On the Synthesis,Characterization and Reactivity of N‐Heteroaryl–Boryl Radicals,a New Radical Class Based on Five‐Membered Ring Ligands

The synthesis and physical characterization of a new class of N‐heterocycle–boryl radicals is presented, based on five membered ring ligands with a N(sp²) complexation site. These pyrazole–boranes and pyrazaboles exhibit a low bond dissociation energy (BDE; B?H) and accordingly excellent hydrogen transfer properties. Most importantly, a high modulation of the BDE(B?H) by the fine tuning of the N‐heterocyclic ligand was obtained in this series and could be correlated with the spin density on the boron atom of the corresponding radical. The reactivity of the latter for small molecule chemistry has been studied through the determination of several reaction rate constants corresponding to addition to alkenes and alkynes, addition to O₂, oxidation by iodonium salts and halogen abstraction from alkyl halides. Two selected applications of N‐heterocycle–boryl radicals are also proposed herein, for radical polymerization and for radical dehalogenation reactions.     

Cationic Vesicles Based on Amphiphilic Pillar[5]arene Capped with Ferrocenium: A Redox‐Responsive System for Drug/siRNA Co‐Delivery

A novel ferrocenium capped amphiphilic pillar[5]arene (FCAP) was synthesized and self‐assembled to cationic vesicles in aqueous solution. The cationic vesicles, displaying low cytotoxicity and significant redox‐responsive behavior due to the redox equilibrium between ferrocenium cations and ferrocenyl groups, allow building an ideal glutathione (GSH)‐responsive drug/siRNA co‐delivery system for rapid drug release and gene transfection in cancer cells in which higher GSH concentration exists. This is the first report of redox‐responsive vesicles assembled from pillararenes for drug/siRNA co‐delivery; besides enhancing the bioavailability of drugs for cancer cells and reducing the adverse side effects for normal cells, these systems can also overcome the drug resistance of cancer cells. This work presents a good example of rational design for an effective stimuli‐responsive drug/siRNA co‐delivery system.     

Silica aerogel–poly(ethylene‐co‐vinyl acetate) composite for transparent heat retention films

Poly(ethylene‐co‐vinyl acetate) (EVA) plastic films are widely used for solar coverings including photovoltaic modules and commercial greenhouse films, but are poor at controlling heat flow. In this work, silica aerogel (SA) nanogels were examined for preparing transparent heat retention EVA films that block far infrared spectra radiation to maintain heat, without compromising the optical performance of the films. SA nanogels were melt‐mixed using a mini twin‐screw extruder with EVA pellets to form SA/EVA composite, which were pressed into thin films with controlled thickness. The composite films were characterized in terms of optical properties using a variety of analytical methods including FTIR, UV–Vis spectroscopy, electron, confocal, and atomic force microscopy. Both thermicity and thermal conductivity of commercial and experimental SA/EVA films were measured. The results demonstrated that the SA/EVA films gave improved infrared retention compared to commercial thermal plastic films without compromising visible light transmission, showing the potential for this approach in next generation heat retention films. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 927–935     

Polymeric Membranes Containing Phosphorus in the Chain for Solid Polymer Electrolytes

Abstract

Two new series of solid polymer electrolytes (SPEs) based on phosphorus containing (co)polyesters (PPE) and Lithium triflate were obtained. PPEs are composed of phosphonate moeties (cyclohexyldichlorophosphonate (CHDP)) as linking agent and two diols: PEG (6000) and poly(tetramethylene glycol) (PTMG) in PPE I, and PEG (6000) and 4,4′-cyclohexylidenebisphenol (bisphenol Z, BZ) in PPE II. Polycondensation was carried out in solution in the presence of triethylamine (TEA) as scavenger of HCl side product (PPE I–IIa) and in the absence of any acid acceptor (PPE I–IIb). The Limiting Oxygen Index (LOI) and thermal analysis were performed both on polymers and membranes. The ionic conductivity of SPE membranes based on PPE-salt complexes, with various salt concentrations, was investigated at different temperature and ionic transference numbers were determined. Optimum composition was obtained for the polymer which contains in structure only alkyl units and 15% Lithium triflate.     

Comparative study on structure and properties of titanium/silicon mono‐ and co‐doped amorphous carbon films deposited by mid‐frequency magnetron sputtering

The titanium/silicon mono‐ and co‐doped amorphous carbon films were deposited by mid‐frequency magnetron sputtering Ti target, Si target, and Ti80S20 alloy target, respectively. The effects of doped elements on the composition, surface morphology, microstructure, and mechanical and tribological properties of the films were investigated. The results reveal that the ratio of sp³ and sp² carbon bonds of the films is regulated between 0.28 and 0.62 by a combination of Ti and Si dopant. The addition of small amounts of silicon leads to an increase in sp³ bonds and disorder degree of the sp² carbon. The co‐doped film exhibits significantly superior friction performance than the mono‐doped films. The ultra‐low friction (μ < 0.01) was achieved under a load of 2 N in ambient air with 40% RH. By comparing to the mono‐and co‐doped films, it is thought that the sp³/sp² ratio of the films may play a key role for the superlow friction. Copyright © 2013 John Wiley & Sons, Ltd.     

Mechanical properties and degradation studies of poly(D,L‐lactide‐co‐glycolide) 50:50/graphene oxide nanocomposite films

Poly(D,L‐lactide‐co‐glycolide) 50:50 (PLGA)/graphene oxide (GO) nanocomposite films were prepared with various GO weight fractions. A significant enhancement of mechanical properties of the PLGA/GO nanocomposite films was obtained with GO weight fractions. The incorporation of only 5 wt% of GO resulted in an ~2.5‐fold and ~4.7‐fold increase in the tensile strength and Young's modulus of PLGA, respectively. The thermomechanical behaviors of composite films were investigated by dynamic mechanical analysis. Results indicated that the values of T_g and storage moduli of the PLGA/GO composites were higher than those of the pristine PLGA. The improvement in oxygen barrier properties of composites was presumably attributed to the filler effect of the randomly dispersed GO throughout the PLGA matrix. In this work, we also studied in vitro biodegradation behavior. PLGA/GO composite films were hydrolyzed at 37°C for periods up to 49 days. Because of the presence of GO nanosheets, degradation of composite films took place more slowly with increasing GO amounts. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of thermal annealing on the structural and optical properties of maghemite (γ‐Fe2O3) nanoparticle thin films

In this study, maghemite (γ‐Fe₂O₃) nanoparticles were initially synthesized via chemical co‐precipitation and then deposited by spray pyrolysis as thin films on white glass substrates. The thin films were annealed for 8 h at 400, 450, 500, 550, and 600 °C in an oven. The structural studies of maghemite nanoparticles were carried out using X‐ray diffractometer. Structural properties that we investigated by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, SEM, and Energy dispersive X‐ray analysis (EDS). Optical properties of the samples were also investigated by ultraviolet‐visible (UV–vis) spectroscopy. The results showed that maghemite nanoparticles have crystalline structure with domain that increases in size with increasing annealing temperature. The optical band gap values were found to reduce from 2.9 to 2.4 eV with increase in annealing temperature. Copyright © 2015 John Wiley & Sons, Ltd.