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91.
Jessica E. Coughlin Andreas Reisch Marie Z. Markarian Joseph B. Schlenoff 《Journal of polymer science. Part A, Polymer chemistry》2013,51(11):2416-2424
Sulfonation of narrow polydispersity polystyrene, PS, standards remains the method of choice for generating polystyrene sulfonate, PSS, samples with defined composition. Although a variety of sulfonation techniques have been described, relatively little is reported on the material obtained, which is used for so many studies on the fundamental behavior of polyelectrolytes. Here, we show that powdered polystyrene treated with concentrated sulfuric acid (96%) at 90 °C without catalyst yields fully sulfonated PSS. Extensive characterization with 1H and 13C NMR as well as size exclusion chromatography coupled with static and dynamic light scattering shows no evidence of sulfone crosslinking or chain degradation under the conditions used. Though mono‐sulfonated as soon as it dissolves in the acid, the PSS contains about 6% meta substitution. Sulfonation kinetics for this heterogeneous reaction depend strongly on particle size, sulfuric acid content and temperature. For preparing perdeuterated PSS from the corresponding PS it is essential to employ D2SO4, as about half of the aromatic units undergo H/D exchange during sulfonation. The remaining ortho H/D may be exchanged with extended exposure to the concentrated sulfuric acid, but the meta site is deactivated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2416–2624 相似文献
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In the Fall of 1999, Illinois State University (ISU) piloted a new General Chemistry I course. This course now includes cooperative learning exercises that were developed and implemented in biweekly discussion sections over the past four semesters. We now have discussion exercises all taught by six different tenured and tenure-track faculty members. This study focuses on the effect on student behaviors and learning in General Chemistry I. Data were obtained from student surveys, student interviews, instructor feedback, and examination results. The results obtained in this study show that student interest in chemistry can be maintained or increased by the incorporation of cooperative learning into the general chemistry curriculum. In addition, this cooperative learning approach promoted attendance, was enjoyable for many students, and seemed to have some positive effect on achievement. 相似文献
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Ultrasound‐assisted emulsification microextraction coupled with high‐performance liquid chromatography for the simultaneous determination of fragrance allergens in cosmetics and water 下载免费PDF全文
Jessica Pérez‐Outeiral Esmeralda Millán Rosa Garcia‐Arrona 《Journal of separation science》2015,38(9):1561-1569
A simple, inexpensive, and environmentally friendly method based on ultrasound‐assisted emulsification microextraction followed by solidification of floating organic drop and high‐performance liquid chromatography coupled to diode array detection was developed for the simultaneous determination of 18 potentially allergenic fragrance substances. Several parameters affecting the microextraction process were investigated in detail by the “one‐variable‐at‐a‐time” approach. Optimal conditions were the following: 50 μL of 2‐dodecanol as extraction solvent, 10 mL of sample containing 150 g/L of salt, and 5 min of sonication at 35°C. Under the optimized conditions, method showed good linearity in the selected ranges, with squared correlation coefficients ranging from 0.948 to 0.999. Limits of detection ranged from 0.001 to 0.154 μg/mL and enrichment factors from 9 to 237. Precision of the method, expressed as relative standard deviation, was checked at two levels obtaining good results (3.3–14.4%). Recovery studies were made in baby bath water and in eau de cologne showing acceptable accuracy. Finally, the developed method was successfully applied to different commercial cosmetic and water samples. The most commonly found analyte was linalool followed by cinnamal and lilial. Most of the analyzed samples contained at least one of the target compounds. 相似文献
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Jessica Orrego Hernandez Jaime Portilla Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(5):363-368
Cyclohexylamine reacts with 5‐chloro‐3‐methyl‐1‐(pyridin‐2‐yl)‐1H‐pyrazole‐4‐carbaldehyde to give 5‐cyclohexylamino‐3‐methyl‐1‐(pyridin‐2‐yl)‐1H‐pyrazole‐4‐carbaldehyde, C16H20N4O, (I), formed by nucleophilic substitution, but with 5‐chloro‐3‐methyl‐1‐phenyl‐1H‐pyrazole‐4‐carbaldehyde the product is (Z)‐4‐[(cyclohexylamino)methylidene]‐3‐methyl‐1‐phenyl‐1H‐pyrazol‐5(4H)‐one, C17H21N3O, (II), formed by condensation followed by hydrolysis. Compound (II) crystallizes with Z′ = 2, and in one of the two independent molecular types the cyclohexylamine unit is disordered over two sets of atomic sites having occupancies of 0.65 (3) and 0.35 (3). The vinylogous amide portion in each compound shows evidence of electronic polarization, such that in each the O atom carries a partial negative charge and the N atom of the cyclohexylamine portion carries a partial positive charge. The molecules of (I) contain an intramolecular N—H...N hydrogen bond, and they are linked by C—H...O hydrogen bonds to form sheets. Each of the two independent molecules of (II) contains an intramolecular N—H...O hydrogen bond and each molecular type forms a centrosymmetric dimer containing one R22(4) ring and two inversion‐related S(6) rings. 相似文献
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Ying Zhang Yong-Guang Gao You-Di Shi Lian-Qian Tan Jessica S. Yue Zhong-Lin Lu 《中国化学快报》2015,26(7):894-898
A novel [12]aneN3-based BODIPY sensor 1 can be applied in the sequential recognition of Cu2 and ADP in aqueous solution and living cells with high selectivity and sensitivity 相似文献