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121.
Kenji Miyatake Tomohiro Yasuda Masahiro Watanabe 《Journal of polymer science. Part A, Polymer chemistry》2008,46(13):4469-4478
A series of sulfonated polyimide (SPI) copolymers containing methyl, methoxy, or fluorine groups were synthesized to elucidate the substituents effect on their proton conducting properties as well as thermal, hydrolytic, and oxidative stability for polymer electrolyte membrane fuel cell applications. SPIs of high molecular weight (Mw > 200 kDa, Mn > 80 kDa) along with the ion exchange capacity (IEC) varying between 1.34 and 1.91 mequiv/g were obtained, which gave tough, ductile, and flexible membranes by solution casting. The thermal properties of the SPIs were dominated by the electronic structure of the sulfonated aromatic rings. The electron‐donating methyl groups lowered the thermal decomposition temperature. The hydrolytic and oxidative stability was roughly in the order of IEC (the higher IEC membranes were less stable). Fluorine groups, either as ? F or ? CF3, had negative effect on the hydrolytic and oxidative stability. In the water uptake and proton conductivity, hydrophobic components are rather more influential than the substituents. It was found out that the SPI(5, 8, 0.7) containing bis(phenoxy)biphenylene sulfone moieties as a rigid hydrophobic component showed the best balanced properties in terms of the stability and the proton conductivity for its rather low IEC. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4469–4478, 2008 相似文献
122.
A macrocyclic host molecule that comprised two different rotating modules, cerium(IV) bis(porphyrinate)s and ferrocenyl rotating units, exhibiting contraction/expansion motion was synthesized, which can be regarded as a prototype of artificial molecular spring driven by cooperative guest binding in 1:6 stoichiometry. 相似文献
123.
124.
Tomohiro Narukawa Takayoshi Kuroiwa Izumi Narushima Koichi Chiba 《Analytical sciences》2008,24(3):355-360
The sensitivity of graphite furnace atomic absorption spectrometry (GFAAS) to arsenobetaine (AB) was 1.3-times higher than to inorganic As. In order to understand the mechanism underlying this observation, the atomization processes for both chemical species were investigated in terms of the enthalpy change (DeltaH) during the atomization process in GFAAS. The enthalpy change of AB was slightly lower than that of inorganic As, which suggested that AB was atomized more efficiently than was inorganic As. Moreover, it was observed that some co-existing organic materials enhanced the analytical sensitivity of inorganic As. The sensitivity difference between inorganic As and AB depended upon the mechanisms of their atomization processes. 相似文献
125.
126.
Enantioselective hydrogenation of methyl 4-(4-biphenylyl)-3-oxobutanoate over a tartaric acid-modified Raney nickel catalyst gave the title compound in 82% ee, which was enantiomerically enriched by recrystallizations. The product was converted to an (R)-3-acetoxyglutaric acid half ester via a ruthenium-catalyzed oxidation. 相似文献
127.
-Ni(H2O)6 · SO4 and its selenate derivative exhibit chirality only in the solid-state. We have observed, for the first time, a sign inversion of CD (circular dichroism) in the 3A2g → 3T1g(P) Ni(II) d–d transition at near liquid nitrogen temperatures. The novel finding was achieved by building a new cooling unit to a solid-state specialized Universal Chiroptical Spectrophotometer (UCS-1) [R. Kuroda, T. Harada, Y. Shindo, Rev. Sci. Instrum. 72 (2001) 3802.] and by formulating an analytical procedure to obtain artifact-free CD signals based on the Mueller matrix method. The sign inversion is remarkable as the crystal structure hardly changes from 300 to 100 K. The origin of the sign inversion is discussed. 相似文献
128.
Chizuko Kabuto Yutaka Higuchi Tomohiro Niimi Fumio Hamada Nobuhiko Iki Naoya Morohashi Sotaro Miyano 《Journal of inclusion phenomena and macrocyclic chemistry》2002,42(1-2):89-98
X-Ray crystal structures of the mono-, di-, and tri(p-tert-butyl)-substituted thiacalix[4]arenes (TC4As; 1, 2, and 3, respectively) have beendetermined. TC4As 1–3 adopt a cone conformation and form dimeric self-inclusion units in such a manner that phenol moieties are inserted into the cavity of each molecule. In all the crystal structures of 1–3, lateralface-to-face interactions exist between the phenol rings that do not bear a tert-butyl substituent, and seemingly, this molecular assembly stabilizes the formation of self-inclusion. TC4As 1 and 2 adopt a cone conformation with C2 symmetry, leading to the formation of rim-to-rim intermolecular hydrogenbonds so as to link the dimeric units up and down. On the other hand, 3 adopts a regular cone conformation with C4 symmetry to form cyclic hydrogen bonds withinthe rim part of TC4A. 相似文献
129.
We consider the totally asymmetric simple exclusion process, a model in the KPZ universality class. We focus on the fluctuations of particle positions, starting with certain deterministic initial conditions. For large time t, one has regions with constant and linearly decreasing density. The fluctuations on these two regions are given by the Airy1 and Airy2 processes, whose one‐point distributions are the GOE and GUE Tracy‐Widom distributions of random matrix theory. In this paper we analyze the transition region between these two regimes and obtain the transition process. Its one‐point distribution is a new interpolation between GOE and GUE edge distributions. © 2007 Wiley Periodicals, Inc. 相似文献
130.
Tomohiro Hirano Shuhei Masuda Shou Nasu Koichi Ute Tsuneyuki Sato 《Journal of polymer science. Part A, Polymer chemistry》2009,47(4):1192-1203
Radical polymerization of N,N‐dimethylacrylamide (DMAAm) was investigated in the presence of tartrates, such as diethyl L ‐tartrate, diisopropyl L ‐tartrate, and di‐n‐butyl L ‐tartrate, in toluene at low temperatures. Syndiotactic polymers were obtained in the presence of tartrates, whereas isotactic polymers were obtained in the absence of tartrates. The syndiotactic‐specificity increased with increasing amount of tartrates and with decreasing polymerization temperature. NMR analysis suggested that DMAAm and tartrates formed a 1:1 complex through double hydrogen bonding. A mechanism for the syndiotactic‐specific radical polymerization of DMAAm is proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1192–1203, 2009 相似文献