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481.
Atsushi Asano Masaru Eguchi Takuzo Kurotu 《Journal of Polymer Science.Polymer Physics》1999,37(16):2007-2012
Thermal dehydration process of PMAA was investigated by solid‐state 13C NMR. For heat‐treated PMAA at 150°C, at which the dehydration goes very slowly, we observed three 13C peaks at 172, 178, and 187 ppm in the carboxyl group region. The peak at 172 ppm is due to the intramolecular cyclic anhydrides by comparing the reported value of 13C chemical shift. The peaks at 178 and 187 ppm were assigned to regularly aligned free carboxylic acids and intermolecular acid dimers, respectively, from the 2D‐exchange 13C NMR spectra, 13C chemical shift values and IR spectra. We concluded that by heat‐treatment the rearrangement of intermolecular hydrogen bonding of the carboxylic acids in PMAA occurs firstly to form the regularly aligned acid dimers, and the dimers dissociated to be the regularly aligned free carboxylic acids at high temperatures. The adjacent free carboxyl acids dehydrate with each other, resulting in the formation of intramolecular anhydrides. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2007–2012, 1999 相似文献
482.
采用市售廉价大孔α-Al2O3管作为基质材料,通过热浸渍法在管外表面涂敷晶种,随后在无模板剂体系下,利用新型的间歇式水热合成法制备丝光沸石膜。对比了传统加热和间歇式加热对丝光沸石膜形貌、结构及渗透蒸发异丙醇脱水分离性能的差异。考察了合成液中Na2O/SiO2、SiO2/Al2O3和NaF/SiO2物质的量之比在间歇式水热合成下对丝光沸石膜的影响。研究结果表明,当合成液中Na2O/SiO2、SiO2/Al2O3和NaF/SiO2物质的量之比分别为0.24、16.7和0.25时,制备的丝光沸石膜渗透蒸发异丙醇脱水分离性能最佳,在75℃下,对异丙醇/水(9:1,w/w)的渗透通量达5.60 kg·m-2·h-1,水对异丙醇的分离因数大于10 00... 相似文献
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Variable temperature diffuse reflectance infrared spectroscopy is used to monitor the dehydration of sodium Linde type A zeolite (NaA). Between ambient temperature and 423 K, water desorbs from NaA α-cages. At 423 K, remaining NaA water molecules are primarily confined to β-cages. Variable temperature infrared difference spectra band shape and intensity trends reflect the influence of water-Na+ interactions and hydrogen bonding on α-cage water desorption mechanisms. Difference spectrum variations suggest that water loss is accompanied by rearrangement of the remaining NaA water molecules to establish new interactions and minimize potential energies. Water molecules that do not interact with Na+ form multiple water-water hydrogen bonds and attain near bulk water configurations. These waters desorb at the lowest temperatures. Most α-cage waters are involved in Na+ interactions. These water molecules participate in hydrogen bonding with neighboring water molecules, but opportunities diminish with increased dehydration, resulting in systematic temperature-dependent vibrational spectrum changes. 相似文献
486.
《Mendeleev Communications》2023,33(4):479-480
A simple and facile synthesis of racemic 15-deoxy-Δ12,14-prostaglandin J2 methyl ester from readily available Corey lactone diol in total eleven steps was suggested. The standard methods provided a pathway to a block with an integrated w w w-chain and further to PGJ2 methyl ester. The latter was smoothly converted to the target prostaglandin in the TsOH–CH2Cl2 medium when allylic alcohol moiety was transformed to exocyclic diene substituent conjugated with endocyclic enone system. 相似文献
487.