Página 1 dos resultados de 93 itens digitais encontrados em 0.003 segundos

Effect of cerium (IV) ions on the anticorrosion properties of siloxane-poly(methyl methacrylate) based film applied on tin coated steel

SUEGAMA, P. H.; SARMENTO, V. H. V.; MONTEMOR, M. F.; BENEDETTI, A. V.; MELO, H. G. de; AOKI, I. V.; SANTILLI, C. V.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.26%
This work investigates the influence of the addition of cerium (IV) ions on the anticorrosion properties of organic-inorganic hybrid coatings applied to passivated tin coated steel. In order to evaluate the specific effect of cerium (IV) addition on nanostructural features of the organic and inorganic phases of the hybrid coating, the hydrolytic polycondensation of silicon alkoxide and the radical polymerization of the methyl methacrylate (MMA) function were induced separately. The corrosion resistance of the coatings was evaluated by means of linear polarization, Tafel type curves and electrochemical impedance measurements. The impedance results obtained for the hybrid coatings were discussed based on an electrical equivalent circuit used to fit the experimental data. The electrochemical results clearly showed the improvement of the protective properties of the organic-inorganic hybrid coating mainly when the cerium (IV) was added to the organic phase solution precursor, which seemed to be due to the formation of a more uniform and densely reticulated siloxane-PMMA film. (C) 2010 Elsevier Ltd. All rights reserved.; FAPESP[05/51851-4]; FAPESP[07/53073-4]; CNPq[310860/2005-9]; CNPq[300728/2007-7]; CNPq[305073/2008-7]; CAPES[BEX-3167-08-9]

Influence of cerium (IV) ions on the mechanism of organosilane polymerization and on the improvement of its barrier properties

SUEGAMA, P. H.; MELO, H. G. de; BENEDETTI, A. V.; AOKI, I. V.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.2%
In this work, the effect of cerium (IV) ammonium nitrate (CAN) addition on the polymerization of bis-[triethoxysilyl]ethane (BTSE) film applied on carbon steel was studied. The electrochemical characterization of the films was carried out in 0.1 mol L(-1) NaCl solution by open-circuit potential measurements, anodic and cathodic polarization curves and electrochemical impedance spectroscopy (EIS). Morphological and chemical characterization were performed by atomic force microscopy (AFM), contact angle measurements, infrared-spectroscopy, nuclear magnetic resonance and thermogravimetric analysis. The results have clearly shown the improvement on the protective properties of the Ce(4+) modified film as a consequence of the formation of a more uniform and densely reticulated silane film. A mechanism is proposed to explain the accelerating role of Ce(4+) ions on the cross-linking of the silane layer. (C) 2008 Elsevier Ltd. All rights reserved.

Stabilization of polyaniline by the incorporation of magnetite nanoparticles

Jaramillo-Tabares, Beatriz E.; Isaza, Franklin Jaramillo; de Torresi, Susana I. Cordoba
Fonte: ELSEVIER SCIENCE SA; LAUSANNE Publicador: ELSEVIER SCIENCE SA; LAUSANNE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
26.51%
Nanocomposites obtained from the polymerization of aniline in the presence of nanoparticles of magnetite (Fe3O4) have been investigated in previous studies. However, there is a lack of information available on the redox interaction of the nanoparticle/conductive polymer couple and the stability that such an oxide can give to the organic phase. In this work, Fe3O4 nanoparticles were incorporated into a PANi matrix by the in-situ oxidative polymerization method. A combination of X-ray diffraction, Mossbauer spectroscopy, transmission electronic microscopy, UV-visible spectroscopy as well as the cyclic voltammetric and Raman spectroscopy techniques, was used to understand the redox effect that the partially oxidized nanoparticles produced on the polymer. It was found that magnetite greatly stabilised PANi, mainly by enhancing the Leucoemeraldine/Emeraldine redox couple and also by reducing the bipolaronic state. (C) 2011 Elsevier B.V. All rights reserved.; Programa de SostenibilidadUdeA; Programa de SostenibilidadUdeA

Coordenação a centros de rutênio e polimerização via metátese de um novo monômero-ligante do tipo norborneno-piridina; Coordination to ruthenium centers and polymerization via metathesis of a new monomer-ligand of type norbornene-pyridine

Ferreira, Daniele Marcondes
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 09/03/2012 PT
Relevância na Pesquisa
26.27%
O monômero-ligante (3amdpy)2NBE foi sintetizado e caracterizado por análise elementar (CHN), infravermelho e RMN (1H e 13C), tratando-se de um novo ligante quelante que apresenta duas piridinas conectadas ao monômero norborneno via grupos amidas. Esse monômero-ligante foi ligado a um centro de Ru(II)-polipiridínico e o complexo resultante foi caracterizado por análise elementar (CHN), infravermelho, RMN (1H e 13C) e espectrometria de massa como sendo cis-[Ru(bpy)2((3amdpy)2NBE)](PF6)2. O espectro eletrônico do novo complexo apresentou absorção no visível em 460 e 480 nm. Essa bandas são típicas de MLCT com valores de ε na ordem de 104 L cm-1 mol-1. O voltamograma cíclico em CH3CN apresentou um processo redox com potencial de meia-onda de 0,89 V vs Ag/AgCl que é de 60 unidades mais positivo do que o complexo precursor cis- [RuCl2(bpy) 2]. O novo metalo-monômero foi submetido à irradiação a λ= 480 nm, demonstrando ser fotoquimicamente inerte em DMSO, CH3CN, acetona e DMF. A emissão do complexo obtido variou em função do solvente e apresentou maior intensidade de emissão em acetonitrila (λem= 720 nm). A variação do solvente não levou ao deslocamento do máximo de emissão do complexo. O monômero-ligante foi polimerizado via metátese catalisada por catalisador de Grubbs...

Oxidative stress in sickle cell disease: An overview of erythrocyte redox metabolism and current antioxidant therapeutic strategies

Silva, Danilo Grunig Humberto; Belini Junior, Edis; De Almeida, Eduardo Alves; Bonini-Domingos, Claudia Regina
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1101-1109
ENG
Relevância na Pesquisa
36.09%
Erythrocytes have an environment of continuous pro-oxidant generation due to the presence of hemoglobin (Hb), which represents an additional and quantitatively significant source of superoxide (O2 •-) generation in biological systems. To counteract oxidative stress, erythrocytes have a self-sustaining antioxidant defense system. Thus, red blood cells uniquely function to protect Hb via a selective barrier allowing gaseous and other ligand transport as well as providing antioxidant protection not only to themselves but also to other tissues and organs in the body. Sickle hemoglobin molecules suffer repeated polymerization/depolymerization generating greater amounts of reactive oxygen species, which can lead to a cyclic cascade characterized by blood cell adhesion, hemolysis, vaso-occlusion, and ischemia-reperfusion injury. In other words, sickle cell disease is intimately linked to a pathophysiologic condition of multiple sources of pro-oxidant processes with consequent chronic and systemic oxidative stress. For this reason, newer therapeutic agents that can target oxidative stress may constitute a valuable means for preventing or delaying the development of organ complications. © © 2013 Elsevier Inc. All rights reserved.

Enzymatic polymerization of phenolic compounds

Gonçalves, Idalina; Botelho, C. M.; Paulo, Artur Cavaco
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 25/05/2014 ENG
Relevância na Pesquisa
26.26%
Phenolics are natural compounds which contains hydroxyl group bonded to aromatic hydrocarbon ring. These compounds can be divided into two categories depending on the oxidation state of the central pyran ring: flavonoids and non-flavonoids. It is important to highlight the excellent properties of the phenolic compounds, such as anti-inflammatory, antimicrobial, and antioxidant activity. It has been described that the oxidation of phenolic compounds enhances its antimicrobial properties since the resulting polymers can contribute to the microorganism’s toxification. The polymerization reaction can be achieved by different biocatalysts such as oxidoreductases, namely laccases and peroxidases. Laccases use molecular oxygen as a co-substrate, being therefore the perfect co-substrate. Depending on the structure of the phenolic compound, namely the number of hydroxyl groups, the enzymatic polymerization can be performed via laccase or using laccase-mediator systems (LMSs). On the first reaction, the phenolic compound is oxidized and the resulting phenoxy radicals conduct to polymers formation through recombination processes. On the second method, the phenolic compound oxidation is mediated by redox species yielding the polyphenols formation. Any of these two routes allows the polymerization of phenolic products with enhanced properties.

Conductive cotton prepared by polyaniline in situ polymerization using laccase

Zhang, Ya; Dong, Aixue; Wang, Qiang; Fan, Xuerong; Paulo, Artur Cavaco; Zhang, Ying
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em //2014 ENG
Relevância na Pesquisa
36.3%
The high-redox-potential catalyst laccase, isolated from Aspergillus, was first used as a biocatalyst in the oxidative polymerization of water-soluble conductive polyaniline, and then conductive cotton was prepared by in situ polymerization under the same conditions. The polymerization of aniline was performed in a water dispersion of sodium dodecylbenzenesulfonate (SDBS) micellar solution with atmospheric oxygen serving as the oxidizing agent. This method is ecologically clean and permits a greater degree of control over the kinetics of the reaction. The conditions for polyaniline synthesis were optimized. Characterizations of the conducting polyaniline and cotton were carried out using Fourier transform infrared spectroscopy, UV–vis spectroscopy, cyclic voltammetry, the fabric induction electrostatic tester, and the far-field EMC shielding effectiveness test fixture.

Synthesis and thermal behavior of polyacrylonitrile/vinylidene chloride copolymer

Fleming,Robson; Pardini,Luiz Claudio; Alves,Nilton; Garcia,Elson; Brito Júnior,Carlos
Fonte: Associação Brasileira de Polímeros Publicador: Associação Brasileira de Polímeros
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 EN
Relevância na Pesquisa
26.2%
Polyacrylonitrile fiber encompasses a broad range of products based on acrylonitrile (AN) which is readily copolymerized with a wide range of ethylenic unsaturated monomers giving rise to polymers with different characteristics and applications. Such products can be designed for cost-effective, flame and heat resistant solutions for the textile industry, aircraft and automotive markets. In the present work acrylonitrile was copolymerized with vinylidene chloride (VDC) by conventional suspension polymerization process via redox system, with an initial content of 10%/mass of the VDC monomer. The copolymer average molecular weight was obtained by Gel Permeation Chromatography (GPC) and by intrinsic viscosity analysis. To control the polymerization process continuously, qualitative and quantitative analysis of the chloride content in the PAN AN/VDC copolymer structure was accomplished by using X-ray fluorescence and potentiometric titration techniques. A good correlation was found between these two techniques, leading to a straightforward verification of VDC in the polymer structure. The thermal behavior of PAN AN/VDC copolymer was performed by Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). The results showed that VDC monomers exhibited a nearly stoichiometric reaction with acrylonitrile...

Redox and Activation Status of Monocytes from Human Immunodeficiency Virus-Infected Patients: Relationship with Viral Load

Elbim, C.; Pillet, S.; Prevost, M. H.; Preira, A.; Girard, P. M.; Rogine, N.; Matusani, H.; Hakim, J.; Israel, N.; Gougerot-Pocidalo, M. A.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /06/1999 EN
Relevância na Pesquisa
26.27%
Monocytes are precursors of tissue macrophages, which are major targets of human immunodeficiency virus type 1 (HIV-1) infection. Although few blood monocytes are infected, their resulting activation could play a key role in the pathogenesis of HIV disease by modulating their transendothelial migration and inducing the production of reactive oxygen species (ROS). ROS participate in chronic inflammation, HIV replication, and the apoptosis of immune system cells seen in HIV-infected subjects. Published data on monocyte activation are controversial, possibly because most studies have involved monocytes isolated from their blood environment by various procedures that may alter cell responses. We therefore used flow cytometry to study, in whole blood, the activation and redox status of monocytes from HIV-infected patients at different stages of the disease. We studied the expression of adhesion molecules, actin polymerization, and cellular levels of H2O2, Bcl-2, and thioredoxin. Basal H2O2 production correlated with viral load and was further enhanced by bacterial N-formyl peptides and endotoxin. The enhanced H2O2 production by monocytes from asymptomatic untreated patients with CD4+ cell counts above 500/μl was associated with a decrease in the levels of Bcl-2 and thioredoxin. In contrast...

Polymerization of Monolignols by Redox Shuttle–Mediated Enzymatic Oxidation: A New Model in Lignin Biosynthesis I

Önnerud, Hans; Zhang, Liming; Gellerstedt, Göran; Henriksson, Gunnar
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /08/2002 EN
Relevância na Pesquisa
26.42%
Lignin is one of the most abundant biopolymers, and it has a complex racemic structure. It may be formed by a radical polymerization initiated by redox enzymes, but much remains unknown about the process, such as how molecules as large as enzymes can generate the compact structure of the lignified plant cell wall. We have synthesized lignin oligomers according to a new concept, in which peroxidase is never in direct contact with the lignin monomers coniferaldehyde and coniferyl alcohol. Instead, manganese oxalate worked as a diffusible redox shuttle, first being oxidized from Mn(II) to Mn(III) by a peroxidase and then being reduced to Mn(II) by a simultaneous oxidation of the lignin monomers to radicals that formed covalent linkages of the lignin type. Furthermore, a high molecular mass polymer was generated by oxidation of coniferyl alcohol by Mn(III) acetate in a dioxane and water mixture. This polymer was very similar to natural spruce wood lignin, according to its NMR spectrum. The possible involvement of a redox shuttle/peroxidase system in lignin biosynthesis is discussed.

A redox-sensitive loop regulates plasminogen activator inhibitor type 2 (PAI-2) polymerization

Wilczynska, Malgorzata; Lobov, Sergei; Ohlsson, Per-Ingvar; Ny, Tor
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
Publicado em 15/04/2003 EN
Relevância na Pesquisa
26.51%
Plasminogen activator inhibitor type 2 (PAI-2) is the only wild-type serpin that polymerizes spontaneously under physiological conditions. We show that PAI-2 loses its ability to polymerize following reduction of thiol groups, suggesting that an intramolecular disulfide bond is essential for the polymerization. A novel disulfide bond was identified between C79 (in the CD-loop) and C161 (at the bottom of helix F). Substitution mutants in which this disulfide bond was broken did not polymerize. Reactive center loop peptide insertion experiments and binding of bis-ANS to hydrophobic cavities indicate that the C79–C161 disulfide bond stabilizes PAI-2 in a polymerogenic conformation with an open A-β-sheet. Elimination of this disulfide bond causes A-β-sheet closure and abrogates the polymerization. The finding that cytosolic PAI-2 is mostly monomeric, whereas PAI-2 in the secretory pathway is prone to polymerize, suggests that the redox status of the cell could regulate PAI-2 polymerization. Taken together, our data suggest that the CD-loop functions as a redox-sensitive switch that converts PAI-2 between an active stable monomeric and a polymerogenic conformation, which is prone to form inactive polymers.

Dually responsive multiblock copolymers via RAFT polymerization: Synthesis of temperature- and redox-responsive copolymers of PNIPAM and PDMAEMA

You, Ye-Zi; Zhou, Qing-Hui; Manickam, Devika Soundara; Wan, Lei; Mao, Guang-Zhao; Oupický, David
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
Relevância na Pesquisa
26.36%
We report synthesis of temperature- and redox-responsive multiblock copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization. Well-defined α,ω-bis(dithioester)-functionalized poly(N-isopropylacrylamide) (PNIPAM) and poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) were prepared using 1,4-bis(thiobenzoylthiomethyl)benzene and 1,4-bis(2-(thiobenzoylthio)prop-2-yl)benzene as RAFT agents, respectively. Dually responsive multiblock copolymers were synthesized in a single aminolysis/oxidation step from the α,ω-bis(dithioester)-terminated PNIPAM and PDMAEMA. The copolymers and their stimulus-responsive behavior were characterized by size exclusion chromatography, NMR, light scattering and atomic force microscopy. Due to the presence of redox-sensitive disulfide bonds between the blocks, the copolymers were readily reduced to the starting polymer blocks. The presence of temperature-responsive PNIPAM blocks provided the copolymers with the ability to assemble into core-shell nanostructures with hydrophobic PNIPAM as a core and cationic PDMAEMA as stabilizing shell when above the phase transition temperatures of PNIPAM. The temperature-induced assembly of the copolymers also showed substantial pH sensitivity. The phase transition temperature increased with decreasing pH...

Enzyme-Mediated Redox Initiation for Hydrogel Generation and Cellular Encapsulation

Johnson, Leah M.; Fairbanks, Benjamin D.; Anseth, Kristi S.; Bowman, Christopher N.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 09/11/2009 EN
Relevância na Pesquisa
26.43%
A rapid, water-soluble enzyme-mediated radical chain initiation system involving glucose oxidase and Fe+2 generated hydrogels within minutes at 25°C and in ambient oxygen. The initiation components were evaluated for their effect on polymerization rates of hydroxyethyl acrylate-poly(ethylene glycol)575 diacrylate comonomer solutions using near-infrared spectroscopy. Increasing glucose concentration increased polymerization rates until reaching a rate plateau above 1 × 10−3M of glucose. A square root dependence of the initial polymerization rate on Fe+2 concentration was observed between 1.0 × 10−4M and 5.0 × 10−4M of Fe+2 whereupon excess Fe+2 reduced final acrylate conversions. The glucose oxidase-mediated initiation system was employed for encapsulation of fibroblasts (NIH3T3s) into a poly(ethylene glycol) tetra-acrylate (Mn~20,000) hydrogel scaffold demonstrating 96% (±3%) viability at 24 hours post-encapsulation. This first use of enzyme-mediated redox radical chain initiation for cellular encapsulation demonstrates polymerization of hydrogels in situ with kinetic control, minimal oxygen inhibition issues and utilization of low initiator concentrations.

Formation of three-dimensional hydrogel multilayers using enzyme-mediated redox chain initiation

Johnson, Leah M.; DeForest, Cole A.; Pendurti, Aishwarya; Anseth, Kristi S.; Bowman, Christopher N.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/2010 EN
Relevância na Pesquisa
26.6%
Enzyme-mediated redox chain initiation involving glucose oxidase (GOX) was employed in an iterative solution dip-coating technique to polymerize multiple, three-dimensional hydrogel layers using mild aqueous conditions at ambient temperature and oxygen levels. To our knowledge, sequential enzyme-mediated dip-coating resulting in an interfacial radical chain polymerization and subsequent formation of three-dimensional hydrogel layers has not been previously explored. Conformal, micron-scale, uniform poly(ethylene glycol) (PEG)-based hydrogel layers were polymerized within seconds and remained securely associated after incubation in water for 16 weeks. Incorporation of either small molecules (i.e., rhodamine-B acrylate, fluorescein acrylate) or fluorescent nanoparticles into crosslinked hydrogel layers during the polymerization reaction was also achieved. The encapsulation of 0.2 μm- diameter nanoparticles into hydrogels during polymerization of a 2-hydroxyethyl acrylate (HEA)/PEG575 diacrylate monomer formulation, using the GOX-mediated initiation, resulted in minimal effects on polymerization kinetics, with final acrylate conversions of 95% (±1%) achieved within minutes. The temporal control and spatial localization afforded by this interfacial redox approach resulted in the polymerization of uniform secondary layers ranging between 150 (±10) μm and 650 (±10) μm for 15 and 120 s immersion times...

Control of Poly(N-isopropylacrylamide) Microgel Network Structure by Precipitation Polymerization near the Lower Critical Solution Temperature

Hu, Xiaobo; Tong, Zhen; Lyon, L. Andrew
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.27%
Poly(N-isopropylacrylamide)(pNIPAm) microgels were synthesized by precipitation polymerization at temperatures ranging from 37 °C to 45 °C using the redox initiator system ammonium persulfate (APS)/N,N,N’,N’-tetramethylethylenediamine (TEMED), or the photoinitiator 2,2′-azobis(amidinopropane) dihydrochloride (V50). Photon correlation spectroscopy (PCS) and atomic force microscopy (AFM) studies revealed that spherical microgels with narrow size dispersities can be obtained with these methods, and that the resultant microgels have volume phase transition behaviors expected from their compositions. Additionally, the low temperature, redox initiator strategy produces microgels devoid of self-cross-linking, thereby permitting the synthesis of completely degradable microgels when using N,N’-(1,2-dihydroxyethylene)bisacrylamide (DHEA) as a cleavable cross-linker. We also demonstrate the potential utility of the approach in bioconjugate syntheses; in this case avidin immobilization is demonstrated by one-pot copolymerization at low temperature.

Kinetics of interfacial radical polymerization initiated by a glucose-oxidase mediated redox system

Shenoy, Raveesh; Bowman, Christopher N.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.3%
The reaction and coating kinetics for the glucose oxidase initiated interfacial polymerization are elaborated. The interfacial film grows rapidly and linearly with time, producing time-dependent controllable conformal coating thicknesses of up to a millimeter in less than 4 minutes. Bulk polymerization was only observed when the immersing media was stirred to induce higher mass transport rates. The dramatically different film thicknesses observed between different concentrations of glucose in the hydrogel and iron in the bulk media are demonstrated to be a result of an initial rapid growth phase following which the film grows at the same rate nearly independent of either the glucose or iron concentration. The polymerization rate and hence the thickness growth rate in this initial phase saturate at glucose and iron concentrations above 0.8 M and 0.63 mM, respectively. At iron concentrations above 0.05 mM, the film thickness at the end of 3 hours of reaction monotonically decreased with increasing iron concentration from 5.7 mm to 4.2 mm. The glucose oxidase is trapped by the growing polymerization front and can be used as the sole enzymatic precursor to coat a second polymeric layer. However, the rate of film growth of the second layer is 14-fold lower than the rate of film growth when bulk enzyme is present during the second stage coating process.

Redox Initiation of Bulk Thiol-Ene Polymerizations

Cole, Megan A.; Jankousky, Katherine C.; Bowman, Christopher N.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.63%
The unique formation-structure-property attributes and reaction behavior of the thiol-ene “click” reaction have been explored extensively for photochemically and thermally initiated reactions but have been much less explored for redox initiation. Therefore, the objective of this work is to characterize fully the impact of the initiation system, monomer structure, degree of functionalization, and inhibitor level on the redox-mediated thiol-ene polymerization rate and behavior. Moreover, this study confirms the ability of redox initiation to achieve full conversion of desired thiol-ene “click” products for small molecules in solution. For the multifunctional thiol-ene systems, polymerization rate was shown to be comparable to photo- and thermally initiated systems, but with the additional advantages of unlimited depth of cure and mild reaction conditions. Additionally, the network properties of the redox-initiated thiol-ene systems were on par with a photocured material formulated with identical monomers and radical initiating potential. Lastly, control over the polymerization rate and preceding induction period was garnered from the concentration of inhibitor included in the reaction mixture. The mechanism of action of quinone inhibition in redox-mediated thiol-ene polymerizations is shown to depend on both the presence of an aniline reducing agent and the concentration of inhibitor...

Iron-Based Redox Polymerization of Acrylic Acid for Direct Synthesis of Hydrogel/Membranes, and Metal Nanoparticles for Water Treatment

Hernández, Sebastián; Papp, Joseph K.; Bhattacharyya, Dibakar
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.1%
Functionalized polymer materials with ion exchange groups and integration of nano-structured materials is an emerging area for catalytic and water pollution control applications. The polymerization of materials such as acrylic acid often requires persulfate initiator and a high temperature start. However, is generally known that metal ions accelerate such polymerizations starting from room temperature. If the metal is properly selected, it can be used in environmental applications adding two advantages simultaneously. This paper deals with this by polymerizing acrylic acid using iron as accelerant and its subsequent use for nanoparticle synthesis in hydrogel and PVDF membranes. Characterizations of hydrogel, membranes and nanoparticles were carried out with different techniques. Nanoparticles sizes of 30–60 nm were synthesized. Permeability and swelling measurements demonstrate an inverse relationship between hydrogel mesh size (6.30 to 8.34 nm) and membrane pores (222 to 110 nm). Quantitative reduction of trichloroethylene/chloride generation by Fe/Pd nanoparticles in hydrogel/membrane platforms was also performed.

Synthesis, Structure and Reactivity Studies of Nickel Pincer Complexes and Evaluating Redox Non-innocence of the Ligand

Adhikari, Debashis
Fonte: [Bloomington, Ind.] : Indiana University Publicador: [Bloomington, Ind.] : Indiana University
Tipo: Doctoral Dissertation
EN
Relevância na Pesquisa
36.32%
Thesis (Ph.D.) - Indiana University, Chemistry, 2009; Bimetallic cores are ubiquitous in natural enzymes and presently being used in several important chemical transformations such as epoxidation of olefins or stereoselective polymerization of oxiranes. To understand the nature of interaction between two metal centers in a bimetallic core we synthesized the diamond core, [Ni(2-PNP)]2 (PNP− = N[2-P(CHMe2)2-4-MeC6H3]2) and observed that the two Ni(I) metal centers are feebly interacting, particularly in an antiferromagnetic manner, despite an extremely short distance (2.3288(7) Å) between them. The molecule behaves as a masked Ni(I) synthon and can perform the cleavage of a plethora of homonuclear or heteronuclear bonds to incorporate rare functionalities onto nickel. A current interest has been surged in group transfer reactions employing nickel reagents since its higher congeners, namely Pd and Pt are too expensive. Transition metal mediated transfer of boryls to aromatic and aliphatic hydrocarbons to engender corresponding aryl boronic esters appears to be very promising given the widespread utility of the ester in C−C bond coupling reactions. In the attempt of nickel mediated borylation we discovered a simple route to engender formation of a stable...

Living/controlled Polymerization Conducted in Aqueous Based Systems

Simms, Ryan W.
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 3221405 bytes; application/pdf
EN; EN
Relevância na Pesquisa
36.39%
In the last decade processes known as living/controlled radical polymerizations (L/CRP) have been developed which permit the synthesis of high-value specialty polymers. Currently, the three processes that have demonstrated the most potential are: reverse addition fragmentation chain transfer polymerization (RAFT), atom transfer radical polymerization (ATRP) and stable free radical polymerization (SFRP). While each process has their strengths and weaknesses with regard to specific polymers and architecture, the viability of these systems to industrial scale production all lie in the ability to perform the polymerization in a water based system because of process, environmental and economic advantages. The most effective method of controlling the polymerization of vinyl acetate in bulk has been RAFT. We have developed a miniemulsion RAFT polymerization using the xanthate methyl (ethoxycarbonothioyl)sulfanyl acetate. The miniemulsion is stabilized with 3 wt% sodium lauryl sulfate, initiated with the azo-based water-soluble VA-060. The main focus of this research was adapting ATRP to a miniemulsion system. It was determined that ionic surfactants can be successfully employed in emulsion-based ATRP. The cationic surfactant cetyltrimethylammonium bromide provides excellent stability of the latex over a range of surfactant loadings (allowing the particle size to be easily manipulated)...