Navegando por Palavras-chave "Copolymer"
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- ItemAcesso aberto (Open Access)Métodos alternativos para proteção à corrosão da liga de alumínio 2024-T3(Universidade Federal de São Paulo, 2015-03-06) Xavier, Thiago Henrique Andrade [UNIFESP]; Camilo, Fernanda Ferraz [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)This work presents the anti-corrosion behavior of a soluble copolymer of polyaniline (PAni), called poly (phenylene sulfide phenylamine) - PPSA, deposited on the Al 2024-T3 alloy. The motivation for the use of this copolymer is that it shows electroactivity similar to PAni, but it is soluble in various organic solvents, allowing its deposition by casting. Additionally, the anti-corrosion performance of polypyrrole (PPy) electrodeposited in ionic liquid was also studied. The use of ionic liquid as electrolyte was motivated because the Al alloy is not corroded in this medium. The efficiency of PPSA and PPy films in the corrosion protection of Al 2024-T3 alloy was investigated by open circuit potential tests, potentiodynamic polarization curves, electrochemical impedance spectroscopy, immersion tests and scanning electron microscopy. The PPSA film, in reduced form, produced with six subsequent depositions of its solution in tetrahydrofuran (4 mg/mL) resulted in the best performance against corrosion. Thicker films do not show satisfactory results due to their lower adhesion on the Al alloy. The PPSA film with six depositions was more compact and homogeneous, which afforded better performance in the corrosion protection, probably preventing the penetration of aggressive species, such as chloride ions. The PPy was efficiently electrodeposited on the Al 2024-T3 alloy by cyclic voltammetry. The morphology of this film was dependent on the scan rate used. The micrographs showed that in all experimental conditions, the films are quite porous, giving low efficiency of these coatings in the corrosion protection of the alloy.
- ItemSomente MetadadadosNovel Copoly(Styrene-Divinylbenzene)-Resins with Different Phenylmethylamine Groups for Use in Peptide Synthesis Method(Bentham Science Publ Ltd, 2015-01-01) Souza, Sinval Estevam Gregorio de [UNIFESP]; Malavolta, Luciana [UNIFESP]; Cilli, Eduardo Maffud [UNIFESP]; Schreier, Shirley [UNIFESP]; Jubilut, Guita Nicolaewsky [UNIFESP]; Nakaie, Clovis Ryuichi [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); Santa Casa Sao Paulo Sch Med Sci; Unesp; Universidade de São Paulo (USP)Differently than the 4-methylbenzhydrylamine-resin (MBHAR) which contains a methyl group coupled to the phenylmethylamine-functionalized copoly(styrene-divinilbenzene) structure, alternative resins containing the electron-donating 4-tert-butyl-(BUBHAR) or the electron-withdrawing 2-chloro-(ClBHAR) and 2,4-chloro-(diClBHAR) groups were developed as potential supports for carboxamide peptide synthesis. Initially, a time-course investigation of HF cleavage reaction (0 degrees C) with these resins bearing the vasoconstrictor angiotensin II (AngII, DRVYIHPF) or its Gly(8)-AngII analogue revealed that the peptide-BUBHAR linkage is much more labile than those with ClBHAR or diClBHAR. HF cleavage times of near 2 h or longer than 24 h were needed for complete removal of peptide chains from these two classes of resin, respectively. By including MBHAR and benzhydrylamine-resins (BHAR) in this comparative study, the decreasing order of acid stability of the peptidyl-resin linkage was diClBHAR > ClBHAR > BHAR > MBHAR similar to BUBHAR. The same stability order was observed for the HCl/ propionic acid hydrolysis reaction (130 degrees C) with the Phe-or Gly-resins. These findings thus suggest that ClBHAR and diClBHAR are not appropriate for use in peptide synthesis. Nevertheless, these supports could still be tested as stationary phases for affinity chromatography. When placed into more apolar solvents, the beads of all of these resins exhibited a greater swelling (as measured by a microscope) or higher mobility of the polymer matrix (as measured with EPR experiments using spin-labeled beads). Moreover, under the latter approach, BUBHAR displayed a comparatively higher solvation degree than did MBHAR (in DCM, DMF and NMP), with slightly higher peptide synthesis yields as well.
- ItemAcesso aberto (Open Access)Preparação de nanopartículas de prata em meio alcoólico e utilizando moldes rígidos de silica mesoporosa(Universidade Federal de São Paulo, 2014-06-06) Oliveira, Roselaine da Silva [UNIFESP]; Camilo, Fernanda Ferraz [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)In this work the preparation and characterization of non-aqueous dispersions of silver nanoparticles (AgNP) prepared with 1-butanol, which acted as both solvent and reducing agent of Ag+ ions, obtained from silver nitrate or silver tetrafluoroborate were shown. A biocompatible block copolymer of polyether and polyamide (PEBA) was used as dispersion agent. The goal was to obtain non-aqueous dispersions of silver nanoparticle highly concentrated and stable. It is noteworthy to mention that in aqueous media, the silver nanoparticles concentration is relatively low (around 30 mg/L - 0.47 mM) and this dispersions does not show compatibility with hydrophobic surfaces such as PTFE, silicone, polyvinyl chloride (PVC) and polyethylene (PE). After finding the best experimental conditions (reactant concentration, type of silver salt, reaction time, percentage of stabilizer), it was produced a hydrophobic dispersion of silver nanoparticles, which is stable for more than 6 months, with a concentration of 5 mM, which is higher than that obtained in water. The AgNP diameters vary from 5 to 10 nm. The dispersion showed antimicrobial activity against Staphylococcus aureus and Escherichia coli even at low concentration. In addition, it was prepared and characterized silver nanoparticles immobilized into a mesoporous silica, called MCM-41 (with pores non-functionalized and functionalized surface with –SH and –SO3-), using 1-butanol as reducing agent of the silver ions, obtained from silver nitrate. 1-butanol was able to reduce the incorporated Ag+ in the silicas pores. A partial disordering of the silica has been observed mainly in the composite prepared with pure MCM-41. It was also found that there are silver nanoparticles inside the silica’s pores and the composite with –SH groups has the greater amount of silver. The catalytic activity of these composites was evaluated by the reduction of p-nitrophenol to p-aminophenol in the presence of sodium borohydride, but the MCM-41/Ag composite showed the highest catalytic activity for this test.
- ItemSomente MetadadadosSíntese E Avaliação Do Homopolímero Poli(3-Hexiloxitiofeno) E Seu Copolímero Com Poli(3-Tiofeno Acetato De Metila) Para Aplicações Optoeletrônicas(Universidade Federal de São Paulo (UNIFESP), 2017-08-28) Ribeiro, Debora Aparecida [UNIFESP]; Carvalho, Rossano Lang [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)In this work, we present a systematic study of two different polythiophene derivatives and their random copolymers polymerized by the modified Sugimoto route; a ether-substituted thiophene, poly(3-hexyloxythiophene) - P3HOT and the other a ester-substituted thiophene, poly(3-thiophene methyl acetate) - P3TMA. The modified Sugimoto route consisted of the use of a solvent/non-solvent pair as a reaction medium in order to achieve a higher polymeric yield. The starting monomers 3HOT and 3TMA are not found commercially and thus, the syntheses under particular conditions were necessary to achieve the central aim of the investigation: to obtain a material with broadband absorption property in the spectral region of the ultraviolet-visible light for optoelectronic applications. For the random copolymers P(3HOTx-co-3TMAy) the synthesis was based on three different mass percentages: 25, 50 and 75 % w/w. The monomers and homopolymers were characterized in detail in order to elucidate their chemical structures and properties. By means of structural and thermal characterizations, it was possible to identify the material formation, to infer the coupling types, to obtain information about homogeneity of polymeric chain as well as degradation onset temperature and thermal stability data. The same systematic study was used for a selected copolymer. From the optical characterization results the copolymer P(3HOT75-co-3TMA25) was selected by the criteria of best performance of broadband photoabsorption, becoming the only one characterized in the other analyzes. We also evaluated the influence of two solvents (chloroform and tetrahydrofuran) on the optical transition π-π* of each material. Fluorescence spectra in emission and excitation regimes showed electronic states of the selected copolymer different from those observed in the homopolymers. These excited states were better defined when the solvent was the tetrahydrofuran. In addition, the best solvent in terms of solubility (chloroform) was used in the preparation of thin films (doped and non-doped) on quartz substrates. The doping effect on the optical properties of the polythiophene derivatives was evaluated by the intentional addition of TCNQ (7,7,8,8-tetracyanoquinodimethane) in a 1:1 mass ratio (w/w). The TCNQ one behaved as an electron acceptor molecule and the polymers as electron donors, exhibiting interesting absorbance and fluorescence quenching results when solubilized in chloroform. Quenching was not observed when in the form of films. The electrochemical characterization showed the side chain effects through the values of oxidation potential for each material. The results indicate that the onset oxidation potential of PT3MA and the selected copolymer occur at much more cathodic potentials than that of P3HOT. This demonstrates the strong electron donor character of hexyloxy chains, confirmed by the lower oxidation potential. As a consequence, the HOMO level of P3HOT was higher than in the other polymers. The electrical resistance results have indicated conductivities between 10-10 and 10-11 S/cm, characteristic of undoped polythiophenes. Finally, based on the study carried out we infer that P(3HOT75-co-3TMA25) copolymer is a promising material for applications in organic photovoltaic devices because it exhibits a broadband light-absorbing behavior in the range of 350-600 nm.