Synthesis of well-defined norbornene–lactone-functionalized polymers via ATRP

Well-defined norbornene–lactone-functionalized polymers were synthesized by atom transfer radical polymerization (ATRP) of 5-methacryloxy-6-hydroxynorbornene-2-carboxylic-6-lactone (MNL) and 5-acryloxy-6-hydroxynorbornene-2-carboxylic-6-lactone (ANL) monomers. The ATRP of MNL initiated by ethyl 2-bromopropionate (EBrP), in both N,N-dimethylformamide (DMF) and o-dichlorobenzene (ODCB) solvents was successfully carried out in the presence of CuCl/CuBr and N,N,N′′,N′′,N′′-pentamethyltriethylenetetramine (PMDETA) at 70 °C. The CuCl/ODCB catalyst system gave rise to a lower M _w/M _n (≦1.20) than CuBr/DMF catalyst system. The ATRP of ANL was feasible in the presence of CuBr and PMDETA at 70 °C but showed lower reactivity than MNL. The resulting polymers were characterized by means of gel permeation chromatography (GPC) and ¹H NMR spectroscopy.     

Synthesis of star poly(N-isopropylacrylamide) by β-cyclodextrin core initiator via ATRP approach in water

Star poly(N-isopropylacrylamide) (PNIPAAm) based on a β-cyclodextrin (β-CD) core macroinitiator was synthesized by means of atomic transfer radical polymerization (ATRP) in water using copper(I)/2,2bipyridyl complex as a catalytic system at temperature above the lower critical solution temperature (LCST) of the PNIPAAm. The macroinitiator was prepared by the transesterification reaction of the (β-CD) with 2-bromopropionyl bromide. The LCST of the samples upshifts slightly when the absolute molecular mass of the star PNIPAAm increases. Over the phase transition, the solutions became bluish opalescent due to formation of a heterogeneous phase system consisting of collapsed polymer particles in water. Atomic force microscopy and dynamic light scattering analyses indicated two populations of self-assembled polymer structure: a larger population and a smaller population. The smaller size suggests to self-assembly of polymer micelles and the large one corresponds to aggregates of polymer micelles or star polymers coupled. Polydispersity of the star PNIPAAm ranged from 1.60 to 4.04 within 15 h of reaction, which was attributed to the collapse of the PNIPAAm chains at temperature above the LCST that causes a decrease of the polymer reactivity. This was also attributed to the star–star coupling that generates twice the value of the polydispersity for any time before 15 h of polymerization.     

Synthesis and characterization of polybenzimidazole–nanodiamond hybrids via in situ polymerization method

Poly[2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI) was polymerized in poly(phosphoric acid) (PPA) with the presence of the pristine nanodiamonds (NDs) (0.2–5 wt %) to fabricate NDs-g-OPBI/OPBI nanocomposites via Friedel–Crafts (F-C) reaction. The OPBI chains were successfully attached to the NDs through F-C reaction between carboxylic acid from OPBI and NDs, which was proved by nuclear magnetic resonance, X-ray photoelectron, and X-ray diffraction. NDs-g-OPBI/OPBI nanocomposites show more homogeneous dispersion than the physical blending containing pristine NDs and OPBI matrix, as showed through scanning electronic microscopy images. The mechanical properties, including Young's modulus, yield strength, and tensile strength are all improved by the introduction of NDs (<1 wt %) without loss of ductility, which overcomes the brittleness brought by the addition of inorganic reinforced agent in traditional composites. Dynamic mechanical analysis results showed that the modulus of the ND-g-OPBI/OPBI nanocomposites was significantly higher than OPBI matrix, and the NDs-g-OPBI/OPBI nanocomposites displayed more pronounced improvement than the physical blending, which could be ascribed to the homogeneous dispersion of NDs particles and the covalent bonding between NDs and OPBI via F-C reaction. Thermogravimetric analysis indicated that all the OPBI nanocomposites containing NDs displayed the improved thermal stability. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of mesoporous SiO2–ZrO2 mixed oxides by sol–gel method

A series of SiO₂–ZrO₂ mixed oxides were prepared by sol–gel method in the presence of directing agent, with variable amounts of ZrO₂ between pure silica and pure zirconia, with the aim to obtain catalytic materials suitable as solid acid catalysts. SiO₂–ZrO₂ mixed oxides differ from the two pure starting oxides. While SiO₂ has a low OH density without peculiar acid character, the introduction of increasing amounts of Zr increases the density of the acid sites in the materials. Furthermore both SiO₂/ZrO₂ molar ratio and drying procedure are able to influence the physico-chemical characteristics (textural properties, acid sites distribution, etc.) of these mixed oxides.     

Synthesis of silica nanoparticles from Vietnamese rice husk by sol–gel method

Silica powder at nanoscale was obtained by heat treatment of Vietnamese rice husk following the sol–gel method. The rice husk ash (RHA) is synthesized using rice husk which was thermally treated at optimal condition at 600°C for 4 h. The silica from RHA was extracted using sodium hydroxide solution to produce a sodium silicate solution and then precipitated by adding H₂SO₄ at pH = 4 in the mixture of water/butanol with cationic presence. In order to identify the optimal condition for producing the homogenous silica nanoparticles, the effects of surfactant surface coverage, aging temperature, and aging time were investigated. By analysis of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, the silica product obtained was amorphous and the uniformity of the nanosized sample was observed at an average size of 3 nm, and the BET result showed that the highest specific surface of the sample was about 340 m²/g. The results obtained in the mentioned method prove that the rice husk from agricultural wastes can be used for the production of silica nanoparticles.     

Synthesis and characterization of boehmitic alumina coated graphite by sol–gel method

Non-wettability property makes graphite a good protecting material against the molten metal and/or slag. Properties like high oxidation potential between 600 and 1200 °C and non-wettability with water at room temperatures limits the usage of graphite in castable refractory applications. In this study, sol–gel method, which is a relatively cheaper process, was used. Boehmitic sol was obtained by hydrolyzing and peptiziting the alkoxide AIP (aluminum isopropoxide) used as alumina source. Then natural flake graphite was mixed with the boehmitic solution for coating of graphite. At 120 °C boehmitic sol coated graphite was dried and gelled. Then heat threaded at 550 °C for γ-Al₂O₃ transformation of boehmite. Products that obtained from the studies were characterized with FTIR and XRD tests. Alumina coated graphite samples were made by repeating the same steps and TG analysis were made to investigate the oxidation behaviour of the samples. Finally, SEM–EDS analyses were carried out to investigate the microscopic properties of the alumina coated graphite powders.     

Hydrodeoxygenation of p-cresol on unsupported Ni–W–Mo–S catalysts prepared by one step hydrothermal method

Unsupported Ni–Mo–W sulfide catalysts were prepared by one step hydrothermal method using ammonium heptamolybdate and thiocarbamide in water, and characterized by X-ray diffraction (XRD), nitrogen physisorption and transmission electron microscopy (TEM). The effect of W/Mo molar ratio on the catalytic performance was studied using the HDO of p-cresol as a probe. The results showed that the Ni–Mo–W–S catalyst with an appropriate W/Mo molar ratio possesses the short slab length of MoS₂ or WS₂ structure and many active sites, leading to the high HDO activity and HYD selectivity.     

Synthesis of nanocrystalline ZnO–NiO mixed metal oxide powder by homogeneous precipitation method

Nanocrystalline ZnO–NiO mixed metal oxide powder has been successfully prepared via a simple homogeneous precipitation method in short time. The nanocrystalline sample was obtained at low calcination temperature (350 °C). Specific surface area, crystallite size and optical band gap of the samples depend on calcination temperature. The synthesized samples were characterized by means of powder X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy, diffuse reflectance spectroscopy, surface area measurements, scanning electron microscopy coupled with energy dispersive X-ray analysis, transmission electron microscopy and magnetic measurements. The synthesized powder samples have been tested for their catalytic reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride.     

Synthesis and characterization of nanocrystalline zinc aluminate spinel powder by sol–gel method

Single-phase nanocrystalline zinc aluminate (ZnAl₂O₄) spinel powder has been synthesized by the sol–gel method. Zinc aluminate nanoparticles were formed at 600 °C, which is at much lower temperature than by solid state reactions. Formation of ZnAl₂O₄ and their particle size depend on the calcination temperature. Calcination temperature also affects the specific surface area and pore volume. The nanocrystalline zinc aluminate was characterized by powder X-ray diffraction, FT-IR spectroscopy, thermal gravimetric analysis, diffuse reflectance spectroscopy, surface area measurements, field emission scanning electron microscopy coupled with energy dispersive X-ray analysis and transmission electron microscopy. Catalytic reactivity of nanocrystalline zinc aluminate was tested for the reduction of 4-nitrophenol to 4-aminophenol using NaBH₄.     

Synthesis of poly(N-vinyl carbazole)-based block copolymers by sequential polymerizations of RAFT–ATRP

Poly(N-vinylcarbazole) (PNVK) is one of the extensively studied photoconductive polymers because of its wide ranges of applications. Through the reversible addition-fragmentation chain transfer/macromolecular design via the interchange of xanthates (RAFT/MADIX) polymerizations, in this study we investigated the syntheses of PNVK-based block copolymers (BCPs) with styrene (St) and methyl methacrylate (MMA). A variety of difunctional haloester-xanthate inifers were prepared and subjected to sequential polymerizations through RAFT and ATRP. In the presence of small amounts of bromoxanthate inifers, the ¹H NMR spectra showed nearly complete consumption of the NVK monomer, but without formation of PNVK. The bromoxanthate inifer could act as acidic moieties that protonated the highly basic NVK monomer. Through ¹H NMR and MALDI-TOF spectroscopic analyses, the structures of byproducts were indentified and a plausible mechanism for their formation was proposed. Alternatively, RAFT/MADIX polymerizations of NVK with two chloroxanthate inifers S-[1-methyl-4-(6-chloropropionate)ethyl acetate] O-ethyl dithiocarbonate and S-[1-methyl-4-(6-chloroisobutyrate)ethyl acetate] O-ethyl dithiocarbonate) provided first-order kinetic plots and well-controlled PNVK-Cl MIs (M_n ≈ 6000–40,000; M_w/M_n < 1.35). Using a suitable ATRP-initiating groups and optimization of the reaction conditions, the BCPs PNVK-b-PSt (M_n ≈ 4900–12,800; M_w/M_n < 1.5) and PNVK-b-PMMA (M_n ≈ 46,000–100,000; M_w/M_n < 1.35) were obtained.     

Synthesis and characterization of mesoporous ZnTiO3 rods via a polyvinylpyrrolidone assisted sol–gel method

Mesoporous ZnTiO₃ rods were fabricated via a polyvinylpyrrolidone assisted sol–gel method. In this method, the control of nanostructure growth was achieved by the cooperative assembly among precursors and polyvinylpyrrolidone, through which well-designed one-dimensional morphology and mesoporosity could be obtained. The regularity of rod-like morphologies was sensitive to cooperative assembly temperature. Furthermore, the mesoporous ZnTiO₃ rods were used for photodegradation of organic dyes and proved to be useful photocatalysts with excellent reusability thanks to the well-designed nanostructure and one-dimensional structure. Hence mesoporous ZnTiO₃ rods with good photocatalytic activity and low cost could offer broad opportunities for environmental remediation.     

A generalized sample preparation method by incorporation of metal–organic compounds into polymers for electroless metallization

Polymer metallization is important for several applications but triggering of electroless deposition is problematic. A simple and inexpensive method to prepare the polymers for initiating the electroless copper deposition is successfully applied to Liquid Crystal Polymer and Polyethylene Terephthalate. The samples are prepared by incorporation of a small amount (<0.5 wt%) of metal–organic compounds (palladium, nickel, or copper acetates) in the molten polymers. During blending, the polymers are held at sufficiently high temperatures to thermally decompose the acetates, yielding the metallic particles (Pd, Ni, or Cu) which are used as the activators. After surface preparation, copper is deposited on polymers in an electroless bath including formaldehyde as reducer. The influence of bath parameters (temperature, composition) and the nature of activators is investigated. This method can be extended to other polymers by finding an appropriate polymer/metal–organic couple. It is also demonstrated that cheaper Ni or Cu can substitute expensive Pd.     

Synthesis and characterization of bioactive molecules grafted on poly(?-caprolactone) by “click” chemistry

A facile and efficient strategy to graft bioactive molecules (nicotinic acid, p-aminobenzoic acid, and phthaloyltryptophan) onto poly(?-caprolactone) (P(?CL)) was achieved by copper-catalyzed Huisgen’s 1,3-dipolar cycloaddition known as click reaction. P(αCl?CL), with 10, 20, and 30% of α-chloro-?-caprolactone (αCl?CL) units were copolymerized by ring opening polymerization using ?CL and αCl?CL as starting materials in the presence of 1,4-butanediol and Sn(Oct)₂. Subsequently, the chloride pendent was converted to azide followed by cycloaddition with terminal alkyne derivatives of the aforementioned bioactive molecules. The complete addition was accomplished at all ratios. The characteristic molecular features of these copolymers were evaluated by FTIR, NMR, and GPC. Thermal analysis data indicated that the grafted compounds led to polymorphic alteration and different pattern of thermal degradation depending on the molecular structure and the size of the grafted compounds. They are the basis for further development of grafted copolymer as drug delivery carriers.     

Ionic strength effect in polyelectrolyte dilute solutions within the Debye–Hückel approximation: Monte Carlo and Brownian dynamics simulations

Two chain models, a Gaussian chain and a touching-beads (wormlike) chain, are used to represent a flexible polyelectrolyte (sodium polystyrene sulfonate) and a semiflexible polyelectrolyte (sodium alginate), respectively. Monte Carlo and Brownian dynamics simulations of those models were carried out to obtain the ionic strength dependence of some conformational and hydrodynamic properties expressed in form of equivalent radii. Electrostatic interactions were taken into account by the Debye–Hückel potential, thus counterions are not considered explicitly. In the case of the sodium polystyrene sulfonate model, a linear dependence of the equivalent radii with the ionic strength is found for a region of intermediate to low enough ionic strength values, whereas for high values of the ionic strength the equivalent radii reach a plateau with a value equal to that of the uncharged chain. Thus, an extrapolation to infinite ionic strength of the linear region would not report the actual property value of the uncharged chain. In the case of the sodium alginate model such a linear dependence is not so clearly appreciated. Our simulation results show a good agreement with several experimental data which support the validity of the Debye–Hückel approximation to model different types of polyelectrolyte solutions in a simple way.     

MECCO: A method to estimate concentrations of condensing organics—Description and evaluation of a Markov chain Monte Carlo application

The development of a new method to estimate concentrations of condensing organics (MECCO) is described. A Markov chain Monte Carlo method is applied, and by using measured particle size distribution and random vapor concentrations as input, the predicted changes in particle population by an aerosol dynamics model are utilized. The method provides the ambient vapor concentrations required for the observed particle growth in particle number size distribution data, assuming all growth can be attributed to net condensation of super-saturated vapors. In this paper, MECCO was coupled with the UHMA box-model to provide aerosol dynamics. With few changes, MECCO could be applied to study other input parameters, and coupled with other dynamics models as well. Evaluation of the method was carried out with simulated output from the UHMA model using the assumption of three organic vapors, and MECCO-UHMA was able to estimate their concentrations with great accuracy. However, the condensation of vapors is currently considered irreversible, since the used particle size distribution data do not provide information on the composition of particles. The distinguishing between the vapors is based on few vapor parameters, which limits the possibilities of identifying actual vapors. An example of atmospheric application is also presented. This revealed the importance of quality control of the input particle concentrations: instrumental noise and changes in the observed air mass pose challenges for the presented method. Data need to be smoothed in a reasonable way so that the point-like measurements can be utilized, but also so that the important information on particle growth is conserved. MECCO is a useful tool to approximate vapor concentrations and may be applied to estimate vapor properties as well. However, a computationally efficient and physically accurate aerosol dynamics model is essential for MECCO's performance.     

Synthesis and optical characterization of Er-doped bismuth titanate nanoparticles grown by sol–gel hydrothermal method

The Er³⁺-doped bismuth titanate (Bi₄Ti₃O₁₂, BIT) nanoparticles were synthesized by a combined sol–gel and hydrothermal method under a partial oxygen pressure of 30 bar. The composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman scattering. They showed pure and homogeneous spherical BIT nanoparticles with a size below the 30 nm. The incorporation of Er ions showed a strong decrease in the lattice parameters, as well as averaged particle size. The photoluminescence up-conversion (excitation wavelength =1480 nm) showed an enhancement of the infrared emission (980 nm) as Er concentration increased, achieving a maximum for 6% mol, while photoluminescence spectra (excitation wavelength =473 nm) showed a strong green emission (529 and 553 nm) with a maximum at 4% mol.     

Synthesis of secondary amine-based fluorescent porous organic polymers via Friedel–Crafts polymerization reaction for adsorbing and fluorescent sensing iodine

We present the preparation and characterization of a novel class of secondary amine-based porous organic polymers (POPs: TDPA and TTPBTA), and their iodine adsorption, fluorescence sensing properties for the first time. Two secondary amine-based POPs were synthetized by Friedel−Crafts polymerization reaction catalyzed via methylsulfonic acid with yields of 22.51 and 54.44%. The thermal stability of resulting POPs run up to above 268 and 568°C, and their BET specific surface areas are 56.5 and 2.49 m² g⁻¹, respectively. Their iodine adsorption and fluorescent sensing properties are comparable to that of triphenylamine (TPA)-based (tertiary amine) POPs. The resulting POPs display excellent sorption abilities to iodine molecules with the iodine adsorption capacity of about 3.93 and 1.64 g g⁻¹. Adsorbed iodine is easily desorbed by heating or washing with organic solvents, which make them reusable. They can also adsorb iodine from cyclohexane solution. Moreover, the POPs possess excellent fluorescent sensing property for I₂ with Ksv of 1.85 × 10⁴ and 6.56 × 10⁴ L mol⁻¹, as well as the limits of detection (LODs) of 1.62 × 10⁻¹¹ and 6.86 × 10⁻¹² mol L⁻¹. The performance of adsorbing and fluorescence sensing iodine can be explained by electron transfer mechanism.     

Synthesis of ultra-fine tantalum carbide powders by a combinational method of sol–gel and spark plasma sintering

Tantalum carbide (TaC) nanopowders were synthesized by a novel method combining the sol–gel and spark plasma sintering (SPS) processes using tantalum pentachloride (TaCl₅) and phenolic resin as the sources of tantalum (Ta) and carbon (C), respectively. Gels of Ta-containing chelate with good uniformity and high stability were prepared by solution-based processing. The products with the structure of carbon-coated tantalum pentoxide (Ta₂O₅) were obtained after pyrolysis at 800?°C. Further heat treatment by SPS resulted in the fast formation of TaC at a relatively low temperature. The effects of the C/Ta molar ratio in the raw materials and the heat treatment temperature on the prepared powders were investigated. With increase in the C/Ta molar ratio from 3.75 to 4.25, the synthesis temperature, oxygen content and average crystallite size of the TaC powders decreased. Furthermore, the oxygen content of the powders prepared at the C/Ta molar ratio of 4.25 could be reduce by increasing the heat treatment temperature from 1400° to 1600°C, which unfortunately also induced a mean crystallite size increase from 30 to 100?nm. The TaC powders obtained at a comparatively low C/Ta molar ratios of 4.25 at 1500?°C had an average particle size of about 50?nm and a low oxygen content of about 0.43?wt%.     

Synthesis of nanosized zirconium carbide powders by a combinational method of sol–gel and pulse current heating

Zirconium carbide nanopowders were synthesized by a novel method combining the advantages of sol–gel method and rapid synthesis using pulse current heating. The core-shelled structure of ZrO₂/C mixture was obtained during the sol–gel process, and further heat treatment in SPS led to the fast formation of ZrC. The particle size of ZrO₂ played an important role in the synthesis of nanosized ZrC powders. In addition, the coalescence and grain growth of ZrC particles could be also limited due to the fast heating rate. As a result, the reactions were thoroughly completed at a relatively low temperature and ZrC nanopowders of 60–100 nm were obtained. The corresponding powders also had low oxygen content (∼0.64 wt%) and residual carbon content (∼0.27 wt%). Additive-free ZrC powders could be sintered to ∼99% relative density with an average grain size of 0.8 μm at low temperature of 1750 °C.     

Synthesis of graphene–CNT hybrids via joule heating: Structural characterization and electrical transport

Graphene–CNT (G/CNT) hybrids were formed via in situ joule heating inside a transmission electron microscope (TEM). The formation of the G/CNT structure was suggested to be induced by the sequential and spontaneous unzipping of the outmost wall of the multi-walled CNT under uniformly thermal etching and voltage pulse of 0.2–1 V. The conductance of the G/CNT hybrids show a significantly change (up to 38 times) after decorated with CdTe quantum dots. Our results suggest the potential use of the G/CNT hybrids for high-sensitivity detections, as well as super capacitors or catalyst matrices given their large specific surface areas.