Functional materials with excellent electrical and magnetic properties have a potential application in most high-tech fields. Here, superparamagnetic graphene–Fe₃O₄ (G–F) nanosheet hybrids are prepared by a facile one-step hydrothermal process, which will beneficial to well combine with various polymer matrix to get binary functional composites. Polydimethylsiloxane (PDMS) nanocomposites filled with G–F nanosheets are prepared by a three rolling method. The microstructures of G–F nanosheets as well as the electrical, piezoresistive, and magnetic properties of the G–F/PDMS nanocomposites are investigated. Slightly above the percolation threshold (    f_c = 3.4 wt%), the G–F/PDMS nanocomposites with 3.65 wt% of G–F nanosheets show a high conductivity, which is about 10 orders of magnitudes higher than that of pure PDMS, showing an obvious insulator–semiconductor transition. Moreover, the resistance of the nanocomposites with G–F filler near the percolation threshold exponentially increases with the uniaxial pressure. The normalized resistance (R/R₀) can reach up to 870 at 0.88 MPa with 3.65 wt% G–F nanosheets loading. The G–F/PDMS nanocomposites also show superparamagnetism with saturation magnetization values of 0.21 emu g⁻¹. These results suggest that the G–F/PDMS nanocomposites in this work provide a new route to fabricate difunctional polymer-based nanocomposites with a potential application as flexible touch sensors.

The S―S bond cleavage plays an important role in affecting the reactivity or biological activities of disulfide-based compounds. With the aid of density functional theory (DFT) calculations, the present study focuses on predicting the S―S bond dissociation energies (BDEs) of disulfides. The range of BDEs of different types of disulfides was constructed for the first time. It was found that the electronic effect (and especially the conjugation effect) of substituents is predominant in determining the S―S bond strength of disulfides. By contrast, the steric effect is insignificant for most molecules due to the long S―S bond distances. We hope that the present study will benefit the future development of more powerful strategies in activating the S―S bond of disulfides. Copyright © 2015 John Wiley & Sons, Ltd.

The properties of the polymer nanocomposites (PNCs), consisting low density polyethylene (LDPE) and magnesium oxide nanoparticles (MgO-NPs), were systematically discussed in this paper. The shear mixing time and MgO concentration were considered as the two factors affecting the dispersion state, which was found to be effective to change the crystallinity and the mechanical performance of MgO/LDPE PNCs. A reduction in the dynamic shear viscosity was observed when the concentration of MgO-NPs at a relative low level, which was also dominant by the dispersion states of MgO-NPs. Evident enhancement of the static yield stress was revealed only by introducing a minute amount of MgO-NPs (0.25 wt %). Meanwhile, the elastic and loss modulus were also found to be dependent on the dispersion state of MgO-NPs. A positive increase in dielectric permittivity was identified by uniaxial stretching the MgO/LDPE PNCs strips owing to the orientation enhancement of internal microstructure. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43038.

As an excellent alternative to native chemical ligations, the ligation–desulfurization strategy enables the ligations on the other N-terminal peptides (in addition to Cys) and is highly promising in peptide synthesis. In the present study, the relative facility of the desulfurization on the pre-sulfurized amino acids and their carboxylate derivatives has been examined with the aid of density functional theory calculations. It is found that the C–SH bond strengths of the sulfurized amino acids directly relate to the stability of the formed radical. By contrast, the carboxylation of the sulfurized amino acids greatly stabilizes the carbonyl radical center, and both the steric and electronic effects are important factors in determining the C–SH bond strength of the carboxylate precursors. Copyright © 2015 John Wiley & Sons, Ltd.

Polymer composites with polystyrene (PS) as matrix and (Ba_0.5Sr_0.4Ca_0.1)TiO₃ (BSCT) as fillers are prepared by solution casting method. It is found that the dielectric constant of the prepared BSCT/PS composites increases with increasing filler content over the frequency range from 100 Hz to 500 MHz. And the dielectric properties of the composites show a good temperature independency over the range of −30°C to 80°C. For the composite with 50 vol % filler content, the dielectric constant and dielectric loss are comparable with the literature values reported for other PS composites used for microwave substrate. Several theoretical models are used to compare with the experimental data of the dielectric constant of the composites. The microstructure and thermal properties of the composites were also studied. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41398.

Reduced sedimentation of barium titanate (BaTiO₃, BT) nanoparticles during solution casting to prepare the BT/poly(vinylidene fluoride) (PVDF) films is systematically investigated by surface modification of the BT nanoparticles. The surface of BT nanoparticles is hydroxylated by hydrogen peroxide (H₂O₂) or aminated by γ-aminopropyl triethoxysilane (γ-APS). It is found that the compatibility between the fillers and polymer matrix is remarkably improved by such surface treatments. As a result, the agglomeration and sedimentation of BT nanoparticles in the BT/PVDF composite films are significantly reduced, which is supported by morphology observation. Better dielectric properties such as higher dielectric constant, higher breakdown strength, and lower dielectric loss are also obtained for the composite films with surface-modified fillers than those with raw fillers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42662.

Immiscible polymer blends with high dielectric constant (ε) and improved breakdown strength (E_b) performance were obtained by composing poly(vinylidene fluoride) (PVDF) with low-density polyethylene (LDPE) or the LDPE grafted with maleic anhydride (LDPE-g-MAH) through melt-blending way. The dielectric properties of these blends were emphasized for considering the compatibility effect on the energy storage application. Interface morphology, co-continuity behavior, and grafted ratio were simultaneously investigated to detect the compatibility enhancement after introducing MAH. Results showed that the MAH positively improved the dielectric properties. Both the measured E_b of PVDF/LDPE and PVDF/LDPE-g-MAH blends showed a minimum value at v^PVDF = 50 vol % because of the worst compatibility; meanwhile, higher E_b of PVDF/LDPE-g-MAH than that of PVDF/LDPE blend was observed owing to the better compatibility. For considering the effect interface morphology on the dielectric performance, layer-structure films composing with pure PVDF and LDPE layers were further constructed and studied. It was revealed that the layered structure could be treated as a helpful way to improve ε and E_b for immiscible polymer blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42507.

We report an in situ thermal reduction of graphene oxide (GO) in a styrene–ethylene/butylene–styrene (SEBS) triblock copolymer matrix during a melt-blending process. A relatively high degree of reduction was achieved by melt-blending premixed GO/SEBS nanocomposites in a Haake mixer for 25 min at 225 °C. Infrared spectral results revealed the successful thermal reduction of, and the strong adsorption of SEBS on, the graphene sheets. The glass transition temperature of polystyrene (PS) segments in SEBS was enhanced by the incorporation of thermally reduced graphene oxide (TRGO). The resultant TRGO/SEBS nanocomposites were used as a masterbatch to improve the mechanical properties of PS. Both the elongation at break and the flexural strength of PS/SEBS blends were enhanced with the addition of the TRGO. Our demonstration of the in situ thermal reduction of GO via melt blending is a simple, efficient strategy for preparing nanocomposites with well-dispersed TRGO in the polymer matrix, which could be an important route for large-scale fabrication of high-performance graphene/polymer nanocomposites. © 2013 Society of Chemical Industry

Polypropylene-graft-reduced graphene oxide (PP-g-rGO) was synthesized and used as a novel compatibilizer for PP/polystyrene (PP/PS) immiscible polymer blends. SEM observation revealed an obvious reduction of the average diameter for the dispersed PS phase with the addition of PP-g-rGO into a PP/PS (70/30, w/w) blend. The compatibilization effect of PP-g-rGO will subsequently lead to the enhancement of the tensile strength and elongation at break of the PP/PS blends. The compatibilizing mechanism should be ascribed to the fact that PP-g-rGO can not only adsorb PS chains on their basal planes through π-π stacking but also exhibit intermolecular interactions with PP through the grafted PP chains. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40455.

Patterned polymer surfaces with contrasting wettability are prepared by polydopamine (PD) modification. The fabrication process involves spraying dopamine solution droplets on hydrophobic polymer surfaces and PD deposition derived from the oxidative polymerization of dopamine. Each dopamine solution droplets functions as microreactor leading to the formation of patterned PD thin films on the solid/liquid interfaces. Multiple kinds of polymer substrates, including polypropylene, polystyrene, polycarbonate, polyethylene and polytetrafluoroethylene, are endowed with PD patterns using this method. Two types of wetting behaviors are achieved in relation to the micro morphology of the substrates. If smooth or porous substrates are used, the as-formed film exhibited hydrophilic-hydrophobic pattern. When a hierarchical-structured film is used, the uncoated and coated regions have similar static wettability but different dynamic wetting behavior. This PD modification method is also proved to be suitable for flexible and curved surfaces. The results along with the fact that PD could deposit on virtually any surfaces makes this method find wide practical applications in many fields. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41057.

In this work, self-assembly method was used to improve the dielectric constant of triblock copolymers. A series of ABA triblock copolymers with a defined length of poly(n-butyl acrylate) (PBA, B block) segment and different lengths of liquid crystalline (LC) poly[11-(4-cyano-4′-biphenoxy)undecyl methacrylate] (P11CBMA, A block) segments were synthesized by using the atom transfer radical polymerization method. The well-defined triblock copolymers P11CBMA_m-b-PBA_n-b-P11CBMA_m possess three different B/A ratios (n = 50, m = 17, 43, 53). Due to the supramolecular cooperative motion effect, the copolymers can form worm-like microstructure (W_LC = 52.8%), cylinder-like nanostructure with P11CBMA phase embedded in PBA matrix (W_LC = 73.9%), and wide stripe structure with LC domains distributed unevenly in a continuous PBA matrix (W_LC = 77.7%) after annealed at 160°C (above T_i) under N₂ for 24 h, respectively. In order to study the influence of microphase separated morphology of triblock copolymer on the dielectric properties, solvent annealing was also used to develop various nanostructures. After thermal or solvent annealing, the dielectric constants of block copolymers increased dramatically while their loss factors remained the same. For different block copolymers, the dielectric constants increased with the increase of the LC block length. For diverse treatments, dielectric permittivities of samples varied widely with different nanostructures. The results show that the dielectric constants of block copolymers could be tuned by the block ratios and the self-assembled microstructures. These findings will inspire researchers using self-assembly method to design and develop novel flexible materials with high dielectric permittivity. Copyright © 2014 John Wiley & Sons, Ltd.

A mechanistic study was performed on the Rh-catalyzed stereoselective CC/CH activation of tert-cyclobutanols. The present study corroborated the previous proposal that the reaction occurs by metalation, β-C elimination, 1,4-Rh transfer, CO insertion, and a final catalyst-regeneration step. The rate-determining step was found to be the 1,4-Rh transfer step, whereas the stereoselectivity-determining step did not correspond to any of the aforementioned steps. It was found that both the thermodynamic stability of the product of the β-C elimination and the kinetic feasibility of the 1,4-Rh transfer and CO insertion steps made important contributions. In other words, three steps (i.e., β-C elimination, 1,4-Rh transfer, and CO insertion) were found to be important in determining the configurations of the two quaternary stereocenters.

Study of flexible nanodielectric materials (FNDMs) with high permittivity is one of the most active academic research areas in advanced functional materials. FNDMs with excellent dielectric properties are demonstrated to show great promise as energy-storage dielectric layers in high-performance capacitors. These materials, in common, consist of nanoscale particles dispersed into a flexible polymer matrix so that both the physical/chemical characteristics of the nanoparticles and the interaction between the nanoparticles and the polymers have crucial effects on the microstructures and final properties. This review first outlines the crucial issues in the nanodielectric field and then focuses on recent remarkable research developments in the fabrication of FNDMs with special constitutents, molecular structures, and microstructures. Possible reasons for several persistent issues are analyzed and the general strategies to realize FNDMs with excellent integral properties are summarized. The review further highlights some exciting examples of these FNDMs for power-energy-storage applications.

The dielectric properties, elastic modulus, and electromechanical responses of dielectric elastomers (DEs) consisting of silicone rubber and carbon black (CB) incorporated with BaTiO₃ (BT) were studied. When compared with single filler/rubber composites, the resulting three-component nanocomposites yielded very abnormal phenomena. They might be attributed to the interactions between the two kinds of fillers. The increase in concentration of CB (BT) would play a destructive role to the network structure formed by BT (CB) particles. The maximum electromechanical strain of the nanocomposites achieved at mass fraction m_CB = 0.03 and m_BT = 0.06. The resultant electromechanical strain would be attributed to the large dielectric permittivity in the three-component nanocomposites, in which the BT particles themselves have a high dielectric permittivity and the electrical networks of CB particles have a contribution on the increase in dielectric permittivity of the three-component nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A systematic theoretical study has been performed on the recently reported Rh^I-catalyzed [3+2+2] carbocyclization reactions between alkenylidenecyclopropanes (ACPs) and alkynes. With the aid of theoretical calculations, two possible mechanisms, that is, alkene-carbometalation-first and alkyne-carbometalation-first mechanisms, are examined in this study. In the oxidative addition step, the possibility of reaction on either the distal or proximal CC bond of the cyclopropane group has been evaluated. The calculations indicate that the alkene-activation-first mechanism is more favored for the overall catalytic cycle. This mechanism involves four steps, that is, oxidative addition of the distal (rather than the proximal) CC bond of cyclopropane group, alkene carbometalation, alkyne carbometalation, and reductive elimination. The rate-determining step in the overall catalytic cycle is the carbometalation of the alkyne (i.e., the alkyne-insertion step) and this step also determines the regioselectivity. Finally, the origin of the regioselectivity is determined by the steric effect (i.e., the steric crowding between the electron-withdrawing group on alkyne and other ligands on the rhodium center) in the alkyne-insertion step.

Thermosetting conductive adhesive (TCA) comprised of epoxy resin E-51 as matrix, Cu microparticles and nanoparticles modified by silane coupling KH550 as conductive fillers, polyamide resin with low molecular weight as curing agent, and some other additives. It was reported creatively a new liquid curing agent, which solved successfully some difficult problems during preparation of TCA, such as limit of quantity of conductive fillers. Therefore, application of this liquid curing agent decreased greatly the resistivity of TCA under the condition of keeping enough adhesion strength. Antioxidized and mixed Cu particles were developed as conductive fillers in place of expensive Ag. The results showed that optimum conditions of conductive adhesive composed of 16 wt % of epoxy resin E-51, 8 wt % polyamide resin, 65 wt % of Cu microparticles and nanoparticles, 1.3 wt % of silane coupling agent, and 9 wt % of other additives with curing time for 4 h at 60°C. The adhesion strength reached 16.7 MPa and the bulk resistivity was lower than 3.7 × 10⁻⁴ Ω cm. The variation of bulk resistivity was less than 15% at high temperature (100°C). © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012