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101.
D. Duracher F. Sauzedde A. Elaissari A. Perrin C. Pichot 《Colloid and polymer science》1998,276(3):219-231
Cationic hydrophilic copolymer latexes were synthesized at 70 °C either by batch or two-step emulsifier-free emulsion poly-merization
of styrene (St), N-iso-propylacrylamide (NIPAM), and aminoethylmethacrylate hydro-chloride (AEM) using 2,2′-azobis (2-amidinopropane) dihydrochloride
as initiator. At first, batch polymerization kinetics were followed by gas chromatography (GC), revealing that NIPAM rapidly
homopolymerized, before the polymerization of styrene had started. Particle size analysis by quasi-elastic light scattering
(QELS) and transmission electron microscopy (TEM) showed that monodispersed particles were obtained with the formation of
a poly[NIPAM] rich shell. Adding a small amount of the cationic monomer caused a strong decrease of the particle size without
affecting the size monodispersity. When a shot process was used, a narrow particle size distribution was maintained, provided
that the monomer addition was performed at a relatively high conversion of the first batch step. The poly[NIPAM] rich shell
layer was larger with the shot process, but increasing the amino-containing monomer in the recipe resulted in a dramatic decrease
of the thickness. Combination of transmission, scanning and atomic force microscopy techniques showed that these hydrophilic
particles exhibited odd-shaped structures, the unevenness being dependent upon the performed process. Kinetic data and particle
morphology information were inferred for discussion of the polymerization mechanism of this system.
Received: 21 August 1997 Accepted: 22 October 1997 相似文献
102.
This article examines the current status of Markov processes in single molecule fluorescence. For molecular dynamics to be described by a Markov process, the Markov process must include all states involved in the dynamics and the first-passage time (FPT) distributions out of those states must be describable by a simple exponential law. The observation of non-exponential FPT distributions or other evidence of non-Markovian dynamics is common in single molecule studies and offers an opportunity to expand the Markov model to include new dynamics or states that improve understanding of the system. 相似文献
103.
Ping He 《Journal of fluorine chemistry》2005,126(1):113-120
The reactions of fluoroalkanesulfonyl azides RfSO2N31 with N-alkylindoles 2 have been studied in detail. It was found that both solvent and the amount of the azides seriously affected the product distribution. 1 reacted with equimolar of 2 in ether or 1,4-dioxane affording 2-(N-substituted-indolinylidene)fluoroalkane sulfonylimines 3 as major product; While, treatment of 2 with 2 equiv. of 1 in ethanol, an unexpected product N-substituted-2-fluoroalkanesulfonimino-3-diazo-indolines 4 were obtained in good yield. The reaction mechanism was discussed. 相似文献
104.
105.
SYNTHESIS OF MESOPOROUS POLY(STYRENE-co-MALEIC ANHYDRIDE)/SILICA HYBRID MATERIALS VIA A NONSURFACTANT-TEMPLATED SOL-GEL PROCESS* 总被引:1,自引:0,他引:1
Jie-bin Pang Kun-yuan Qiu Yen Wei Department of Polymer Science Engineering College of Chemistry Molecular Engineering Peking University Beijing China. Department of Chemistry Drexel University Philadelphia Pennsylvania USA. 《高分子科学》2000,(5):469-472
Mesoporous poly (styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis wasachieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydride copolymerin the presence of 3-aminopropyl triethoxysilane (APTES) as a coupling agent and citric acid as a nonsurfactant template orpore-forming agent, followed by ethanol extraction. Characterization results from nitrogen sorption isotherms and powder X-ray diffraction indicate that polymer-modified mesoporous materials with large specific surface areas (e.g. 900 m~2/g) andpore volumes (e.g. 0.6 cm~3/g) could be prepared. As the citric acid concentration is increased, the specific surface areas, porevolumes and pore diameters of the hybrid materials increase. 相似文献
106.
In the light of the plate tectonics the outline of paleogeography, sedimentary properties and facies patterns in the depositional processes of the Wutong Formation at the Lower Yangtze area are discussed. The argument that the Wutong Formation contains not only terrestrial sediments but also marine-terrestrial transitional or marine sediments is expounded to cover the development, evolution and paleoclimate of the Wutong depositional regions. 相似文献
107.
Mikkelsen Ø Skogvold SM Schrøder KH Gjerde MI Aarhaug TA 《Analytical and bioanalytical chemistry》2003,377(2):322-326
Evaluation of different solid electrode systems for detection of zinc, lead, cobalt, and nickel in process water from metallurgical nickel industry with use of differential pulse stripping voltammetry has been performed. Zinc was detected by differential pulse anodic stripping voltammetry (DPASV) on a dental amalgam electrode as intermetallic Ni–Zn compound after dilution in ammonium buffer solution. The intermetallic compound was observed at –375 mV, and a linear response was found in the range 0.2–1.2 mg L–1 (r2=0.98) for 60 s deposition time. Simultaneous detection of nickel and cobalt in the low g L–1 range was successfully performed by use of adsorptive cathodic stripping voltammetry (AdCSV) of dimethylglyoxime complexes on a silver–bismuth alloy electrode, and a good correlation was found with corresponding AAS results (r2=0.999 for nickel and 0.965 for cobalt). Analyses of lead in the g L–1 range in nickel-plating solution were performed with good sensitivity and stability by DPASV, using a working electrode of silver together with a glassy carbon counter electrode in samples diluted 1:3 with distilled water and acidified with H2SO4 to pH 2. A new commercial automatic at-line system was tested, and the results were found to be in agreement with an older mercury drop system. The stability of the solid electrode systems was found to be from one to several days without any maintenance needed. 相似文献
108.
Synthesis of silanized polyether urethane hybrid systems. Study of the curing process through hydrogen bonding interactions 总被引:1,自引:0,他引:1
Different types of silanized polyurethanes (SPUR) were prepared in two ways: the first type (a), by reacting a polyether diol with an isocyanatesilane and the second type (b) by reacting it with diisocyanate (IPDI) and afterwards with aminosilane. These systems are able to cure with atmospheric moisture and, as a consequence, a tridimensional hybrid structure is formed where the inorganic and organic phases are bonded with covalent bonds. The evolution of the curing process in both systems has been monitored by means of Fourier transform infrared spectroscopy, through the changes observed in the carbonyl stretching vibration region. The results obtained show that the SPURs of kind (b) present stronger hydrogen bonding interactions as a consequence of urea groups present in the final structure. Moreover, given the proximity of both urethane and urea groups to alkoxysilane end groups, during the alkoxysilane curing process these groups are forced to approximate themselves even further and therefore the reticulation process leads to an increase of the self association of urethane and urea groups.Finally, DSC has been used to measure Tg values of the systems studied before and after the curing process. The obtained results have confirmed the main conclusions obtained in FTIR analysis. 相似文献
109.
P. Baltazar V. H. Lara G. Córdoba R. Arroyo 《Journal of Sol-Gel Science and Technology》2006,37(2):129-133
Samples of TiO2 doped with 2 and 5 mol% of Cu2+ were prepared by the sol-gel process. Titanium(IV) isopropoxide and copper(II) nitrate were used as precursors. The samples
were prepared as monolithic shapes, dried at 80°C for 72 h and heat treated at various temperatures in the range 200–900°C
for 2 h. The structural transformation and texture of the samples were investigated by X-ray powder diffraction (XRD) and
nitrogen adsorption. Significant changes were observed during the crystallization process; on the one hand, the crystallization
profiles show that crystallization occurs uniformly and is practically insensitive to the dopant concentration, but when the
transformation at a given temperature is followed as a function of time, the rate of the amorphous-anatase transformation
is larger for the sample containing 2 mol% Cu2+. Electron spin resonance (ESR) results show that in this sample there is no segregation of Cu2+ ions. The sample containing 2 mol% of Cu2+ was selected for the kinetic studies and the temperatures selected were 300, 325, 350, 375 and 400°C, which were taken from
the amorphous to anatase crystallization profile. An activation energy of 137 ± 4 kJ/mol for the crystallization process was
estimated from the kinetic data. These results showed that the effect of the open structure present in the TiO2 amorphous phase provides the atomic mobility required for the crystallization. On the other hand, the differences in the
crystallization rate due to the amount of Cu2+ were explained by the segregation of copper ions to the surface of the samples. 相似文献
110.
Bord N Crétier G Rocca JL Bailly C Souchez JP 《Analytical and bioanalytical chemistry》2004,380(2):325-332
Alkanolamines such as diethanolamine (DEA) and N-methyldiethanolamine (MDEA) are used in desulfurization processes in crude oil refineries. These compounds may be found in process waters following an accidental contamination. The analysis of alkanolamines in refinery process waters is very difficult due to the high ammonium concentration of the samples. This paper describes a method for the determination of DEA in high ammonium concentration refinery process waters by using capillary electrophoresis (CE) with indirect UV detection. The same method can be used for the determination of MDEA. Best results were achieved with a background electrolyte (BGE) comprising 10 mM histidine adjusted to pH 5.0 with acetic acid. The development of this electrolyte and the analytical performances are discussed. The quantification was performed by using internal standardization, by which triethanolamine (TEA) was used as internal standard. A matrix effect due to the high ammonium content has been highlighted and standard addition was therefore used. The developed method was characterized in terms of repeatability of migration times and corrected peak areas, linearity, and accuracy. Limits of detection (LODs) and quantification (LOQs) obtained were 0.2 and 0.7 ppm, respectively. The CE method was applied to the determination of DEA or MDEA in refinery process waters spiked with known amounts of analytes and it gave excellent results, since uncertainties obtained were 8 and 5%, respectively. 相似文献