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Pradip K. Bhowmik Gregory Beaucage Subrata K. Bhattacharya Robert W. Lenz 《Journal of Polymer Science.Polymer Physics》1994,32(6):1023-1031
The degree of crystallinity of as-made fully aromatic, thermotropic polyesters was determined for two different series of polymers, each of which contained a symmetric monomer having either pendant phenyl groups or fused aromatic rings by the WAXD technique. All of the homopolymers had a high degree of crystallinity in spite of bulky substituents attached to the mesogenic moiety. Surprisingly, the homopolymer of 2,6-naphthalenedicarboxylic acid with each of the monomers had a higher degree of crystallinity and Tm than those of the homopolymer of terephthalic acid with each of the respective monomers. As expected, on copolymerization with 30 mol % of either 4-hydroxybenzoic acid or 6-hydroxy-2-naphthoic acid, all of the resulting copolymers had a much lower degree of crystallinity and Tm/Tf values compared to those of the respective homopolymers in each series. © 1994 John Wiley & Sons, Inc. 相似文献
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3,3',4,4'-Biphenyltetracarboxylic dianhydride (BPDA) was investigated as the central core unit in mesogenic molecules. Of particular interest was whether the BPDA unit could be self-constrained into a trans-conformation, and thus organize into a liquid crystalline phase. Two homologous series of symmetrical substituted model compounds, 3,3',4,4'-biphenyltetracarboxy-N-N'-bis-(4-n- alkylphenyl) diimides and 3,3',4,4'-biphenyltetracarboxy-N-N'-bis-(4-n- alkoxyphenyl)diimides were synthesized. For both series high temperature smectic A phases were observed. To our knowledge these are the first examples of liquid crystalline behaviour observed with BPDA as the mesogenic core. 相似文献
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Zusammenfassung Die Optimalbedingungen für die spektrophotometrische Bestimmung der L-Askorbinsäure mit TNBT wurden ermittelt. Die L-As-korbinsäure wurde in Anwesenheit eines 100fachen Überschusses folgender Stoffe bestimmt: Glukose, Fruktose, Saccharose, Wein-, Zitronen-, Oxal-, Äpfel- und Bernsteinsäure. 0,5g/ml ist die minimale Askorbinsäurekonzentration, die sich bestimmen läßt. Die rel. Standardabweichung beträgt 2,1%, der rel. Fehler 0,875%.
Spectrophotometric assay of L. ascorbic acid with 2,2,5,5-tetra-(4-nitro-phenyl)-3, 3-(3,3-dimethoxy-4,4-biphenyl)-ditetrazolium chloride (TNBT)
Summary The optimal conditions for spectrophotometric assay of L-ascorbic acid with TNBT were determined. L-ascorbic acid was assayed in the presence of a 100 fold excess of the following substances: glucose, fructose, sucrose, tartaric acid, citric acid, oxalic acid, malic acid and succinic acid. 0.5g/ml is the minimum concentration of ascorbic acid which can be assayed. The relative standard deviation is 2.1%, the relative error 0.875%.相似文献
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The synthesis and liquid crystal properties of eight members of the homologous series of 1-(4'-n-alkoxy-2,2',3,3',5,5',6,6'-octafluorobiphenyl-4-yl)-2-(trans-4-n-pentylcyclohexyl)-ethanes and eight members of the corresponding -ethanes, which have the E-configuration, are reported. These compounds are nematic, the ethenes having a considerably mesophase higher thermal stability than the analogous ethanes. 相似文献