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51.
Marcos L. Dias Luciana P. da Silva Geraldo L. Crossetti Griselda B. Galland Carlos A. L. Filgueiras Cludio M. Ziglio 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):458-466
DADNiX2 nickel–diimine complexes [DAD = 2,6‐iPr2? C6H3? N?C(Me)? C(Me)?N? 2,6‐iPr2? C6H3] containing nonchelating pseudohalide ligands [X = isothiocyanate (NCS) for complex 1 and isoselenocyanate (NCSe) for complex 2 ] were synthesized, and the propylene polymerization with these complexes and also with the Br ligand (X = Br for complex 3 ) activated by methylaluminoxane (MAO) were investigated (systems 1 , 2 , and 3 /MAO). The polypropylenes obtained with systems 1 , 2 , and 3 were amorphous polymers and had high molecular weights and narrow molecular weight distributions. Catalyst system 1 showed a relatively high activity even at a low Al/Ni ratio and reached the maximum activity at the molar ratio of Al/Ni = 500, unlike system 3 . Increases in the reaction temperature and propylene pressure favored an increase in the catalytic activity. The spectra of polypropylenes looked like those of propylene–ethylene copolymers containing syndiotactic propylene and ethylene sequences. At the same temperature and pressure, system 2 presented the highest number of propylene sequences, and system 3 presented the lowest. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 458–466, 2006 相似文献
52.
Fernanda F. Nunes Escher Griselda Barrera Galland Mrcio Ferreira 《Journal of polymer science. Part A, Polymer chemistry》2003,41(16):2531-2541
Many studies have been reported on the 13C NMR characterization of ethylene–α‐olefin copolymers, but only a few have been reported on terpolymers. The incorporation of an α‐olefin into the polyethylene chain changes the structure and, consequently, the properties of the polymer obtained. Looking for new products, we obtained a series of ethylene–propylene–1‐decene terpolymers with the metallocenic system rac‐ethylene bisindenyl zirconium dichloride/methylaluminoxane. We performed a complete 13C NMR characterization of these terpolymers qualitatively and quantitatively. Here we present a detailed study of the 13C NMR chemical shifts, triad sequence distributions, monomer average sequence lengths, and reactivity ratios for these terpolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2531–2541, 2003 相似文献
53.
Marcéo A. Milani Raul Quijada Nara R. S. Basso Ana P. Graebin Griselda B. Galland 《Journal of polymer science. Part A, Polymer chemistry》2012,50(17):3598-3605
In this work, the synthesis of polypropylene (PP)/graphene nanosheet (GNS) nanocomposites by in situ polymerization using metallocene catalysts was studied. Initial reactions were performed using rac‐Et(Ind)2ZrCl2 and rac‐Me2Si(Ind)2ZrCl2 catalysts to select the best one to obtain good molecular weight, thermal properties, and tacticity. Subsequently, PP nanocomposites with different loadings of GNS were obtained. GNS from two different sources [Graphite Nacional (GN) and Graphite Aldrich (GA)] have been used, and the differences between the obtained nanocomposites were evaluated. The GNS and nanocomposites were studied by scanning electronic microcopy, transmission electronic microcopy, and X‐ray diffraction. They showed that the GN nanosheets had lower crystal size and diameter than the GA nanosheets and dispersed better in the PP matrix. Differential scanning calorimetry analyses of both types of nanocomposites showed an increase in the crystallization temperature with increasing graphite loading. The polymeric materials were also characterized by GPC, thermogravimetric analysis, and 13C NMR. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
54.
Dr. J. Reyes Flores Dr. Griselda Castruita-De León Dr. Gleb Turlakov Dr. Eduardo Arias Dr. Ivana Moggio Dr. Sagrario M. Montemayor Dr. Román Torres Dr. Raquel Ledezma Dr. Ronald F. Ziolo Dr. Julio González-Torres 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(7):2493-2505
Two series of 2,5-di(butoxy)phenyleneethynylenes, one halogenated ( n PEC4-X ; n=2, 3, or 4) and the other boron-dipyrromethene (BODIPY) terminated ( n PEC4-By ; n=3, 4, or 5; By=BODIPY), were synthesized monodirectionally by the step-by-step approach and the molecular structure was corroborated by NMR spectroscopy (1H, 13C-DEPTQ-135, COSY, HSQC, HMBC, 11B, 19F) and MALDI-TOF mass spectrometry. The multiplicity and J-coupling constants of 1H, 11B, and 19F/11B NMR signals revealed, in the n PEC4-By series, that the phenyl in the meso position of BODIPY becomes electronically part of the conjugation of the phenyleneethynylene chain, whereas BODIPY is electronically isolated. The photophysical, electrochemical, and theoretical studies confirm this finding because the properties of n PEC4-By are comparable to those of the n PEC4-X oligomers and BODIPY, indicating negligible electron communication between BODIPY and the n PEC4 moieties. Nevertheless, energy transfer (ET) from n PEC4 to BODIPY was rationalized by spectroscopy and theoretical calculations. Its yield decreases with the n PEC4 conjugation length, according to the increase in distance between the two chromophores, resulting in dual emission for the longest oligomer in which ET is quenched. 相似文献
55.
A study was performed to assess the performance of aminoacids immobilized on carbon nanotubes (CNTs) for their employment as a sorbent for solid phase extraction systems. An immobilization method is introduced and the aminoacid l-tyrosine was chosen as a case study. A spectrophotometric study revealed the amount of aminoacid immobilizated on CNTs surface, and it turned to be of 3174 μmol of l-tyr g−1. The material was tested for Co retention using a minicolumn inserted in a flow system. At pH 7.0, the amount of Co retained by the column was of 37.58 ± 3.06 μmol Co g−1 of CNTs. A 10% (v/v) HNO3 solution was chosen as eluent. The pH study revealed that Co binding increased at elevated pH values. The calculation of the mol ratio (moles of Co bound at pH 9 to moles of l-tyr) turned to be 3:1. The retention capacity was compared to other bivalent cations and showed the following tendency: Cu2+ > Ni2+ > Zn2+ ? Co2+. The analytical performance was evaluated and an enrichment factor of 180 was obtained when 10 mL of 11.37 μg L−1 Co solution was loaded onto the column at pH 9.0; reaching a limit of detection (LoD) of 50 ng L−1. The proposed system was successfully applied to Co determination in QC-LL2 standard reference material (metals in natural water). 相似文献
56.
Griselda Deelstra Alexandre Petkovic Michèle Vanmaele 《Journal of Computational and Applied Mathematics》2010,233(11):2814-2830
Asian options, basket options and spread options have been extensively studied in the literature. However, few papers deal with the problem of pricing general Asian basket spread options. This paper aims to fill this gap. In order to obtain prices and Greeks in a short computation time, we develop approximation formulae based on comonotonicity theory and moment matching methods. We compare their relative performances and explain how to choose the best approximation technique as a function of the Asian basket spread characteristics. We also give explicitly the Greeks for our proposed methods. In the last section we extend our results to options denominated in foreign currency. 相似文献
57.
The dynamic behavior close to a non-resonant double Hopf bifurcation is analyzed via a frequency-domain technique. Approximate expressions of the periodic solutions are computed using the higher order harmonic balance method while their accuracy and stability have been evaluated through the calculation of the multipliers of the monodromy matrix. Furthermore, the detection of secondary Hopf or torus bifurcations (Neimark–Sacker bifurcation for maps) close to the analyzed singularity has been obtained for a coupled electrical oscillatory circuit. Then, quasi-periodic solutions are likely to exist in certain regions of the parameter space. Extending this analysis to the unfolding of the 1:1 resonant double Hopf bifurcation, cyclic fold and torus bifurcations have also been detected in a controlled oscillatory coupled electrical circuit. The comparison of the results obtained with the suggested technique, and with continuation software packages, has been included. 相似文献
58.
Raúl Quijada Jaime Retuert Juan L. Guevara René Rojas Marcela Valle Pilar Saavedra Humberto Palza Griselda B. Galland 《Macromolecular Symposia》2002,189(1):111-126
Ethylene, propylene and α-olefins were homo- and copolymerized in the presence of a series of homogeneous catalytic systems consisting of methylaluminoxane (MAO) and group IV metallocenes such as Et(Ind)2ZrCl2 (I), Me2Si(Ind)2ZrCl2 (II), Et(2-Me-Ind)2ZrCl2 (III), Ph2C(Flu)(Cp)ZrCl2 (IV). It was found that the catalytic activity, the incorporation of comonomer in the case of copolymers, and the microstructure of the polymers depend on the catalyst's structure. For heterogeneous catalysts, several supports based on metal oxide compounds have been investigated, with special emphasis in those obtained by the sol-gel preparation technique. The homo- and copolymerization of the monomers in the homogeneous systems studied where also investigated using the same catalyst system, but in a heterogeneous medium. Comparative results from the homogeneous and heterogeneous systems are presented and discussed. 相似文献
59.
Gabriela Leyva Griselda Polla María Teresa Garland Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(11):m534-m536
A new barium acetate phase, di‐μ5‐acetato‐tri‐μ4‐acetato‐tri‐μ3‐acetato‐tri‐μ2‐acetato‐μ2‐acetato‐triaquahemiaquahexabarium(II), of analytical formula [Ba6(C2H3O2)12(H2O)3.5], is described. The asymmetric unit contains six independent Ba centres with coordination numbers varying from 7 to 10 arising from bonding to 12 crystallographically independent acetate ligands and four molecules of water, one of which is disordered over two sites both of occupancy 0.5. Bonding to the acetate ligands creates a completely connected three‐dimensional structure. All H atoms of the water molecules participate in hydrogen bonding. 相似文献
60.
Andrs E. Ciolino Griselda Barrera Galland María Lujn Ferreira Marcelo A. Villar 《Journal of polymer science. Part A, Polymer chemistry》2004,42(10):2462-2473
Polyethylene–poly(dimethylsiloxane) copolymers were synthesized in solution from an ethylene monomer and an ω‐vinyl poly(dimethylsiloxane) (PDMS) macromonomer at 363 and 383 K with EtInd2ZrCl2/methylaluminoxane as a catalyst. The copolymers obtained were characterized with Fourier transform infrared spectroscopy, 1H and 13C NMR, size exclusion chromatography, and differential scanning calorimetry. The rheological properties of the molten polymers were determined under dynamic shear flow tests at small‐amplitude oscillations, whereas the physical arrangement of the phase domains was analyzed with scanning electron microscopy (SEM)/energy dispersive X‐ray (EDX). The analysis of the catalyst activity and the resulting polymers supported the idea of PDMS blocks or chains grafted to polyethylene. The changes in the rheological behavior and the changes in the Fourier transform infrared and NMR spectra were in agreement with this proposal. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2462–2473, 2004 相似文献