排序方式: 共有104条查询结果,搜索用时 687 毫秒
91.
Mireia Morell Albena Lederer Xavier Ramis Brigitte Voit Angels Serra 《Journal of polymer science. Part A, Polymer chemistry》2011,49(11):2395-2406
Well‐defined multiarm star copolymers, hyperbranched poly(glycidol)‐b‐poly(ε‐caprolactone), with an average of 100–110 arms per molecule and a molecular weight of arms of 3000 g/mol (PGOH‐b‐PCL30) and 1000 g/mol (PGOH‐b‐PCL10) were synthesized by cationic ring‐opening polymerization of ε‐caprolactone from a poly(glycidol) core and used to modify diglycidylether of bisphenol A formulations. The curing process, studied by dynamic scanning calorimetry, was only slightly retarded when PGOH‐b‐PCLx were added to the formulation. By rheometry, the effect of this new topology and the arm length on the complex viscosity (η*) and gelation of the reactive mixture was analyzed in detail. The addition of these new reactive modifiers decreases the global shrinkage and increases the conversion at gelation. In addition, the modified thermosets have an improved reworkability. The homogeneity of pure DGEBA and modified thermosets was proved by dynamic thermomechanical analysis and electronic microscopy (FESEM). Addition of star‐like structures led to a more toughened fracture of the thermoset in comparison to pure DGEBA. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
92.
Mireia Morell David Foix Albena Lederer Xavier Ramis Brigitte Voit Àngels Serra 《Journal of polymer science. Part A, Polymer chemistry》2011,49(21):4639-4649
A well‐defined multiarm star copolymer poly(styrene)‐b‐poly(ε‐caprolactone) (PSOH‐b‐PCL) with an average number of PCL arms per molecule of 60 has been prepared. 4‐Chloromethyl styrene (4‐CMS) was polymerized by means of atom transfer radical polymerization (ATRP) to obtain a hyperbranched poly(styrene) with chlorines as terminal groups. Subsequently, chlorines were substituted by reaction with diisopropanolamine (DIPA) to give the hydroxyl‐ended derivative. Finally, the hydroxyl‐ended hyperbranched poly(styrene) has been used as a macroinitiator core to polymerize ε‐caprolactone by means of cationic ring‐opening polymerization so as to obtain the star copolymer. In a second step, PSOH‐b‐PCL was used as reactive modifier of diglycidylether of bisphenol A formulations cured by 1‐methyl imidazole (1‐MI) obtaining nanostructured thermosets. The curing process was studied by dynamic scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). By rheometry, the effect of this new polymer topology on the complex viscosity (η*) of the reactive mixture and on the gelation process was also analyzed. The thermomechanical characteristics of the modified materials were determined. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
93.
Several chemical modifiers based on palladium have been evaluated: the individual Pd(II) and the mixed modifiers Pd + Zr, Pd + W, Pd + Zr + citric acid, Pd + W + citric acid. The mechanisms by which these chemical modifiers stabilize analytes and control atomization have been suggested. Factors that might have an influence on the characteristic mass and non-spectral interferences are discussed. The advantages and limitations of the palladium-tungsten modifiers are shown. 相似文献
94.
A. Bachvarova-Nedelcheva R. Iordanova St. Yordanov Y. Dimitriev 《Journal of Non》2009,355(37-42):2027-2030
The aim of this work is to obtain multicomponent selenite glasses containing other non-traditional glass formers such as V2O5, TeO2 and MoO3 and to verify their optical properties in the visible spectral region. Glasses containing MoO3 and TeO2 are transparent in the visible range and near IR region from 400 to 2300 nm. Transparent coloured glasses were obtained due to the electron transfer charge processes. Using IR spectroscopy it was determined the main building units of the amorphous network. It was found the presence of TeO4, SeO3 and MoO4 units. 相似文献
95.
In order to control the fabrication method, the mechanism used in the formation of DNA templated nanowires is investigated through circular dichroism (CD) spectroscopy. Metallic (Au) and magnetic (Fe2O3 and CoFe2O4) nanoparticles (NP) are aligned along the DNA strand at various mass ratios. The DNA templated nanowires are compared to the structure of B‐form dsDNA through CD experiments. Absorbance and thermal melting tests are performed to verify the structural changes of DNA templated nanowires. Low concentrations of nanoparticles preserve the DNA B‐form through electrostatic interactions. Conversely, at higher concentrations of nanoparticles aligned along the DNA strand, the template is denatured. Information on the mode of nanoparticle binding and DNA helix alterations are explored for metallic and magnetic nanowires based upon the results. 相似文献
96.
Zlatan Denchev Milena Tomanova Albena Lederer 《Journal of polymer science. Part A, Polymer chemistry》2008,46(15):5142-5156
Ethyl‐(ECA) and butyl‐2‐cyanoacrylate (BCA) monomers of high purity and acidic stabilization were synthesized and anionically polymerized to homo‐ and copolymers in two different ways: by piperidine‐catalyzed bulk polymerization leading to transparent, brittle films (method A) and by polymerization in aqueous medium in the presence of sodium bicarbonate to obtain white powders (Method B). The molecular structure of the synthesized monomers, homopolymers and copolymers were corroborated by spectral methods. The polymers were studied further by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), size exclusion chromatography (SEC) and proton nuclear magnetic resonance (1H NMR). Controlling the composition of the monomer feed and the way the polymerization was performed, it was possible to obtain phase separated or homogeneous cyanoacrylate copolymers with glass transitions varying between the Tg of polyECA and that of polyBCA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5142–5156, 2008 相似文献
97.
Boryana G.?KotzevaEmail author Irina D.?Gocheva Nikolay B.?Piperov Ivan P.?Havezov Albena K.?Detcheva 《Mikrochimica acta》2004,147(4):231-236
Two methods of opening fluid inclusions in hydrothermal quartz from Madan (Bulgaria) – mechanical (crushing) and thermal (decrepitation), followed by water leaching of the released components – were applied and compared. Problems concerning the sample preparation procedure, such as choice of an optimal sample mass and grain fraction, contamination of the grain surfaces, as well as the influence of La3+ and Cs+ additions on the water leaches etc., are discussed. The mol ratios X/Na (X=K, Ca, Mg, Mn) were determined by flame or electrothermal vaporization AAS of the dilute solutions obtained. The total salinity of inclusion fluid estimated by classical microcryometry is used to calculate the total concentrations of the main ions (Na+, K+, Ca2+, Mg2+ and Mn2+) in the water phase of the inclusions. Furthermore, the maximum concentrations of Pb2+ and Cu2+ were evaluated. 相似文献
98.
Huang H Wang H Kozekova A Rizzo CJ Stone MP 《Journal of the American Chemical Society》2011,133(40):16101-16110
Michael addition of trans-4-hydroxynonenal (HNE) to deoxyguanosine yields diastereomeric 1,N(2)-dG adducts in DNA. When placed opposite dC in the 5'-CpG-3' sequence, the (6S,8R,11S) diastereomer forms a N(2)-dG:N(2)-dG interstrand cross-link [Wang, H.; Kozekov, I. D.; Harris, T. M.; Rizzo, C. J. J. Am. Chem. Soc.2003, 125, 5687-5700]. We refined its structure in 5'-d(G(1)C(2)T(3)A(4)G(5)C(6)X(7)A(8)G(9)T(10)C(11)C(12))-3'·5'-d(G(13)G(14)A(15)C(16)T(17)C(18)Y(19)C(20)T(21)A(22)G(23)C(24))-3' [X(7) is the dG adjacent to the C6 carbon of the cross-link or the α-carbon of the (6S,8R,11S) 1,N(2)-dG adduct, and Y(19) is the dG adjacent to the C8 carbon of the cross-link or the γ-carbon of the HNE-derived (6S,8R,11S) 1,N(2)-dG adduct; the cross-link is in the 5'-CpG-3' sequence]. Introduction of (13)C at the C8 carbon of the cross-link revealed one (13)C8→H8 correlation, indicating that the cross-link existed predominantly as a carbinolamine linkage. The H8 proton exhibited NOEs to Y(19) H1', C(20) H1', and C(20) H4', orienting it toward the complementary strand, consistent with the (6S,8R,11S) configuration. An NOE was also observed between the HNE H11 proton and Y(19) H1', orienting the former toward the complementary strand. Imine and pyrimidopurinone linkages were excluded by observation of the Y(19)N(2)H and X(7) N1H protons, respectively. A strong H8→H11 NOE and no (3)J((13)C→H) coupling for the (13)C8-O-C11-H11 eliminated the tetrahydrofuran species derived from the (6S,8R,11S) 1,N(2)-dG adduct. The (6S,8R,11S) carbinolamine linkage and the HNE side chain were located in the minor groove. The X(7)N(2) and Y(19)N(2) atoms were in the gauche conformation with respect to the linkage, maintaining Watson-Crick hydrogen bonds at the cross-linked base pairs. A solvated molecular dynamics simulation indicated that the anti conformation of the hydroxyl group with respect to C6 of the tether minimized steric interaction and predicted hydrogen bonds involving O8H with C(20)O(2) of the 5'-neighbor base pair G(5)·C(20) and O11H with C(18)O(2) of X(7)·C(18). These may, in part, explain the stability of this cross-link and the stereochemical preference for the (6S,8R,11S) configuration. 相似文献
99.
Albena K. Detcheva Paunka S. Vassileva Ralitsa H. Georgieva Dimitrinka K. Voykova Tsvetelina I. Gerganova Yordanka Y. Ivanova 《Central European Journal of Chemistry》2011,9(5):932-940
In the present work the adsorption of some transition metal ions from aqueous solutions on a silica-based nanostructured hybrid
material modified by aluminium was investigated. The novel organic-inorganic material was synthesized via a sol-gel method through hydrolysis and co-condensation reactions. Its structure was characterized by means of SEM, XRD and
FTIR. Based on the data obtained the most probable cross-linking mechanism for the derived xerogel was proposed. The characterization
of its texture parameters was carried out by low-temperature adsorption of nitrogen. The adsorption properties of this material
with respect to Cu(II), Cr(III) and Pb(II) ions from single-component aqueous solutions and multi-component aqueous solutions
containing also Cd(II) and Fe(III) were evaluated. The effect of contact time, acidity of initial solutions and metal ion
concentrations was investigated using the batch method. Pseudo-first order, pseudo-second order and intraparticle diffusion
models were used to analyze kinetic data. In all cases the adsorption was significantly affected by the pH value. Equilibrium
modelling data were fitted to linear Langmuir, Freundlich and Dubinin-Radushkevich models. Best fit was observed for Langmuir
model, which showed determination coefficients greater than 0.992 for all ions studied. The maximum adsorption capacities
for single- and multi-component adsorption were calculated.
相似文献
100.
We present a facile, simple method to detect DNA methylation by measuring the transverse proton relaxation behaviour. Positively charged nanoparticles are arranged along the negatively charged backbone of DNA strands through electrostatic interactions. The arrangement of NPs along DNA strands aids to amplify and compare the transverse proton relaxation signal for un-cut versus cut DNA strands cleaved by sequence specific restriction enzymes. Results from this study suggest that the presence of methylation on DNA can be detected using superparamagnetic NPs using NMR. 相似文献