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61.
The free‐radical graft polymerization of vinyl acetate onto nonporous silica particles was studied experimentally. The grafting procedure consisted of surface activation with vinyltrimethoxysilane, followed by free‐radical graft polymerization of vinyl acetate in ethyl acetate with 2,2′‐azobis(2,4‐dimethylpentanenitrile) initiator. Initial monomer concentration was varied from 10 to 40% by volume and the reaction was spanned from 50 to 70°C. The resulting grafted polymer, which was stable over a wide range of pH levels, consisted of polymer chains that are terminally and covalently bonded to the silica substrate. The experimental polymerization rate order, with respect to monomer concentration, ranged from 1.61 to 2.00, consistent with the kinetic order for the high polymerization regime. The corresponding rate order for polymer grafting varied from 1.24 to 1.43. The polymer graft yield increased with both initial monomer concentration and reaction temperature, and the polymer‐grafted surface became more hydrophobic with increasing polymer graft yield. The present study suggests that a denser grafted polymer phase of shorter chains was created upon increasing temperature. On the other hand, both polymer chain length and polymer graft density increased with initial monomer concentration. Atomic force microscopy–determined topology of the polymer‐grafted surface revealed a distribution of surface clusters and surface elevations consistent with the expected broad molecular‐weight distribution for free‐radical polymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 300–310, 2003 相似文献
62.
Lida T Nakamori R Yabuta R Yada S Takagi Y Mano N Ikegawa S Goto J Nambara T 《Lipids》2002,37(1):101-110
A facile and efficient synthesis of the carboxyl-linked glucosides of bile acids is described. Direct esterification of unprotected
bile acids with 2,3,4,6-tetra-O-benzyl-d-glucopyranose in pyridine in the presence of 2-chloro-1,3,5-trinitrobenzene as a coupling agent afforded a mixture of the
α- and β-anomers (ca. 1∶3) of the 1-O-acyl-d-glucoside benzyl ethers of bile acids, which was separated effectively on a C18 reversedphase chromatography column (isolated yields of α- and β-anomers are 4–9% and 12–19%, respectively). Subsequent hydrogenolysis
of the α- and β-acyl glucoside benzyl ethers on a 10% Pd−C catalyst in acetic acid/methanol/EtOAc (1∶2∶2, by vol) at 35°C
under atmospheric pressure gave the corresponding free esters in good yields (79–89%). Chemical specificities such as facile
hydrolysis and transesterification of the acyl glucosides in various solvents were also discussed. 相似文献
63.
Jinhua Chen Upita Septiani Masaharu Asano Yasunari Maekawa Hitoshi Kubota Masaru Yoshida 《应用聚合物科学杂志》2007,103(3):1966-1972
In this study the fluoropolymers, poly(ethylene‐co‐tetrafluoroethylene) (ETFE) and poly(vinylidene fluoride) (PVDF) films, together with the radiation‐induced crosslinked polytetrafluoroethylene (cPTFE) film were compared on the basis of their preparation and properties of radiation‐grafted polymer electrolyte membranes. The polymer electrolyte membranes were prepared by radiation grafting of styrene into the base films and subsequent sulfonation. The proton conductivity and chemical stability of the three types of membranes with a similar ion exchange capacity (IEC) near 1.0 mmol/g were investigated and are discussed in detail. Although the ETFE‐based polymer electrolyte membrane was relatively more stable, its proton conductivity was lower than those of the PVDF‐ and cPTFE‐based membranes. On the other hand, the cPTFE‐based membrane showed a significantly higher proton conductivity, but its chemical stability was shorter than that of the ETFE‐based membrane. It is considered that the difference in the preparation and properties of the polymer electrolyte membranes was due to the difference in the degree of crystallinity as well as in the chemical structure of the fluoropolymer base films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1966–1972, 2007 相似文献
64.
This study concerns a comparative study of three crosslinkers, divinylbenzene (DVB), 1,2‐bis(p,p‐vinylphenyl)ethane (BVPE), and triallyl cyanurate (TAC) crosslinked poly(ethylene‐co‐tetrafluoroethylene) (ETFE)‐based radiation‐grafted membranes, which were prepared by radiation grafting of p‐methylstyrene onto ETFE films and subsequent sulfonation. The effect of the different types and contents of the crosslinkers on the grafting and sulfonation, and the properties such as water uptake, proton conductivity, and thermal/chemical stability of the resulting polymer electrolyte membranes were investigated in detail. Introducing crosslink structure into the radiation‐grafted membranes leads to a decrease in proton conductivity due to the decrease in water uptake. The thermal stability of the crosslinked radiation‐grafted membranes is also somewhat lower than that of the noncrosslinked one. However, the crosslinked radiation‐grafted membranes show significantly higher chemical stability characterized in the 3% H2O2 at 50°C. Among the three crosslinkers, the DVB shows a most pronounced efficiency on the crosslinking of the radiation‐grafted membranes, while the TAC has no significant influence; the BVPE is a mild and effective crosslinker, showing the moderate influence between the DVB and TAC crosslinkers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4565–4574, 2006 相似文献
65.
Tatsuya Kodama Ken-ichi Tominaga Masahiro Tabata Takashi Yoshida Yutaka Tamaura 《Journal of the American Ceramic Society》1992,75(5):1287-1289
Active wustite (FeδO, with a δ value of 0.98) was prepared by keeping normal wustite (δ value of 0.94) in a N2 atmosphere at 300°C for 10 min. This reaction is given by (4δ2 –3)Feδ1 O→(4δ1 –3)Feδ2 O + (δ2 –δ1 )Fe3 O4 where δ1 = 0.94 and δ2 = 0.98. The equation indicates that the normal wustite undergoes eutectoid decomposition into active wustite and stoichiometric magnetite (Fe3 O4 ). Carbon dioxide (1.013 × 105 Pa) was almost completely (100%) decomposed into carbon (zero valence) by the active wustite at the low temperature of 300°C, which was associated with the transformation of the active wustite into the stoichiometric magnetite. The internal pressure of the reaction cell eventually became a vacuum. 相似文献
66.
Satoru Sano Noriko Saito Shin-ichi Matsuda Naoki Ohashi Hajime Haneda You Arita Minoru Takemoto 《Journal of the American Ceramic Society》2006,89(2):568-574
Forsterite (Mg2 SiO4 ) ceramics were prepared using Mg(OH)2 and SiO2 as precursors, and the effect of powder characteristics of Mg(OH)2 on calcination and sintering was investigated. The use of highly dispersed Mg(OH)2 powder (HD powder) resulted in a lower calcination temperature. Forsterite powder of high homogeneity and small particle size prepared from the HD powder enabled synthesis of high-density forsterite ceramics by ordinary sintering without applying external pressure. Moreover, transparent forsterite ceramics were successfully synthesized through addition of excess Mg to the precursors to compensate for Mg evaporated during the sintering process. Subsequent dielectric measurements revealed that the transparent forsterite ceramics had a very low dielectric loss (tan δ<10−4 ). 相似文献
67.
Summary Segmented polymers with random sequences of conjugated and non-conjugated blocks are produced by partial dehydrogenation of poly(-thiophenediyl)benzylidene. The fraction of conjugated block was controlled by the elimination time. The polymers gave photoluminescence. Absorption coefficients of the polymers increased with the rate of dehydrogenation, and the highest fluorescence intensity were achieved around 9 % conjugation conversion. The polymers were characterized by 1H- and 13C-n.m.r. and infrared spectra, and were soluble in common organic solvents, which suggests a good processability. 相似文献
68.
Sohei Sato Hironori Hondoh Satoru Ueno 《Journal of the American Oil Chemists' Society》2021,98(3):269-280
Fat bloom in chocolate is a substantial problem that affects its sensory properties, such as texture and appearance. This phenomenon is because of diffuse light reflection on a roughened surface of chocolate, caused by structural changes of fat crystals subjected to various temperature conditions. The purpose of this study is to characterize the fat bloom formed through gradual two-step cooling after exposure to temperatures (35–37 °C) slightly above the cocoa butter Form βV melting point (33.8 °C). To clarify the fat bloom formation process, the structural changes in cocoa butter and on the chocolate surface, at the dynamic thermal condition for bloom formation, was investigated using X-ray diffraction (XRD), fluorescence light microscopy, and scanning electron microscopy (SEM). The results revealed that an entirely light brown fat bloom occurred, even in the absence of the Form βVI or other polymorphic transformation. Microscopic observation showed that the light brown appearance was because of the porous structure on the chocolate surface. This porous structure was formed by liquid oil moving inside of chocolate from the surface. The formation of a coarse network and the subsequent de-oiling, because of movement of unsolidified liquid fat into the chocolate, appeared to be the main causes of bloom formation. Therefore, a coarsened fat network and oil movement besides the conventional principles of polymorphic transformation of cocoa butter should be considered. 相似文献
69.
碳基钨涂层在退火过程中的组织和结构变化 总被引:2,自引:0,他引:2
用真空等离子体喷涂(VPS)技术在C/C复合材料基体上制备了厚度为0.5mm的钨(W)涂层,涂层的表面通过物理气相沉积(PVD)预沉积钨、铼(Re)多层作为碳(C)的扩散势垒。涂层经过1200℃--2000℃的电子束退火,其微观结构和化学构成发生变化。经测量涂层的再结晶温度约为1400℃,再结晶的活性能为63kJ/mol。当退火温度高于1300℃时,涂层表面的多层W、Re结构将由于W、Re和C之间的相互扩散而发生改变,并在1600℃以上退火lh后由于脆性碳化钨在界面的形成而完全失效,碳化钨层的厚度将随着退火漏度的升高和退火时间的延长而迅速增加。 相似文献
70.
Kazunori Nagasaka Takeshi Yoshida Yoshihiro Kita Fumio Hashimoto 《International Journal of Machine Tools and Manufacture》1987,27(2)
For optimization of abrasive cut-off operation, wheel wear equation must be identified before the operation is optimized. The equation is obtained by using GMDH algorithm with successive determination of trends containing interactive terms. In the model equation factors of grinding fluid are taken into consideration in addition to the factors of wheel, work material, feed (table speed) and wheel speed. For the identification of the model wheel wear tests are performed under the experimental design treating the above-mentioned factors as independent variables. The grinding ratio (output in the model) can be predicted for combinations of various factors using the model. With the wheel wear equation and machining cost model, the optimum combination of wheel, fluid, feed and wheel speed can be selected for a given work material. The relationships between these variables and the costs are investigated. 相似文献