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Thermal Stability (thermal + stability)
Kinds of Thermal Stability Terms modified by Thermal Stability Selected AbstractsCLONING AND SEQUENCING OF THE ,-AMYLASE GENE FROM BACILLUS SUBTILIS US116 STRAIN ENCODING AN ENZYME CLOSELY IDENTICAL TO THAT FROM BACILLUS AMYLOLIQUEFACIENS BUT DISTINCT IN THERMAL STABILITYJOURNAL OF FOOD BIOCHEMISTRY, Issue 2 2010EZZEDINE BEN MESSAOUD ABSTRACT The gene encoding for the ,-amylase AMYUS116 was cloned and sequenced. The amino acid sequence of AMYUS116 exhibited an almost perfect homology with the ,-amylase BACAAM, excluding the residues N205 and N217 of AMYUS116 that were changed to H205 and I217 into BACAAM. Three mutant derivatives from AMYUS116 (N205H, N217I and N205H/N217I) were created by site-directed mutagenesis and their physicochemical and kinetic properties were compared with those of the wild-type enzymes. Therefore, the undertaken amylases mainly generated maltohexaose from starch and had radically the same kinetic parameters and optimum pH and temperature. They, however, were significantly distinct in thermal stability; AMYUS116 was more thermosensible as its half-life time at 80C was 13 min, while those of BACAAM and the double mutant were likewise 38 min. The single-mutant amylases exhibited an identically intermediate thermal stability as their half-life times at 80C were roughly 22 min. PRACTICAL APPLICATIONS Of particular interest to the current search is that the different thermal stability between AMYUS116 and BACAAM can lead to novel findings pertaining to protein stability, which can bring about new strategies for protein engineering. Basically, the comparative study of closely related amylases and the protein engineering of already existing ones are certainly important because they offer opportunities to understand the structure,function relationships of these biocatalysts. [source] One-Dimensional CdII Coordination Polymers: Solid Solutions with NiII, Thermal Stabilities and StructuresEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2004Dejana Vujovic Abstract Reactions of Cd(NCS)2 with 2-, 3- and 4-aminobenzonitrile ligands (2ABN, 3ABN and 4ABN respectively) have produced one-dimensional chain polymers of the general formula [M(NCS)2(ABN)2]n with the metal centres linked by double NCS, bridges. The three cadmium polymers [Cd(NCS)2(3ABN)2]n (1), [Cd(NCS)2(2ABN)2]n (2) and [Cd(NCS)2(4ABN)2]n (3) all differ in their hydrogen-bonding patterns. In terms of ABN coordination, both 1 and 2 exhibit terminal amine coordination while in 3 the ABNs are coordinated through the cyano groups. Crystalline solid solutions of 1 of general formula [Cd1,xNix(NCS)2(3ABN)2]n, containing nickel and cadmium in varying proportions, have also been prepared in order to establish the influence of the metal ratio on the thermal stability and bonding parameters of the polymers. The coordination polymers are not good candidates for forming clathrates while their thermal stability (ranging between 147 and 244 °C) depends on the position of functional groups on the ABN ligands and on the Cd:Ni ratio in the solid solutions. The new polymers have been characterised by single crystal X-ray diffraction, X-ray powder diffraction, electron microscopy, infrared spectroscopy, thermogravimetry and differential scanning calorimetry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis, Crystal Structures and Thermal Stabilities of [Cu(bpp)2(bpdc)(H2O)2]n·2nH2O and [Cu(bpp)2]n·n (tdc) ·7.5nH2OCHINESE JOURNAL OF CHEMISTRY, Issue 10 2008Jing-Hua YU Abstract Two novel copper(II) coordination polymers [Cu(bpp)2(bpdc)(H2O)2]n·2nH2O (1) and [Cu(bpp)2]n·n(tdc)·7.5nH2O (2) (H2bpdc=biphenyl-4,4,-dicarboxylic acid, bpp=1,3-di(4-pyridyl)propane and H2tdc=thiophene-2,5-dicartboxylic acid) have been synthesized by the reactions of Cu(NO3)2 and bpp with the H2bpdc or H2tdc, respectively at room temperature. In the complexes 1 and 2, their Cu atoms have a distorted octahedral geometry, and two water molecules coordinate weakly to the Cu atom in the long axial direction. Both complexes have one-dimensional linear polymer structures. In complex 1, both carboxylate groups of the bpdc can coordinate to Cu atom, while both carboxylate groups of the tdc dianion in complex 2 do not coordinate to the Cu atom, which only balance the charge. In the both complexes, the bpp ligand has different conformation: trans - trans in complex 1 and trans - gauche in complex 2. The thermal gravimetric analyses indicate that both complexes are stable under 110 and 160 °C, respectively. [source] Solvothermal Synthesis, Crystal Structure, and Thermal Stability of Three-Layered Thioantimonate(III) Complexes: [Ni(C3H10N2)3]Sb4S7, [C4H14N2]Sb8S13·H2O, and [C6H18N2]Sb10S16·H2OEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2007Meng Zhang Abstract Three new thioantimonate(III) complexes [Ni(1,2-PDA)3]Sb4S7 (1) (1,2-PDA = 1,2-propanediamine), [dmenH22+]Sb8S13·H2O (2) (dmen = N,N -dimethylethylenediamine), and [deenH22+]Sb10S16·H2O (3) (deen = N,N -diethylethylenediamine), prepared under solvothermal conditions, have been characterized by single-crystal X-ray diffraction, elemental analysis, and DTA-TG measurements. In compound 1, a rectangle-like Sb16S16 heteroring whose dimensions are about 8.1,×,14.7 Å is observed, this is the largest reported pore in layered thioantimonates to date. Further condensation of the Sb16S16 heterorings resulted in an unprecedented framework of the five-atom thick SbxSyn, layer. In 2, a new member of SbnSn (n = 2, 3, 4, 8, 16, 30, 31, 32) heterocycles Sb15S15 heteroring has been obtained as the first example. In compound 3, the most particular feature is that when the secondary Sb,S bonds are considered the Sb2 atom becomes sevenfold coordinated.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Thermal Stability of W- xRe/TiC/SiC Systems,=,0, 5 and 25 at % Re) at High Temperature,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Jerome Roger To ensure the integrity and sustainability of high-temperature applications, the development of protective materials is actually one of the major challenge in materials science. In our study, we examined the effect of a TiC film interlayered between W- xRe (x,=,0, 5 or 25 at % Re) and SiC. The protection given by TiC layer was considered in the 1573,1873,K temperature range and for TiC thicknesses up to about 100,,m. [source] Enhanced Thermal Stability and Efficiency of Polymer Bulk-Heterojunction Solar Cells by Low-Temperature Drying of the Active LayerADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Ching Lin Abstract This study addresses two key issues, stability and efficiency, of polymer solar cells based on blended poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) by demonstrating a film-forming process that involves low-temperature drying (,5,°C) and subsequent annealing of the active layer. The low-temperature process achieves 4.70% power conversion efficiency (PCE) and ,1250,h storage half-life at 65,°C, which are significant improvements over the 3.39% PCE and ,143,h half-life of the regular room-temperature process. The improvements are attributed to the enhanced nucleation of P3HT crystallites as well as the minimized separation of the P3HT and PCBM phases at the low drying temperature, which upon post-drying annealing results in a morphology consisting of small PCBM-rich domains interspersed within a densely interconnected P3HT crystal network. This morphology provides ample bulk-heterojunction area for charge generation while allowing for facile charge transport; moreover, the P3HT crystal network serves as an immobile frame at heating temperatures less than the melting point (Tm) of P3HT, thus preventing PCBM/P3HT phase separation and the corresponding device degradation. [source] Preparation of Oriented Aluminum Nitride Thin Films on Polyimide Films and Piezoelectric Response with High Thermal Stability and FlexibilityADVANCED FUNCTIONAL MATERIALS, Issue 3 2007M. Akiyama Abstract c -Axis oriented aluminum nitride (AlN) thin films are successfully prepared on amorphous polyimide films by radiofrequency magnetron reactive sputtering at room temperature. Structural analysis shows that the AlN films have a wurtzite structure and consist of c -axis oriented columnar grains about 100,nm wide. The full width at half maximum of the X-ray diffraction rocking curves and piezoelectric coefficient d33 of the AlN films are 8.3° and 0.56,pC,N,1, respectively. The AlN films exhibit a piezoelectric response over a wide temperature range, from ,196 to 300,°C, and can measure pressure within a wide range, from pulse waves of hundreds of pascals to 40,MPa. Moreover, the sensitivity of the AlN films increases with the number of times it was folded, suggesting that we can control the sensitivity of the AlN films by changing the geometric form. These results were achieved by a combination of preparing the oriented AlN thin films on polyimide films, and sandwiching the AlN and polymer films between top and bottom electrodes, such as Pt/AlN/polyimide/Pt. They are thin (less than 10,,m), self powered, adaptable to complex contours, and available in a variety of configurations. Although AlN is a piezoelectric ceramic, the AlN films are flexible and excellent in mechanical shock resistance. [source] Highly Efficient Non-Doped Blue Organic Light-Emitting Diodes Based on Fluorene Derivatives with High Thermal Stability,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2005L. Tao Abstract A new series of blue-light-emitting fluorene derivatives have been synthesized and characterized. The fluorene derivatives have high fluorescence yields, good thermal stability, and high glass-transition temperatures in the range 145,193,°C. Organic light-emitting diodes (OLEDs) fabricated using the fluorene derivatives as the host emitter show high efficiency (up to 5.3,cd,A,1 and 3.0,lm,W,1) and bright blue-light emission (Commission Internationale de L'Eclairage (CIE) coordinates of x,=,0.16, y,=,0.22). The performance of the non-doped fluorene-based devices is among the best fluorescent blue-light-emitting OLEDs. The good performance of the present blue OLEDs is considered to derive from: 1),appropriate energy levels of the fluorene derivatives for good carrier injection; 2),good carrier-transporting properties; and 3),high fluorescence efficiency of the fluorene derivatives. These merits are discussed in terms of the molecular structures. [source] Single-Crystalline Gallium Nitride Microspindles: Synthesis, Characterization, and Thermal Stability ,ADVANCED FUNCTIONAL MATERIALS, Issue 5 2004F. Xu Abstract This paper describes a facile procedure for synthesizing high-quality gallium nitride microspindles on a large scale using a solid-state reaction of GaI3, NaNH2, and NH4Cl in a sealed system at 500,°C for 6,h. The structures, compositions, and morphologies of the as-synthesized products are derived from X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FE-SEM). The selected-area electron diffraction (SAED) patterns and high-resolution transmission electron microscopy (HRTEM) images show that the as-synthesized GaN spindles are composed of many single-crystalline platelets. The GaN microspindles show different optical properties depending on their shape (e.g., nanowires or nanoparticles) in photoluminescence (PL) emission spectroscopy and Raman spectroscopy. The possible growth mechanism of GaN microspindles is controlled by linear kinetics with a driving force proportional to the difference between a local supersaturation and an equilibrium chemical potential. Furthermore, the thermal stability of the GaN microspindles is investigated under various annealing conditions and discussed on the basis of additional TEM and XRD analyses. [source] Bismuth,Ceramic Nanocomposites with Unusual Thermal Stability via High-Energy Ball Milling,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2003M.A. Meitl Abstract Electrically conducting nanocomposites of bismuth metal and insulating ceramic phases of SiO2 and MgO were generated via high-energy ball milling for 24 h using zirconia milling media. The resulting nanocomposites contain Bi nanoparticles with sizes down to 5 nm in diameter. The morphology is a strong function of the oxide phase: specifically, the Bi appears to wet MgO while it forms spherical nanoparticles on the SiO2. X-ray diffraction measurements indicate a nominal bismuth grain size of 50 nm, and peak fitting to a simple bidisperse model yields a mixture of approximately 57,% bulk bismuth and 43,% 27 nm diameter crystallites. Nanoparticles as small as 5 nm are observed in transmission electron microscopy (TEM), but may not constitute a significant volume fraction of the sample. Differential scanning calorimetry reveals dramatic broadening in the temperatures over which melting and freezing occur and a surprising persistence of nanostructure after thermal cycling above the melting point of the Bi phase. [source] Supramolecular Self-Assembled Dendritic Nonlinear Optical Chromophores: Fine-Tuning of Arene,Perfluoroarene Interactions for Ultralarge Electro-Optic Activity and Enhanced Thermal StabilityADVANCED MATERIALS, Issue 19 2009Xing-Hua Zhou Unprecedented electro-optic (EO) activity and excellent alignment stability at 85,°C are demonstrated through rational design of a new series of dendronized polyenic chromophores capable of supramolecular self-assembly directed by fine-tuned arene,perfluoroarene interactions. Analysis of the EO properties showed exceptional poling efficiency for these molecular glasses at high chromophore number density. [source] Synthesis and Assembly of Monodisperse High-Coercivity Silica-Capped FePt Nanomagnets of Tunable Size, Composition, and Thermal Stability from Microemulsions,ADVANCED MATERIALS, Issue 19 2006Q. Yan A microemulsion approach to obtain high - coercivity (850 mT) FePt nanomagnets capped with a nanoscopic silica shell is reported (see figure). This versatile method allows the easy tuning of particle size and composition. The silica shell inhibits agglomeration and preserves the chemical stability of the particles up to 650,°C, and facilitates surface functionalization and particle assembly. These attributes are attractive for harnessing the nanomagnets for realizing novel devices and composites. [source] Effects of Inulin/Oligofructose on the Thermal Stability and Acid-Induced Gelation of Soy ProteinsJOURNAL OF FOOD SCIENCE, Issue 2 2008Y.-C. Tseng ABSTRACT:, Differential scanning calorimetry (DSC) and dynamic oscillatory shear testing were performed to study the influence of inulin (Raftiline® HP-gel and Raftiline® ST-gel) and oligofructose (Raftilose® P95) on the thermal stability and gelation (using glucono-,-lactone [GDL] as a coagulant) of soy protein isolate (SPI) dispersions. Addition of 10% (w/v) inulin/oligofructose or sucrose increased (P < 0.05) the peak denaturation temperatures (Tm) of 7S and 11S soy proteins in SPI dispersion (5%[w/v], pH 7.0) by an average of 1.9 and 2.3 °C, respectively. GDL induced SPI thermal gelation, and the gel rheology was affected by both the pH decline and the specific temperature of heating. Addition of inulin/oligofructose (8%, w/v) improved the gelling properties of preheated SPI dispersion (8%, w/v) coagulated with GDL, showing 14.4 to 45.6% increase (P < 0.05) in gel rigidity (G, value) at the end of heating (81 °C). Microstructural examination revealed a denser protein cross-linking structure and reduced pore sizes in SPI gels containing inulin/oligofructose. In general, inulin was more capable of improving SPI gelation than oligofructose, suggesting that the degree of fructose polymerization in the fructans was of thermal and rheological importance. [source] Thermal Stability of (1,x)BiScO3,xPbTiO3 Piezoelectric Ceramics for High-Temperature Sensor ApplicationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Si Chen High-temperature piezoelectric (1,x)BiScO3,xPbTiO3 ceramics with composition (x=0.62, 0.63, 0.64, and 0.65) near the morphotropic phase boundary were fabricated. A thermal depoling experiment was used to investigate the stability of polarization at the temperature range from 200° to 460°C. The results indicated that samples with rhombohedral phase began to depole when the temperature was higher than 300°C, while samples with a tetragonal phase showed good resistance to thermal depoling up to 440°C, close to their Curie temperature. [source] Effect of B2O3 Addition on the Thermal Stability of Barium Phosphate Glasses for Optical Fiber DevicesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2004Takashi Harada The effect of B2O3 addition on the thermal stability of BaO,P2O5 glasses is studied by differential thermal analysis (DTA), X-ray diffraction (XRD) analysis, scanning electron microscopy, and micro-Raman spectroscopy. The difference between glass-transition and onset-crystallization temperatures increases monotonically with increasing B2O3 concentration. The DTA result reveals that no exothermic peak due to surface crystallization exists in the BaO,P2O5 glass doped with 3 mol% B2O3. A single-mode BaO,P2O5 -B2O3 glass fiber could be fabricated by a rod-in-tube technique. The modification of glass structure due to B2O3 addition is qualitatively discussed. [source] Thermal Stability of a Chemically Vapor Deposited Multilayer Coating Containing Amorphous Silica and Rutile Titania on Hi-Nicalon FiberJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003Jinil Lee A multilayer coating consisting of consecutive layers of amorphous-silica, rutile-titania, and amorphous-silica was prepared on Hi-Nicalon fiber by chemical vapor deposition at 1050°C. It appeared that the silica and titania layers were strongly bonded to each other with no evidence of detachment and crack deflection at the interface region. The layered structure became morphologically unstable because of the growth of titania grains, the crystallization of the silica layers, and the oxidation of the fiber on exposure to 1200°C in air for 92 h. [source] Thermal Stability of Lanthanum Zirconate Plasma-Sprayed CoatingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001X. Q. Cao Lanthanum zirconate (La2Zr2O7, LZ) is a newly proposed material for thermal barrier coatings (TBCs). The thermal stability of LZ coating was studied in this work by long-term annealing and thermal cycling. After long-term annealing at 1400°C or thermal cycling, both LZ powder and plasma-sprayed coating still kept the pyrochlore structure, and a preferred crystal growth direction in the coating was observed by X-ray diffraction. A considerable amount of La2O3 in the powder was evaporated in the plasma flame, resulting in a nonstoichiometric coating. Additionally, compared with the standard TBC material yttria-stabilized zirconia (YSZ), LZ coating has a lower thermal expansion coefficient, which leads to higher stress levels in a TBC system. [source] Spectroscopic Properties and Thermal Stability of Er3+ -Doped Germanotellurite Glasses for Broadband Fiber AmplifiersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2001Xian Feng The thermal stability and spectroscopic properties of Er2O3 -doped TeO2,GeO2,ZnO,Na2O,Y2O3 glasses for 1.5 ,m fiber amplifiers were investigated. The thermal stability of the 75TeO2·20ZnO· 5Na2O glass was improved by introducing GeO2 and Y2O3. The radiative transition and the nonradiative transition have a dominant influence on the 4I13/2 level lifetime of Er3+ in high- and low-GeO2 regions, respectively. Adding Y2O3 increases the 4I13/2 level lifetime of Er3+ significantly. The Judd,Ofelt (J-O) parameter ,6 shows a strong correlation with the 1.5 ,m emission bandwidth; and the larger the ,6, the wider the bandwidth. [source] Investigation of the Decomposition Mechanism and Thermal Stability of Nitrocellulose/Nitroglycerine Based Propellants by Electron Spin ResonancePROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 2 2007Anton Chin Abstract Nitrocellulose based (NC) and nitroglycerin based (NG) propellants often have a fixed acid and water content during the manufacturing time. After manufacture, the quantity and ratio of acid/water will continue to vary depending upon the conditions of storage and operation. The level of variation depends on many factors such as loading density, temperature, volume of ullage and sealing condition of the containing cartridge, just to name a few. As described in this paper and other literature, the degradation mechanisms and aging processes of NC/NG based propellants are extremely complicated. This paper describes the details of the application of Electron Spin Resonance (ESR) to study if the free-radical mechanism is involved in the decomposition of nitrocellulose and nitroglycerin. Due to the high free-radical intensity possessed by the propellant composition, we believe that a , complex intermediate may be formed between DPA and NG and/or NC. The formation of a , complex intermediate is not preferred because it may enhance the rate of decomposition of nitrate esters. [source] Triazolate Counter Ions in AuI Complexes: Catalysts with Improved Thermal StabilityCHEMCATCHEM, Issue 2 2010Stephen Counter revolution: Most homogeneous gold-catalyzed transformations employ gold(I) complexes with weakly coordinating anions, which, their remarkable activity notwithstanding, lack stability at higher temperatures. Shi et,al. have described the synthesis of simple phosphine-based gold(I) complexes with triazolates as counter ions. The compounds are highly thermostable and good catalysts for intermolecular hydroaminations. [source] Approaches to Open Fullerenes: Synthesis and Thermal Stability of cis-1 Bis(isobenzofuran) Diels,Alder Adducts of C60.CHEMINFORM, Issue 26 2007Michael Sander Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Crystal Structures of KNdTe4, RbPrTe4, and RbNdTe4 , Investigations Concerning the Thermal Stability of KNdTe4 as well as Some Remarks Concerning Additional Representatives of the Composition ALnTe4 (A: K, Rb, Cs and Ln: Rare Earth Metal).CHEMINFORM, Issue 20 2003Klaus Stoewe Abstract For Abstract see ChemInform Abstract in Full Text. [source] Cycling and Thermal Stability of Nanostructured MgH2,Cr2O3 Composite for Hydrogen Storage.CHEMINFORM, Issue 7 2003Z. Dehouche Abstract For Abstract see ChemInform Abstract in Full Text. [source] Thermal Stability of Dehydrophenylalanine-Containing Model Peptides as Probed by Infrared Spectroscopy: a Case Study of an , -Helical and a 310 -Helical PeptideCHEMISTRY & BIODIVERSITY, Issue 3 2006Alka Gupta Abstract The temperature-dependent secondary-structural changes in the two known helical model peptides Boc-Val-,Phe-Ala-Leu-Gly-OMe (1; , -helical) and Boc-Leu-Phe-Ala-,Phe-Leu-OMe (2; 310 -helical), which both comprise a single dehydrophenylalanine (,Phe) residue, were investigated by means of FT-IR spectroscopy (peptide film on KBr). Both the first-order and the better-resolved second-order derivative IR spectra of 1 and 2 were analyzed. The ,(NH) (3240,3340,cm,1), the Amide-I (1600,1700,cm,1), and the Amide-II (1510,1580,cm,1) regions of 1 and 2 showed significant differences in thermal-denaturation experiments (22°,144°), with the 310 -helical peptide (2) being considerably more stable. This observation was rationalized by different patterns and strengths of intramolecular H-bonds, and was qualitatively related to the different geometries of the peptides. Also, a fair degree of residual secondary-structural elements were found even in the ,denatured' states above 104° (1) or 134° (2). [source] Crystal Structure, Thermal Stability and Luminescence of Coordination Polymer [Cd(BBP)(p -PDOA)]nCHINESE JOURNAL OF CHEMISTRY, Issue 8 2007Yan Yang Abstract Hydrothermal reaction of Cd(NO3)2·4H2O with bbp and p -PDOAH2 at 140 °C yielded a novel 1D cadmium(II) coordination polymer, [Cd(bbp)(p -PDOA)]n (bbp2,6-bis(benzimidazol-2-yl)pyridine, p -PDOAp -phenylenedioxy- diacetate dianion), in which CdN3O4 pentagonal bipyramids were linked by p -PDOA ligands in a bis-bidentate mode to construct a zigzag chain with the adjacent Cd···Cd distance of 1.14(1) nm. There exists a 2D supramolecular network linked by ,-, stacking with a face-to-face distance of 0.35(1) nm between the 2,6-bis(benzimidazol-2-yl) pyridine ligands and hydrogen-bonding interactions (0.27(4) nm). A 3D supramolecular network was further constructed by these non-covalent interactions between the zippers. The TG/DTG showed that its chain skeleton was thermally stable up to 389 °C and the blue fluorescent emission of the complex was determined at 428 nm in a solid state with its long decay lifetime of 7.24 ns. [source] Synthesis and characterization of phthalazinone containing poly(arylene ether)s via a novel N,C coupling reactionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2003S. J. Wang Abstract High-molecular-weight poly(phthalazinone)s with very high glass-transition temperatures (Tg's) were synthesized via a novel N,C coupling reaction. New bisphthalazinone monomers (7a,e) were synthesized from 2-(4-chlorobenzoyl) phthalic acid in two steps. Poly(phthalazinone)s, having inherent viscosities in the range of 0.34,0.91 dL/g, were prepared by the reaction of the bis(phthalazinone) monomers with an activated aryl halide in a dipolar aprotic solvent in the presence of potassium carbonate. The poly(phthalazinone)s exhibited Tg's greater than 230 °C. polymer 8b synthesized from diphenyl biphenol and bis(4-flurophenyl) sulfone demonstrated the highest Tg of 297 °C. Thermal stabilities of the poly(phthalazinone)s were determined by thermogravimetric analysis. All the poly(phthalazinone)s showed a similar pattern of decomposition with no weight loss below 450 °C in nitrogen. The temperatures of 5% weight loss were observed to be about 500 °C. The poly(phthalazinone)s containing 4,4,-isopropylidenediphenol and 4,4,-(hexafluoroisopropylidene) diphenol and diphenyl ether linkage were soluble in chlorinated solvents such as chloroform. Other poly-(phthalazinone)s were soluble in dipolar aprotic solvents such as N,N,-dimethylacetamide. The soluble poly(phthalazinone)s can be cast as flexible films from solution. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2481,2490, 2003 [source] Structure and properties of multi-walled carbon nanotubes/polyethylene nanocomposites synthesized by in situ polymerization with supported Cp2ZrCl2 catalystPOLYMER COMPOSITES, Issue 3 2010Shiyun Li Multi-walled carbon nanotubes (MWCNTs)/polyethylene (PE) nanocomposites were prepared via in situ polymerization with MWCNTs supported Bis- (cyclopentadienyl) zirconium dichloride (Cp2ZrCl2) catalyst. X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscope (FESEM) results implied that Cp2ZrCl2 catalyst was immobilized in the surface of the MWCNTs supports via a bridge of methylaluminoxane (MAO). The efficient dispersion of MWCNTs in PE matrix and the strong compressive forces associated with PE on the MWCNTs were demonstrated by means of transmission electron microscope (TEM), FESEM and Raman spectra. With introducing 0.2 wt% MWCNTs, both the tensile strength and elongation of MWCNTs/PE nanocomposite were improved by factors of 1.6 (from 29 to 45 MPa) and 1.5 (from 909% to 1360%) comparing with the pure PE, respectively. Morphology observation of fractured surface revealed that the PE firmly adhered to the nanotubes, which was responsible for the significant improvement of the mechanical properties of nanocomposites. Thermal stabilities of the nanocomposites were significantly improved. In addition, the MWCNTs/PE nanocomposites showed very high ultraviolet (UV) shielding property, which could increase photooxidative stability of the PE. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source] A Series of Novel Organically Templated Germanium Antimony SulfidesCHEMISTRY - AN ASIAN JOURNAL, Issue 8 2010Mei-Ling Feng Dr. Abstract A series of novel organically templated germanium antimony sulfides have been solvothermally synthesized and structurally, thermally, and optically characterized. The compound [Me2NH2]6[(Ge2Sb2S7)(Ge4S10)] (1) features two distinct tetranuclear [Ge2Sb2S7]2, and [Ge4S10]4, isolated clusters. The compound [(Me)2NH2][DabcoH]2[Ge2Sb3S10] (2) (Dabco=triethylenediamine) features a 1D-[Ge2Sb3S10]n3n, ribbon constructed with two [GeSbS5]n3n, chains bridged by Sb3+ ion in , -SbS4 configuration. Compounds [M(en)3][GeSb2S6] (M=Ni (3), Co (4) en=ethylenediamine) feature the unique 2D grid layer structures of [GeSb2S6]n2n,. The compound [(Me)2NH2]2[GeSb2S6] (5) previously reported by us features a 3D chiral microporous structure with the chiral channels. The optical absorption spectra indicate that all the compounds are wide bandgap semiconductors. Thermal stabilities of these compounds have been investigated by thermogravimetric analyses (TGA). [source] Directed evolution of formate dehydrogenase from Candida boidinii for improved stability during entrapment in polyacrylamideFEBS JOURNAL, Issue 17 2006Marion B. Ansorge-Schumacher In two cycles of an error-prone PCR process, variants of formate dehydrogenase from Candida boidinii were created which revealed an up to 4.4-fold (440%) higher residual activity after entrapment in polyacrylamide gels than the wild-type enzyme. These were identified in an assay using single precursor molecules of polyacrylamide instead of the complete gel for selection. The stabilization resulted from an exchange of distinct lysine, glutamic acid, and cysteine residues remote from the active site, which did not affect the kinetics of the catalyzed reaction. Thermal stability increased at the exchange of lysine and glutamic acid, but decreased due the exchange of cysteine. Overall, the variants reveal very suitable properties for application in a technical synthetic process, enabling use of entrapment in polyacrylamide as an economic and versatile immobilization method. [source] A theoretical investigation on the structures, densities, detonation properties, and pyrolysis mechanism of the nitro derivatives of phenolsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2010Guixiang Wang Abstract The nitro derivatives of phenols are optimized to obtain their molecular geometries and electronic structures at the DFT-B3LYP/6-31G* level. Detonation properties are evaluated using the modified Kamlet,Jacobs equations based on the calculated densities and heats of formation. It is found that there are good linear relationships between density, detonation velocity, detonation pressure, and the number of nitro and hydroxy groups. Thermal stability and pyrolysis mechanism of the title compounds are investigated by calculating the bond dissociation energies (BDEs) at the unrestricted B3LYP/6-31G* level. The activation energies of H-transfer reaction is smaller than the BDEs of all bonds and this illustrates that the pyrolysis of the title compounds may be started from breaking OH bond followed by the isomerization reaction of H transfer. Moreover, the CNO2 bond with the smaller bond overlap population and the smaller BDE will also overlap may be before homolysis. According to the quantitative standard of energetics and stability as a high-energy density compound, pentanitrophenol essentially satisfies this requirement. In addition, we have discussed the effect of the nitro and hydroxy groups on the static electronic structural parameters and the kinetic parameter. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] | |||||||||||||||||||||||||||||||||||||