bluuebunny/crossref_metadata_2025_split huggingface dataset:
A novel negative dielectric constant material based on phosphoric acid doped poly(benzimidazole)
Authors: Gordon Keith L. , Kang Jin Ho , Park Cheol , Lillehei Peter T. , Harrison Joycelyn S. 
Published: February 2012

AbstractMetamaterials or artificial negative index materials (NIMs) have generated great attention because of their unique electromagnetic properties. The main challenge in current NIM development is creating a homogenous NIM without the need of complex geometric architectures consisting of capacitors and inductors or aggregated fillers, but possessing a tunable plasma frequency. A natural material that can exhibit negative values for permittivity and permeability simultaneously has not been found, or discovered. If one can design a negative dielectric constant material with a tunable plasma frequency of interest, implementing negative permeability into the material or system would be much more readily achievable to create a metamaterial. In this regard, a novel negative dielectric constant material, which is an essential key to creating the NIMs, was developed by doping ions into a polymer, a protonated poly(benzimidazole) (PBI). The doped PBI showed a negative dielectric constant at frequencies of kHz to MHz because of its reduced plasma frequency and an induction effect. As temperature increased, the dielectric spectrum changed from a relaxation to a resonance behavior and exhibited a larger magnitude of negative dielectric constant at a lower frequency. The conductivity of the doped PBI measured as a function of both temperature and frequency followed the same trend as the dielectric constant. With respect to the dielectric constant and the conductivity data, it can be assumed that the origin of the negative dielectric constant is attributed to the resonance behavior of the highly mobile ions at elevated temperatures and high frequencies. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Investigation of the stereodefect distribution and conformational behavior of isotactic polypropylene polymerized with different Ziegler–Natta catalysts
Authors: Kang Jian , Yang Feng , Wu Tong , Li Huilin , Liu Dongming , Cao Ya , Xiang Ming 
Published: February 2012

AbstractTwo isotactic polypropylene (iPP) samples (PP‐A and PP‐B) were obtained by utilizing two different heterogeneous Ziegler–Natta catalysts in a given polymerization system. The molecular structure and conformational behavior of the samples were studied. The results of determination of xylene soluble material (XS) and 13C NMR showed that the average isotacticity of the samples were nearly same. However, the results of high‐resolution high‐temperature 13C NMR (HRHT 13C NMR) and successive self‐nucleation and annealing (SSA) fractionation revealed that the amount of high isotacticity of PP‐B was lower than that of PP‐A, and the amount of relative medium and low isotacticity of PP‐B was higher than PP‐A, indicating that the stereodefect distribution of PP‐B was more uniform than PP‐A. The calculation of average meso sequence length from SSA was found to be in good agreement with that calculated from the results of HRHT 13C NMR. Moreover, Fourier transformation infrared was utilized to study the influence of stereodefect distribution on the conformational behavior of iPP. The result suggested that the molecular conformation of the PP‐B was more disordered than PP‐A, the regularity of molecular structure for PP‐B was lower than that of PP‐A. The related action mechanism and the influences of which on crystallization behavior were discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Synthesis and characterization of biodegradable poly(butylene succinate)‐co‐oligo(L‐valine) copolyesters via direct melt transesterification
Authors: Ye Suwen , Tan Licheng , Chen Yiwang , Wei Junchao , Zhou Weihua 
Published: February 2012

AbstractA series of aliphatic biodegradable poly(butylene succinate)‐co‐oligo(L‐valine) (PBSVAL) copolyesters were synthesized with dimethyl succinate, 1,4‐butanediol (BDO), and oligo(L‐valine) (OVL) as reagents. The GPC results show that the weight average molecular weight (Mw) of the copolyester with a feed ratio (PBS/OVL) of 0.9/0.1 (PBSVAL10) is 4.9 × 104 g/mol, and its polydispersity index is 1.68. All the copolyesters were more thermally stable than the pristine poly(butylene succinate) (PBS). The incorporation of valine units into the copolyesters eventually led to the decrease of the crystallization temperature, melting temperature, while increase of crystallization enthalpy and melting enthalpy. The crystal structure of the copolyesters is similar to pure PBS except for higher degrees of crystallinity; also there was a trend to higher degrees of crystallinity with increasing content of valine. From the enzymatic degradation experiment, it is clear that the PBSVAL10 copolyester shows less weight loss as compared to pure PBS which is due to PBSVAL10 with higher degree of crystallinity. The morphology of the copolyester films after degradation was also studied by the scanning electron microscopy. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Synthesis of superporous hydrogels by a postpolymerization foaming protocol and their water absorbent behavior
Authors: Gong Ruiying , Kang Ning , Mu Youbing , Li Jianzhong , Wan Xiaobo 
Published: February 2012

AbstractThe rate of swelling is one of the most important parameters of hydrogel polymeric networks; therefore, the objective of this study was to develop a new method to synthesize superporous poly(acrylic acid‐co‐acrylamide) hydrogels to improve swelling rate. The hydrogel was prepared in the presence of a foaming agent (comprising azodicarbonamide and zinc oxide), using 2,2′‐Azobis[2‐(2‐imidazolin‐2‐yl)propane] dihydrochloride as the initiator. The N2 released during the polymerization led to the formation of a slightly foamed gel; we refer to the process as a prefoaming process. The obtained gel underwent a further foaming process to form a superporous hydrogel. Unlike in existing methods, the consistent time control of the foaming agent addition and the onset of gelling were not necessary in this simplified gel preparation procedure. The water absorbent behavior of the superporous hydrogels suggested that the polymers obtained from the prefoaming process reached the swelling equilibrium more rapidly than those with little prefoaming, and their absorbent capacity was greater. Scanning electron microscope images show that interconnected pores inside these superporous gels formed capillary channels, which are critical for the fast swelling rate. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Preparation and characterization of double‐layered microencapsulated red phosphorus and its flame retardance in poly(lactic acid)
Authors: Chang Shaokun , Zeng Chao , Yuan Weizhong , Ren Jie 
Published: February 2012

AbstractA novel double‐layered microencapsulated red phosphorus (DMRP) has been prepared through chemical precipitation of aluminum trihydrate (ATH) and in situ polymerization of melamine formaldehyde (MF) resin on the red phosphorus (RP) powder surface, and its structure was characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The influence of DMRP on flame retardance and thermal stability of poly(lactic acid) (PLA) was thoroughly investigated by means of X‐ray diffractometry (XRD), limiting oxygen index (LOI), vertical burning test, and thermogravimetric analysis (TGA). With an optimum mass ratio of RP/ATH/MF = 72.25%/12.75%/15%, it has been found that PLA with the addition of DMRP at 25 wt % loading level shows good flame retardance compared to plain RP as well as the conventional microencapsulated red phosphorus (CMRP), and can achieve UL94 V‐0 rating along with an LOI increase from 20.5 to 29.3. The TGA and XRD studies indicate that the interaction occurs among all three components: RP, ATH, and MF resin. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Effect of different rapeseed‐oil‐based polyols on mechanical properties of flexible polyurethane foams
Authors: Rojek Piotr , Prociak Aleksander 
Published: February 2012

AbstractTwo rapeseed‐oil‐based polyols were synthesized by partial epoxidation of the double bonds in fatty acid chains and overall opening oxirane rings by using diethylene glycol. Flexible polyurethane foams with varied isocyanate index and modified by partial substitution of petrochemical polyether triol with rapeseed‐oil‐derived polyols were obtained. Bio‐polyols: Polyol I and Polyol II differed in functionalities (2.5 and 5.2, respectively) and hydroxyl values (114 and 196 mg KOH/g, respectively). Influence of the bio‐polyols on mechanical properties, resilience, apparent density, and cellular structure of synthesized foams was investigated. Compression properties were examined and compared via determining compression values and compression stress—strain characteristics, as well as tensile strength and elongation at break were estimated. Foams modified with Polyol I had higher values of resilience and elongation at break than those with Polyol II, while higher tensile and compression strength and superior cell structure were observed in the case of foams modified with Polyol II. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012
Synthesis and Spectroscopic Properties of Phthalocyanine–[60]Fullerene Conjugates Connected Directly by Means of a Four‐Membered Ring
Authors: Fukuda Takamitsu , Kikukawa Yuu , Takaishi Shiori , Kobayashi Nagao 
Published: February 2012

AbstractNew covalently C60‐conjugated phthalocyanine (Pc) analogues in which the Pc and C60 components are connected by means of a four‐membered ring have been synthesized by taking advantage of a [2+2] cycloaddition reaction of C60 with benzyne units generated from either a phthalocyanine derivative (8) or its precursor (1). The reaction of 1 with PhI(OAc)2 and trifluoromethanesulfonic acid (TfOH) followed by the [2+2] cycloaddition of C60 in the presence of tetra‐n‐butylammonium fluoride (TBAF) yielded the C60‐substituted Pc precursor (3). Mixed condensation of 3 and 4,5‐dibutylsulfonylphthalonitrile (4) in a thermally promoted template reaction using a nickel salt successfully gave the Pc–C60 conjugate (5). Results of mass spectrometry and 1H and 13C NMR spectroscopy clearly indicate the formation of the anticipated Pc–C60 conjugate. Direct coupling of C60 with the Pc analogue that contained eight peripheral trimethylsilyl (TMS) groups (8) also proceeded successfully, such that mono and bis C60‐adducts were detected by their mass, although the isolation of each derivative was difficult. The absorption and magnetic circular dichroism (MCD) spectra of 5 and the reference compound (7) differ from each other in the Q‐band region, thereby suggesting that the presence of the C60 moiety affects the electronic structure of the conjugate. The reduction and oxidation potentials of 5 and 7 obtained by cyclic voltammetry are comparative, except for the C60‐centered reduction couple at −1.53 V versus Fc+/Fc in o‐dichlorobenzene (o‐DCB). A one‐electron reduction of 5 and 7 in tetrahydrofuran (THF) by using the sodium mirror technique results in the loss of band intensity in the Q‐band region, whereas the characteristic marker bands for Pc‐ring‐centered reduction appear at around 430, 600, and 900 nm for both compounds. The final spectral shapes of 5 and 7 upon the reduction resemble each other, thus indicating that no significant molecular orbital (MO) interactions between the C60 and Pc units are present for the reduced species of 5. In contrast, the oxidized species of 5 and 7 generated by the addition of NOBF4 in CH2Cl2 show significantly different absorption spectra from each other. Whereas the broad bands at approximately 400–550 nm of 7+ are indicative of the cationic π‐radical species of metallo‐Pcs and can be assigned to a transition from a low‐lying MO to the half‐filled MO, no corresponding bands were observed for 5+. These spectral characteristics have been tentatively assigned to the delocalized occupied frontier MOs for 5+. The experimental results are broadly supported by DFT calculations.
Synthesis of Olive‐Shaped Mesoporous Platinum Nanoparticles (MPNs) with a Hard‐Templating Method Using Mesoporous Silica (SBA‐15)
Authors: Wang Hongjing , Imura Masataka , Nemoto Yoshihiro , Park Sang‐Eon , Yamauchi Yusuke 
Published: February 2012

AbstractWell‐ordered mesoporous Pt nanoparticles (MPNs) with uniform olive shapes are synthesized by using two‐dimensional (2D) hexagonal mesoporous silica (SBA‐15) as a hard template. The average particle sizes are controllable in the range of 150 to 230 nm by changing the reduction time. Low‐angle XRD profiles for the obtained MPNs show three distinct peaks assignable to the (10), (11), and (20) planes of a highly ordered 2D hexagonal symmetry. From high‐magnification SEM images, periodically arranged Pt nanowires are observed clearly, which are a negative replica of the 2D hexagonally ordered mesoporous silica (SBA‐15). Furthermore, the single crystallinity of the Pt fcc structure coherently extends over the whole particles. As a result of such unique character as well as high surface area, the obtained MPNs show distinctly enhanced electrocatalytic properties for methanol oxidation reaction compared to other Pt samples, such as Pt black.
Accounting for the constrained availability of land: a comparison of bio‐based ethanol, polyethylene, and PLA with regard to non‐renewable energy use and land use
Authors: Bos Harriëtte L. , Meesters Koen P.H. , Conijn Sjaak G. , Corré Wim J. , Patel Martin K. 
Published: February 2012

AbstractIn a bio‐based economy, chemicals, materials, biofuels, and other forms of energy will be produced from biomass. Pressure on agricultural land will thus increase, calling for highly efficient solutions in terms of land use, with minimal environmental impacts. In order to gain better insight into the available options and their trade‐offs, this perspective studies the production of polylactic acid (PLA), bioethanol, and bio‐based polyethylene (PE) from wheat, maize, sugarbeet, sugarcane, and Miscanthus. While in current agricultural practice some plants are harvested and used as whole crop (e.g. Miscanthus), for others only part of the plant is used, with the remainder being returned to the field (e.g. wheat straw). In order to obtain an understanding of the unused potential we assume as default case that all agricultural residues and processing co‐products are used for energy purposes, thereby replacing non‐renewable energy. We conclude that this agricultural practice would allow to substantially reduce non‐renewable energy use (NREU). We also find a clear difference in ranking depending on whether we study (i) NREU per (metric) tonne of product or (ii) Avoided NREU per hectare of land. The latter seems a suitable choice in a world where land availability is limited. In this case, we identify PLA as the preferred choice, irrespective of the type of crop. The production of ethanol for the replacement of fuels scores as the worst option for all crops. For each of the products studied, sugarcane offers the highest savings per hectare followed by sugarbeet. © 2012 Society of Chemical Industry and John Wiley & Sons, Ltd
Electric field and current density distribution in an anatomical head model during transcranial direct current stimulation for tinnitus treatment
Authors: Parazzini Marta , Fiocchi Serena , Ravazzani Paolo 
Published: February 2012

AbstractTinnitus is considered an auditory phantom percept. Recently, transcranial direct current stimulation (tDCS) has been proposed as a new approach for tinnitus treatment including, as potential targets of interest, either the temporal and temporoparietal cortex or prefrontal areas. This study investigates and compares the spatial distribution of the magnitude of the electric field and the current density in the brain tissues during tDCS of different brain targets. A numerical method was applied on a realistic human head model to calculate these field distributions in different brain structures, such as the cortex, white matter, cerebellum, hippocampus, medulla oblongata, pons, midbrain, thalamus, and hypothalamus. Moreover, the same distributions were evaluated along the auditory pathways. Results of this study show that tDCS of the left temporoparietal cortex resulted in a widespread diffuse distribution of the magnitude of the electric fields (and also of the current density) on an area of the cortex larger than the target brain region. On the contrary, tDCS of the dorsolateral prefrontal cortex resulted in a stimulation mainly concentrated on the target itself. Differences in the magnitude distribution were also found on the structures along the auditory pathways. A sensitivity analysis was also performed, varying the electrode position and the human head models. Accurate estimation of the field distribution during tDCS in different regions of the head could be valuable to better determine and predict efficacy of tDCS for tinnitus suppression. Bioelectromagnetics 33:476–487, 2012. © 2012 Wiley Periodicals, Inc.
Site‐Selective Suzuki–Miyaura and Sonogashira Cross Coupling Reactions of the Bis(triflate) of 2,4′‐Bis(hydroxy)diphenyl Sulfone
Authors: Khera Rasheed Ahmad , Ali Asad , Hussain Munawar , Ibad Muhammad Farooq , Villinger Alexander , Langer Peter 
Published: February 2012

AbstractDescribed is the synthesis of novel arylated and alkynylated 2,4′‐diphenyl sulfones based on what are, to the best of our knowledge, the first palladium(0)‐catalyzed cross‐coupling reactions of bis(triflates) of 2,4′‐bis(hydroxy)diphenyl sulfone. The reactions proceed with very good site‐selectivity.
Mg‐Silicate Carbonation Based on an HCl‐ and NH3‐Recyclable Process: Effect of Carbonation Temperature
Authors: Zhang J. , Zhang R. , Geerlings H. , Bi J. 
Published: February 2012

AbstractA new indirect mineral carbonation process is studied which could mitigate anthropogenic CO2 emissions. In this process, magnesium silicate is dissolved in HCl and the resulting MgCl2 solution is subsequently reacted with CO2 in NH3. HCl and NH3 are recovered from NH4Cl in a two‐step thermal decomposition. Carbonation is investigated from 30 °C to 180 °C at 4 MPa CO2 pressure and Mg‐carbonate morphology transformations with increasing temperature are identified. Nesquehonite (MgCO3 · 3H2O) is obtained below 70 °C, hydromagnesite (Mg5(CO3)4(OH)2 · 4H2O) is formed at 100 °C, and further temperature increase to 180 °C leads to magnesite (MgCO3) precipitation. Nesquehonite and magnesite can fix more CO2 per mole Mg than hydromagnesite.
Designer Ionic Liquid Crystals Based on Congruently Shaped Guanidinium Sulfonates
Authors: Butschies Martin , Frey Wolfgang , Laschat Sabine 
Published: February 2012

AbstractIonic liquid crystals are mesogenic compounds that consist of cations and anions, usually rod‐like cations and spherical anions. Herein we report a new method for the synthesis of ionic liquid crystals by using cations and anions of the same molecular shape with oppositely charged head groups. Thus, 4‐alkoxyphenylpentamethylguanidinium 4‐alkoxyphenylsulfonate ion pairs have been synthesised. 4‐Alkoxyphenylpentamethylguanidinium iodides were also prepared to determine the influence of congruently shaped anions, in comparison with their spherical counterparts, on mesophase behaviour, which was investigated by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X‐ray diffraction (XRD). All the liquid crystalline salts exhibit smectic A mesophases with strongly interdigitated bilayer structures. The guanidinium sulfonate ion pairs show mesomorphic properties from shorter alkyl chain lengths (≥C9) and lower melting points (≈10 K), whereas the corresponding guanidinium iodides are liquid crystalline for longer alkyl chain lengths (≥C14). For chains with ≥C18, however, the mesophase range decreases for the sulfonate ion pairs, but not for the iodide salts.
ansa‐Rare‐Earth‐Metal Catalysts for Rapid and Stereoselective Polymerization of Renewable Methylene Methylbutyrolactones
Authors: Hu Yangjian , Miyake Garret M. , Wang Baoli , Cui Dongmei , Chen Eugene Y.‐X. 
Published: February 2012

AbstractTwo ansa‐half‐sandwich rare‐earth‐metal (REM) dialkyl complexes supported by an ethylene‐bridged fluorenyl (Flu)‐N‐heterocyclic carbene (NHC) ligand, [M{C2H4(η5‐Flu‐κ1‐NHC)}(CH2SiMe3)2] (M=Y, 1; Lu, 2), and a chiral ansa‐sandwich samarocene incorporating a C2 ligand, [Sm(η5‐C12H8)2(thf)2] (3), have been investigated for the coordination–addition polymerization of renewable methylene butyrolactones, α‐methylene‐γ‐butyrolactone (MBL) and γ‐methyl‐α‐methylene‐γ‐butyrolactone (γMMBL). Both ansa‐half‐sandwich complexes 1 and 2 exhibit exceptional activity for the polymerization of γMMBL at room temperature in dimethylformamide (DMF); with a 0.25 mol % catalyst loading, quantitative monomer conversion can be achieved under 1 min, giving a high turn‐over frequency (TOF) of 24 000 h−1. This TOF value represents a rate enhancement, by a factor of 8, 22, or 2400, over the polymerizations by unbridged samarocene [Sm(Cp*)2(thf)2] (Cp*=η5‐pentamethylcyclopentadienyl), by bridged ansa‐samarocene 3 with C2 ligation, or by the corresponding REM trialkyls without the ansa‐Flu‐NHC ligation, respectively. Complexes 1 and 2 are also highly active for the polymerization of β‐methyl‐α‐methylene‐γ‐butyrolactone (βMMBL), realizing the first example of the metal‐mediated coordination polymerization of this monomer and its copolymerization with γMMBL. More remarkably, the resulting PβMMBL homopolymer is highly stereoregular (91 % mm) and exhibits a high Tg of 290 °C. In sharp contrast, catalysts 1 and 2 have poor activity and efficiency in the polymerization of the parent MBL or the acyclic analog methyl methacrylate. Polymerization and kinetic studies using the most active catalyst (1) of the series have uncovered characteristics of its γMMBL polymerization and yielded a unimolecular propagation mechanism. A surprising chain‐initiation pathway for the polymerization in DMF by 1 has been revealed, and catalytic polymerization in the presence of an organoacid has also been examined.
Synthesis of Polycyclic Aromatic Hydrocarbon‐Based Nanovehicles Equipped with Triptycene Wheels
Authors: Jacquot de Rouville Henri‐Pierre , Garbage Romain , Cook Rita E. , Pujol Adeline R. , Sirven Agnès M. , Rapenne Gwénaël 
Published: February 2012

AbstractTwo new nanovehicles that have extended aromatic platforms as the cargo zones have been obtained. Two strategies were considered for the formation of the perylene core from two naphthalene precursors. The first was based on a Scholl‐type reaction involving an oxidant, and the second used a brominated derivative to perform a homocoupling reaction. The first strategy failed under diverse coupling conditions in the presence of several strong oxidants. Nevertheless, the use of CoF3 in trifluoroacetic acid triggered a dimerization reaction between two ester groups of one molecule and the naphthalene unit of another, thereby surprisingly yielding a ten‐membered carbon macrocycle. The second strategy encountered a lack of reactivity of the substrate under several homocoupling conditions. The dimerization was not easily performed but Ullmann‐type conditions ultimately gave the expected product. The low yield and low solubility of the product encouraged us to modify our initial design. The synthesis of a new chassis that incorporated additional tert‐butyl groups improved the solubility of the molecules and also prevented overcyclization of the aromatic platform by blocking these positions. Some p‐phenylene spacers were also intercalated between the iodine and perylene centers to increase the reactivity of the halide towards coupling reactions. Two new chassis were obtained by Scholl‐type oxidative coupling using FeCl3 as the oxidant. The introduction of four triptycene wheels allowed the formation of the two corresponding nanovehicles.