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排序方式: 共有1666条查询结果,搜索用时 15 毫秒
91.
Víctor M. Ovando‐Medina Paola E. Díaz‐Flores René D. Peralta Eduardo Mendizábal Gladis Y. Cortez‐Mazatan 《应用聚合物科学杂志》2013,127(4):2458-2464
Vinyl acetate (VAc) and butyl acrylate (BuA) were copolymerized in heterophase by a semicontinuous process (unseeded) and compared with the seeded semicontinuous microemulsion polymerization of the same monomers. A mixture of sodium dodecyl sulfate (SDS) and poly(ethylene oxide) dodecyl ether (Brij‐35®) were used as surfactants. The effects of monomer addition rate (Ra) and surfactants concentrations (4 or 1 wt % with respect to the initial mixture of reaction) on polymer and latex properties were studied. High copolymer content latexes (24–36 wt %) with average particle diameters (Dp) from 38 to 55 nm and relatively narrow particle size distributions, high polymerization rates, weight ratios of polymer to surfactant (P/S) from 13.3 to 32.8 were obtained. The number‐average molecular weights (Mn) were between 96,000 and 188,000 g/mol. Homogeneous copolymer compositions were obtained throughout the reaction for both, seeded and unseeded processes, which is not possible by the usual batch microemulsion process. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
92.
Fausto Puntoriero Giacomo Bergamini Paola Ceroni Vincenzo Balzani Fritz Vögtle 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(1):189-194
Starting from 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane, we have prepared two compounds by replacing the amine hydrogens
with naphthyl or 3,5-bis(2′-oxymethylnaphthyl)benzyl units. The absorption and emission spectra of compounds 2 (N,N′-bis(2-naphthylmethyl)-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane) and 3 (N,N′-bis[3,5-bis(2′-oxymethylnaphthyl)benzyl]-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane) have been studied in CH3CN:CH2Cl2 1:1 (v/v) solution. For comparison purposes, the spectroscopic properties of N-methyl(2-methylnaphthalene)ethylamine (1) have also been investigated. For each compound, the absorption spectra are qualitatively very similar to that of naphthalene,
with molar absorption coefficients as expected for the presence of one (1), two (2), and four (3) naphthyl chromophoric groups. The fluorescence spectra, however, are quite different from that of naphthalene. The naphthalene-type
fluorescence (λmax = 337 nm) is strongly quenched, particularly for compounds 1 and 2 which also exhibit a broad emission band in the visible region (λmax ≈ 480 nm) assigned to a low lying charge-transfer excited state. In the case of compound 3, a quenched naphthalene-type band is accompanied by weak exciplex and excimer emissions. Upon titration with CF3SO3H, the charge transfer bands of 1 and 2 and the exciplex emission of 3 disappear and the naphthalene-type bands regain intensity. Titration plots show that in compounds 2 and 3 the protonation of the two nitrogens occurs stoichiometrically in two distinct steps. Titration with Zn2+ gives rise to 2.Zn2+ and 3.Zn2+ complexes.
This article is dedicated to Professor Dedier Astruc. 相似文献
93.
Use of ionic liquids based on phosphonium salts for preparing biocomposites by in situ polymerization
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A sodium montmorillonite, Dellite HPS, was modified with ionic liquids based on phosphonium salts, such as octadecyltriphenylphosphonium tetrafluoroborate and octadecyltriphenylphosphonium bromide. Thanks to their high thermal stability, these salts can be used during in situ polymerization, a method that favors the achievement of a good dispersion of the clay. Poly(1,4‐dimethylcyclohexane adipate) (PCHA), was chosen as an example of aliphatic polyester which can be a suitable matrix for new biocomposites with organo‐clays. The organo modified clays prepared were characterized by X‐ray diffraction (XRD), ATR‐FTIR spectroscopy, and thermal gravimetric analysis (TGA) while biocomposites were analyzed in terms of molecular structure, thermal and thermomechanical properties. The degree of dispersion of the clays in the polymer matrix was studied by XRD. The results show that the clays are well dispersed in the biocomposites, despite an intercalated structure highlighted by XRD analysis. Moreover, the clays confer a certain improvement in mechanical properties to the final materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42467. 相似文献
94.
Cold groundwater temperatures and conductive heat flow in the Mt. Amiata geothermal area, Tuscany, Italy 总被引:1,自引:0,他引:1
Giovanni Chiodini Paola Comodi Stefano Giaquinto Bruno Mattioli Anna Rosa Zanzari 《Geothermics》1988,17(4)
The hydrogeochemical study of the cold springs present in the Mt. Amiata geothermal area, where the Bagnore and Piancastagnaio geothermal fields are situated, has defined the different shallow groundwater systems.The cold groundwater temperature of the volcanic phreatic aquifer is largely correlated with the geothermal heat flow. Through the analysis of the temperature of cold groundwaters, a possible method for geothermal prospection has been developed, supported by the results obtained in the studied area. Through the enthalpic balance of the aquifer and in agreement with available data, a geothermal flow of about 200 mW m-2 has been calculated. 相似文献
95.
Maurizio Martino Anna Paola Caricato Francesco Romano Tiziana Tunno Daniele Valerini Marco Anni M. Elisabetta Caruso Alessandro Romano Tiziano Verri 《Journal of Materials Science: Materials in Electronics》2009,20(Z1):435-440
We report on the deposition of soft matter thin films by Matrix Assisted Pulsed Laser Evaporation (MAPLE). In particular,
thin layers of biological material (Bovine Serum Albumin) and polymers (polyfluorene) for medical and optoelectronic applications,
were realized by laser irradiating a frozen solution containing a low amount of material diluted in a laser absorbing volatile
solvent. The depositions were carried out varying different parameters as solvent–solute concentration, solvent nature, laser
fluencies, etc. The optical, morphological, structural and spectroscopical properties were detected by means of different
analyses as FTIR, photoluminescence, AFM and SDS. 相似文献
96.
97.
Carla D. Di Mattia Giampiero Sacchetti Dino Mastrocola Dipak K. Sarker Paola Pittia 《Food Hydrocolloids》2010,24(6-7):652-658
The surface and interfacial properties of gallic acid, catechin and quercetin, and their effect on the dispersion degree and the oxidative stability of olive oil oil-in-water (O/W) emulsions prepared using β-lactoglobulin and Tween 20 were studied.Gallic acid showed no effect on the surface properties while catechin was proven to be able to accumulate at the air/water interface, decreasing the surface tension values with increasing its concentration. All the phenolic antioxidants caused a decrease in the interfacial tension at the oil/water interface, even though only catechin and quercetin showed a concentration dependent behaviour.In emulsions, gallic acid did not affect the droplet size of the systems, catechin caused the formation of oil droplets bigger than those of the control, whilst quercetin improved the dispersion state of the emulsions with the increasing of its concentration. Gallic acid, despite its partitioning in the water phase due to its polarity, delayed the formation of both the hydroperoxides and TBARs and limited their accumulation. Catechin did not affect the formation of oxidation products whilst quercetin, among the tested antioxidants, caused the lowest formation of both hydroperoxides and TBARs through 33 days of storage. 相似文献
98.
Potentilla erecta (L.) is known for the high concentration of proanthocyanidin oligomers (PAs) in its underground parts. The use of its preparations as food supplements and the lack of chemical–analytical studies concerning with an efficient chromatographic separation procedure for these compounds led us to develop a strategy to profile PAs occurring in this species. 相似文献
99.
Francesca Mainini Alessandro Contini Donatella Nava Paola Antonia Corsetto Angela Maria Rizzo Elisabetta Agradi Elena Pini 《Journal of the American Oil Chemists' Society》2013,90(11):1751-1759
Quercetin shows interesting pharmacological effects, but its use in topical applications is limited by its low skin permeability and solubility. In this work, the synthesis of highly lipophilic quercetin esters with oleic, linoleic and linolenic acid useful as topical quercetin prodrugs is reported. Partial OH esterification is advisable to maintain the antioxidant activity of these compounds; tetraesters and triesters can be achieved by modulating the reaction conditions utilized for the total esterification of quercetin. The chemical structures of the esters were proven by spectroscopic techniques; quantum chemical NMR calculation were mandatory to unequivocally assign the free position in triesters. Finally, the antioxidant activity of all the synthesized compounds was determined by the 2,2-diphenyl-1-picryl-hydrazyl method and by 2,2-azinobis(3-ethyl-benzothiazoline-6-sulfonic acid) assay. 相似文献