science. Part A, Polymer chemistry》2018,56(20):1369-1375
Block copolymer (BCP) films with long-range lateral ordering and orientation are crucial for many applications. Here, we report a simple, versatile strategy based on a solution casting procedure, to produce millimeter thick film of BCPs with highly oriented nanostructures. Transmission electron microscope (TEM), small angle X-ray scattering (SAXS), and Hansen solubility parameters were used to study the morphology and interactions of the system. A variety of BCP-solvent pairs were investigated. Factors including set-up geometry, BCP characteristics, solvent evaporation, surface tension, and interactions, such as solvent-BCP, solvent-substrate, and BCP-substrate were examined. A mechanism is proposed to describe the observed long-range lateral ordering and orientation in films up to 1 mm in thickness. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1369–1375 相似文献
999.
A one‐pot method for synthesis of reduced graphene oxide‐supported Cu–Cu2O and catalytic application in tandem reaction of halides and sodium azide with terminal alkynes 下载免费PDF全文
Zhuofei Li Hongyan Zhao Huatao Han Jinyi Song Yang Liu Weihao Guo Zhizhong Sun Wenyi Chu 《应用有机金属化学》2018,32(4)
Reduced graphene oxide (RGO)‐supported Cu–Cu2O nanocomposite material (Cu‐Cu2O@RGO) was prepared through a one‐pot reflux synthesis method. The morphology, crystal structure and composition of the prepared Cu‐Cu2O@RGO were characterized using transmission electron microscopy, X‐ray diffraction, and X‐ray photoelectron, infrared and Raman spectroscopies. Cu‐Cu2O@RGO as a heterogeneous catalyst was applied to tandem reactions of halides and sodium azide with terminal alkynes to synthesize effectively 1,4‐disubstituted 1,2,3‐triazoles. Moreover, the catalyst showed excellent recyclability performance with very little leaching of the metal. Compared with homogeneous catalysts, Cu‐Cu2O@RGO as a green and efficient catalyst was recoverable, easy to separate and highly stable in the tandem method for the synthesis of 1,2,3‐triazole compounds. 相似文献
1000.