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991.
Abstract The flexural strengths of N-vinylpyrrolidone modified glass-ionomer cements were investigated. The optimal molar ratio of the monomers in copolymers, composed of the three components acrylic acid, itaconic acid and N-vinylpyrrolidone, was determined using a SAS statistical program. The copolymers were prepared using a free-radical polymerization process. The viscosities of aqueous solutions of these polymers were determined. Cements were formed by the reaction of these solutions with glass particles. Flexural strength (FS) was used as the basic screening property to find the optimum molar ratio. Statistical models were applied to predict the optimum molar ratios. All strength values were recorded on the specimens conditioned in distilled water at 37°C for 7 days. The optimal molar ratio for these copolymers was 7:1:3 for poly(acrylic acid-co-itaconic acid-co-N-vinylpyrrolidone), based on flexural strength and viscosity. The effect of molecular weight (MW) on FS was also evaluated. Copolymer with a MW of 10, 800 (Mn) showed 85% higher FS than the Ketac-Molar (KM) system, along with a reasonable working viscosity. 相似文献
992.
Based on infrared absorption spectroscopy technique, a carbon monoxide sensor was developed using the fundamental absorption band of carbon monoxide molecule at the wavelength around 4.6 µm. The developed sensor consists of pulse-modulated wideband incandescence, open ellipsoid light-collector gas-cell, dual-channel detector, and control and signal-processing module. With the prepared standard carbon monoxide gas sample, sensing characteristics on carbon monoxide were investigated using the sensor. Experimental results reveal that the limit of detection is about 10 ppm, the relative error at the limit of detection point is less than 14%, and that is less than 7.8% within the low concentration range of 20~180 ppm. The maximum absolute errors of 50 min long-term measurement on the 0 and 14 ppm CO gas samples are about 3 and 3.17 ppm, respectively, and the standard deviations are as small as 0.18 and 1.25 ppm, respectively. Compared with the reported carbon monoxide detection systems utilizing quantum cascaded lasers and distributed feedback lasers, the proposed sensor shows potential applications in carbon monoxide detection under the circumstances of coal-mine and environmental protection, by virtue of high performance, low cost, simple optical structure, and so on. 相似文献
993.
A series of Mannich base derivatives of 2-hydroxy-chalcones were obtained expediently in good to excellent yields by microwave-assisted Mannich reaction. The regioselectivity of the reaction occurred preferentially at the C-3 position of the 2-hydroxy-chalcone backbone. In comparison with conventional results, results from microwave possesses give better yields in shorter times. Further vasorelaxation assay showed that 2-hydroxy-3-((4-methylpiperazin-1-yl)methyl)-4,6-dimethoxymethoxy-3′-bromo-chalcone 8 significantly decreased maximal PE-induced contraction (Emax = 100 ± 5.97%, EC50 = 10.2 ± 0.51 µM). 相似文献
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Wentong Gao Jianwei Xu Pengfei Zuo Hao Dong Yiwu Quan Pengshan Chang 《Journal of polymer science. Part A, Polymer chemistry》2019,57(13):1460-1466
The dynamic chemistry of disulfide bonds has emerged as one of the most powerful tools used for the fabrication of organic compounds and self‐healing materials. In this article, a novel aromatic amine‐terminated polysulfide oligomer is first synthesized from thiol‐terminated polysulfide oligomer and bis(4‐aminophenyl) disulfide via disulfide metathesis mechanism. The resulting oligomer is confirmed by FTIR and 1H NMR spectra and then successfully applied in constructing self‐healable polyurea material (A‐LP23‐I), which combines the advantages of higher strength of polyureas and excellent self‐healing ability of polysulfide‐based materials. After subjecting to a temperature of 75 °C for 48 h, both the tensile strength and ultimate elongation of A‐LP23‐I restore to more than 90% of the original values (3.32 MPa and 396%). This study demonstrates a novel strategy for synthesizing aromatic amine‐terminated oligomer. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1460–1466 相似文献
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Junghoon Cha Sughwan Kim Kyung-Won Park Dong Ryeol Lee Jae-Hun Jo Sumin Kim 《Journal of Thermal Analysis and Calorimetry》2014,116(1):219-224
In buildings, windows have a major influence on space heating demand and indoor environment both with respect to climate and daylight. To reduce the window coefficient of the overall heat transmission, we use aerogel. Aerogels have a high surface area, low density, open pore structure, and excellent insulation properties. We mixed pressure sensitive adhesive and aerogel (10, 15, and 20 mass%) using a homogenizer. A mixture of the adhesives and silica aerogels attached film can reduce thermal conductivity. Silica aerogels are characterized by a surface area analyzer (BET), a Fourier transform infrared spectrometer, a thermogravimetry (TG) analyzer, and probe tack method. Thermal conductivity was measured by a TCi thermal conductivity analyzer. 相似文献