Preparation and characterization of siliconized epoxy/bismaleimide (N,N′‐bismaleimido‐4,4′‐diphenyl methane) intercrosslinked matrices for engineering applications

Novel hybrid intercrosslinked networks of hydroxyl‐terminated polydimethylsiloxane‐modified epoxy and bismaleimide matrix systems have been developed. Epoxy systems modified with 5, 10, and 15 wt % of hydroxyl‐terminated polydimethylsiloxane (HTPDMS) were developed by using epoxy resin and hydroxyl‐terminated polydimethylsiloxane with γ‐aminopropyltriethoxysilane (γ‐APS) as compatibilizer and dibutyltindilaurate as catalyst. The reaction between hydroxyl‐terminated polydimethylsiloxane and epoxy resin was confirmed by IR spectral studies. The siliconized epoxy systems were further modified with 5, 10, and 15 wt % of bismaleimide (BMI). The matrices, in the form of castings, were characterized for their mechanical properties. Differential scanning calorimetry and thermogravimetric analysis of the matrix samples were also performed to determine the glass‐transition temperature and thermal‐degradation temperature of the systems. Data obtained from mechanical studies and thermal characterization indicate that the introduction of siloxane into epoxy improves the toughness and thermal stability of epoxy resin with reduction in strength and modulus values. Similarly the incorporation of bismaleimde into epoxy resin improved both tensile strength and thermal behavior of epoxy resin. However, the introduction of siloxane and bismaleimide into epoxy enhances both the mechanical and thermal properties according to their percentage content. Among the siliconized epoxy/bismaleimide intercrosslinked matrices, the epoxy matrix having 5% siloxane and 15% bismaleimide exhibited better mechanical and thermal properties than did matrices having other combinations. The resulting siliconized (5%) epoxy bismaleimide (15%) matrix can be used in the place of unmodified epoxy for the fabrication of aerospace and engineering composite components for better performance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 38–46, 2001     

Erasure below glass‐transition temperature of effect of isothermal physical aging in fully cured epoxy/amine thermosetting system

The erasure below the glass‐transition temperature (T_g) of the effect of isothermal physical aging (at aging temperature T_a) in a fully cured epoxy/amine thermosetting system is investigated using the torsional braid analysis (TBA) dynamic mechanical analysis technique and the differential scanning calorimetry (DSC) technique. From the TBA temperature scans, the intensity of the localized perturbation of the moduli in the vicinity of the T_a (90°C), due to isothermal physical aging, is decreased by heating to below the T_g (T_g∞ = 177°C), indicating that the physical aging effect can be eliminated by heating to below the T_g. The isothermal aging effect in the vicinity of the T_a is almost completely eliminated by heating to 50°C above the T_a (i.e., 140°C); however, a competing aging effect occurs above T_a at higher temperatures during the heating. Erasure below T_g of the isothermal physical aging effect is inferred from DSC experiments from the diminished relaxation enthalpy in the vicinity of the T_g, which is measured from the difference in areas between the aged (T_a = 150°C) and deaged thermograms. A comparison of the TBA and DSC results is made. Implications on the heterogeneous nature of the amorphous glassy state of polymers are discussed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 396–404, 2001     

Counter‐ion‐specific helix formation of poly(γ‐methyl L‐glutamate) derivatives containing sulfonate group in aqueous alcohols

Charged polypeptides containing sulfonate groups were prepared by transesterification of poly(γ‐methyl L ‐glutamate) with isethionic acid. The coil–helix transition of the sulfonated polypeptides was investigated in aqueous alcohols. Marked counter‐ion specificity was observed for helix formation: Li⁺ < Na⁺ < Cs⁺ ≦ Rb⁺ ≦ K⁺; this was different to that for poly(L ‐glutamate) (PLG): Cs⁺ ? K⁺ < Li⁺ < Na⁺. Specific helix stabilization by counter‐ion mixing, which has been found for the PLG system, was not observed for the sulfonated polypeptides. The counter‐ion‐ and solvent‐specific helix formation is discussed and compared with that in PLG. © 2001 Society of Chemical Industry     

Electrical,mechanical, structural,and thermal behaviors of polymeric gel electrolyte membranes of poly(vinylidene fluoride‐co‐hexafluoropropylene) with the ionic liquid 1‐butyl‐3‐methylimidazolium tetrafluoroborate plus lithium tetrafluoroborate

Polymeric gel electrolyte membranes based on the polymer poly(vinylidene fluoride‐co‐hexafluoropropylene) [P(VdF–HFP)] with different weight percentages of the ionic liquid (IL) 1‐butyl‐3‐methylimidazolium tetrafluoroborate plus 0.3M lithium tetrafluoroborate (LiBF₄) salt were prepared and characterized by scanning electron microscopy, X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared (FTIR) spectroscopy, complex impedance spectroscopy, pulse echo techniques, and Vickers hardness (H) testing. After the incorporation of the IL plus the salt solution in the P(VdF–HFP) polymer, the melting temperature, glass‐transition temperature (T_g), degree of crystallinity, thermal stability, elastic modulus (E), and hardness (H) gradually decreased with increasing content of the IL–salt solution as a result of complexation between the P(VdF–HFP) and IL. This was confirmed by FTIR spectroscopy. A part of the IL and LiBF₄ were found to remain uncomplexed as well. The ionic conductivity (σ) of the polymeric gel membranes was found to increase with increasing concentration of the IL–salt solution. The temperature‐dependent σs of these polymeric gel membranes followed an Arrhenius‐type thermally activated behavior. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41456.     

表面化学反应控制制备多级结构电极材料及性能

超级电容器和锂离子电池等储能设备的研究和开发日益受到人们的关注。对于超级电容器和锂离子电池等储能设备,其电化学性能主要取决于电极材料,因此高效储能材料的制备成为开发高效储能设备的关键。本文主要介绍了多级结构过渡金属氧化物基电极材料的制备及性能,重点阐述了本实验室近年来在研制高性能超级电容器和锂离子电池方面的相关工作:基于表面化学反应控制制备多级结构金属氧化物、金属氢氧化物/碳嵌入式纳米杂化物以及多种三维结构的多元复合电极材料,表现出优异的电化学性能。     

Direct Staudinger–Phosphonite Reaction Provides Methylphosphonamidates as Inhibitors of CE4 De‐N‐acetylases

De‐N‐acetylases of β‐(1→6)‐D ‐N‐acetylglucosamine polymers (PNAG) and β‐(1→4)‐D ‐N‐acetylglucosamine residues in peptidoglycan are attractive targets for antimicrobial agents. PNAG de‐N‐acetylases are necessary for biofilm formation in numerous pathogenic bacteria. Peptidoglycan de‐N‐acetylation facilitates bacterial evasion of innate immune defenses. To target these enzymes, transition‐state analogue inhibitors containing a methylphosphonamidate have been synthesized through a direct Staudinger–phosphonite reaction. The inhibitors were tested on purified PgaB, a PNAG de‐N‐acetylase from Escherichia coli, and PgdA, a peptidoglycan de‐N‐acetylase from Streptococcus pneumonia. Herein, we describe the most potent inhibitor of peptidoglycan de‐N‐acetylases reported to date (K_i=80 μM ). The minimal inhibition of PgaB observed provides insight into key structural and functional differences in these enzymes that will need to be considered during the development of future inhibitors.     

Transition Metal‐Free Direct C?H (Hetero)arylation of Heteroarenes: A Sustainable Methodology to Access (Hetero)aryl‐Substituted Heteroarenes

In recent years, environmental and economic reasons have motivated the development of transition metal‐free carbon‐carbon bond forming reactions and some excellent reviews have covered this research area of particular interest for the pharmaceutical industry. However, none of these reviews has been specifically dedicated to summarize and discuss the results achieved in the rapidly growing field of the transition metal‐free direct (hetero)arylation reactions of heteroarenes. This review, which covers the literature from 2008 to 2014, aims to provide a thorough insight into the synthetic and mechanistic aspects of these atom economic and environmentally benign reactions also highlighting their advantages and possible disadvantages compared to conventional methods for the synthesis of arylheteroarenes and biheteroaryls via transition metal‐catalyzed reactions.

     

Phase Transitions of Nonionic Surfactant C18:1E10 in Mixed Media of Water with Ionic Liquids

Complicated temperature‐induced phase transitions were shown in two hexagonal liquid crystal mesophases constructed by nonionic surfactant C_18:1E₁₀ in the media of water with ionic liquids, 1‐butyl‐3‐methylimidazolium tetrofluoroborate (bmim‐BF₄) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate (bmim‐PF₆), respectively. Detailed phase transition information was extracted from rheological, polarized optical microscopy, deuterium magnetic resonance spectroscopy and small‐angle X‐ray scattering measurements, with good agreement among these techniques. It is shown that the order‐to‐disorder phase transition occurred in a narrow range of temperatures for both the two hexagonal mesophases. In particular, the mesophases experienced a biphasic hexagonal‐lamellar coexisting before completely melting, which was not found in the corresponding aqueous hexagonal system of the same surfactant concentration. Of most importance, the two target mesophases exhibited some clearly different behaviors. The phase transition temperature is much higher (ca. 10 °C) in a (water + bmim‐BF₄) system than in a (water + bmim‐PF₆) system. After melting, a fast transition from elastic micelle to Newtonian fluid was observed in the (water + bmim‐BF₄) system, while the micelle related to the (water + bmim‐PF₆) system remained elastic over a relatively wide temperature region. The results obtained give a better insight of how the mixed solvents support mesophase formation and modulate the phase transition.     

Electric field tunable thermal stability of energy storage properties of PLZST antiferroelectric ceramics

The electrical hysteresis behaviors and energy storage performance of Pb_0.97La_0.02(Zr_0.58Sn_0.335Ti_0.085)O₃ antiferroelectric (AFE) ceramics were studied under the combined effects of electric field and temperature. It was observed that the temperature dependence of recoverable energy density (W_re) of AFE ceramics depends critically on the applied electric field. While W_re at lower electric fields (<8 kV/mm) shows increasing tendency with increasing temperature from 20°C to 100°C, W_re at higher electric fields (>8 kV/mm) demonstrates decreasing dependence. There exists an appropriate electric field (8 kV/mm) under which the AFE ceramics exhibit nearly temperature‐independent W_re (the variation is less than 0.5% per 10°C). The underlying physical principles were also discussed in this study. These results indicate that the temperature dependence of W_re of AFE materials can be tuned through selecting appropriate electric fields and provide an avenue to obtain thermal stable energy storage capacitors, which should be of great interest to modern energy storage community.