共查询到20条相似文献,搜索用时 15 毫秒
1.
Vladislav V. Lopatin Andrei A. Askadskii Alexander S. Peregudov Viktor G. Vasil'ev 《应用聚合物科学杂志》2005,96(4):1043-1058
By IR and NMR spectroscopy methods, thermomechanical analysis, mechanical relaxation measurements, and computational simulation the effect of production conditions of acrylamide copolymer and N,N′‐methylenebisacrylamide derived hydrogels with respect to their properties were studied. Four hydrogel samples, prepared under different production conditions (γ‐radiation dose and autoclaving), were investigated. It was found that autoclaving and γ‐radiation lead to a slight increase of the crosslinking degree in the polymeric network and formation of alkene structures in polymeric chains. Stress relaxation and creep processes under axial compression of gel cylindrical samples were studied in detail. To approximate stress relaxation and creep curves new memory functions were used, based on the analysis of entropy production in the system during the relaxation process. It was found that primary γ‐radiation of initial gels induces an increase of quasi‐equilibrium rubbery elasticity modulus, and quasi‐equilibrium compliance is decreased. The opposite situation is observed during further autoclaving at 120°C. After autoclaving, required to sterilize the gels, their treatment by γ‐radiation again induced a noticeable increase of the modulus and compliance decrease. The mechanism of relaxation processes was found to be associated with the limiting stage of physical interaction between relaxants, representing different micro‐inhomogeneities in the material. The investigation results were compared with the data obtained by histology and morphology methods. A hydrogel obtained under additional γ‐radiation treatment and autoclaving did not swell when implanted into a living organism, and the tissue reaction to implantation of such gel was minimal. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1043–1058, 2005 相似文献
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Gaetano Giammona Gennara Cavallaro Giovanna Pitarresi Elisa Pedone 《Polymer International》2000,49(1):93-98
In the present study the derivatization of two water‐soluble synthetic polymers, α,β‐poly(N‐2‐hydroxyethyl)‐DL ‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy), with glycidyltrimethylammonium chloride (GTA) is described. This reaction permits the introduction of positive charges in the macromolecular chains of PHEA and PAHy in order to make easier the electrostatic interaction with DNA. Different parameters affect the reaction of derivatization, such as GTA concentration and reaction time. PHEA reacts partially and slowly with GTA; on the contrary the reaction of PAHy with GTA is more rapid and extensive. The derivatization of PHEA and PAHy with GTA is a convenient method to introduce positive groups in their chains and it permits the preparation of interpolyelectrolyte complexes with DNA. © 2000 Society of Chemical Industry 相似文献
4.
Particle dynamics and relaxation in bimodal suspensions during drying using multispeckle diffusing wave spectroscopy 下载免费PDF全文
Ki Wan Bong Hyun Wook Jung Seong Jae Lee 《American Institute of Chemical Engineers》2017,63(3):1114-1121
The motion of polystyrene particles in a bimodal suspension drop during drying was characterized via multispeckle diffusing wave spectroscopy. The fast and slow dynamics of bimodal particles, which were expressed in terms of autocorrelation function data from two kinds of cameras, were well connected in short and long lag time regimes. Characteristic time of β‐relaxation, representing the rapid movement of bimodal particles, became lower in the short lag time region as the portion of small particles increased, reflecting their fast Brownian motion. The difference in the relaxation features between bimodal suspension with large and small particles and unimodal suspension with only large particles became more evident as the size ratio between particles was high. Drying temperature could encourage the particle movement at the early stages of drying, leading to lower relaxation time, and inversely retard the relaxation behavior when drying time further elapsed, due to the structural rearrangement of particles. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1114–1121, 2017 相似文献
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Yohan Park Young Ju Lee Suckchang Hong Mi‐hyun Kim Myungmo Lee Taek‐Soo Kim Jae Kyun Lee Sang‐sup Jew Hyeung‐geun Park 《Advanced Synthesis \u0026amp; Catalysis》2011,353(18):3313-3318
A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers. 相似文献
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Tianbao Cheng Daining Fang Yazheng Yang 《Journal of the American Ceramic Society》2017,100(4):1598-1605
Knowledge of the surface energy of ceramic single crystals at elevated temperatures is of fundamental importance. However, it is very hard to obtain this quantity from the existing experiments, simulations, and theories. In the present work, following the Orowan‐Polanyi and Gilman models’ principles, two theoretical models for the temperature‐dependent surface energy of the ceramic single crystals are proposed based on the authors’ previous studies on the temperature‐dependent ideal tensile strength of solids. Thus established models relate the temperature dependence of the surface energy to these of the specific heat at constant pressure, Young's modulus, and coefficient of the linear thermal expansion. The temperature‐dependent surface energies of α‐Al2O3 and β‐Si3N4 are calculated and agree well with the experimental data. The study shows that the surface energy firstly remains approximately constant and then decreases linearly as temperature increases from 0 K to melting point. However, it has stronger temperature dependence than Young's modulus, that is, surface energy decreases more rapidly with increasing temperature. 相似文献
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Xiang Li Siyu Li Suyan Sun Fan Yang Weiguo Zhu Yu Zhu Yusheng Wu Yangjie Wu 《Advanced Synthesis \u0026amp; Catalysis》2016,358(10):1699-1704
An efficient and generally applicable protocol for decarboxylative coupling of α,α‐difluoroarylacetic acids with ethynylbenziodoxolone (EBX) reagents has been developed, affording α,α‐difluoromethylated alkynes bearing various functional groups in moderate to excellent yields. Remarkably, this potassium persulfate (K2S2O8)‐promoted reaction employs water as solvent under transition metal‐free conditions, thus providing a green synthetic approach to α,α‐difluoromethylated alkynes.
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Chemical Synthesis of Rare Natural Bile Acids: 11α‐Hydroxy Derivatives of Lithocholic and Chenodeoxycholic Acids 下载免费PDF全文
Kazunari Namegawa Kyoko Iida Kaoru Omura Shoujiro Ogawa Alan F. Hofmann Takashi Iida 《Lipids》2018,53(4):403-411
A method for the preparation of 11α‐hydroxy derivatives of lithocholic and chenodeoxycholic acids, recently discovered to be natural bile acids, is described. The principal reactions involved were (1) elimination of the 12α‐mesyloxy group of the methyl esters of 3α‐acetate‐12α‐mesylate and 3α,7α‐diacetate‐12α‐mesylate derivatives of deoxycholic acid and cholic acid with potassium acetate/hexamethylphosphoramide; (2) simultaneous reduction/hydrolysis of the resulting △11‐3α‐acetoxy and △11‐3α,7α‐diacetoxy methyl esters with lithium aluminum hydride; (3) stereoselective 11α‐hydroxylation of the △11‐3α,24‐diol and △11‐3α,7α,24‐triol intermediates with B2H6/tetrahydrofuran (THF); and (4) selective oxidation at C‐24 of the resulting 3α,11α,24‐triol and 3α,7α,11α,24‐tetrol to the corresponding C‐24 carboxylic acids with NaClO2 catalyzed by 2,2,6,6‐tetramethylpiperidine 1‐oxyl free radical (TEMPO) and NaClO. In summary, 3α,11α‐dihydroxy‐5β‐cholan‐24‐oic acid and 3α,7α,11α‐trihydroxy‐5β‐cholan‐24‐oic acid have been synthesized and their nuclear magnetic resonance (NMR) spectra characterized. These compounds are now available as reference standards to be used in biliary bile acid analysis. 相似文献
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Romain Blanc Laurent Commeiras Jean‐Luc Parrain 《Advanced Synthesis \u0026amp; Catalysis》2010,352(4):661-666
A new, highly efficient and mild N‐heterocyclic carbene (NHC)‐mediated organocatalytic procedure for the transfer of tin from tributyl(trimethylsilyl)stannane (Bu3SnSiMe3) onto aldehydes for the preparation of α‐silyloxyalkylstannanes and γ‐silyloxyallylstannanes has been developed. 相似文献
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Yanmei Liu Hua Lai Bo Rong Tie Zhou Jia Hong Chao Yuan Shujing Zhao Xiaolong Zhao Biao Jiang Qiang Fang 《Advanced Synthesis \u0026amp; Catalysis》2011,353(17):3161-3165
An efficient strategy for a high‐yielding and stereoselective synthesis of α‐trifluoromethyl unsaturated carboxylic acids directly from the reactions of 3,3,3‐trifluoropropanoic acid (CF3CH2COOH) with various aryl aldehydes in the presence of titanium tetrachloride (TiCl4) is reported here for the first time, which is a valuable expansion for the classical Knoevenagel reaction. Because these compounds may have potential applications in organic electronics and can be easily converted to the corresponding fluorinated alcohols and amino acids with excellent bioactivity, this route should be a good choice for the preparation of α‐trifluoromethyl‐containing derivatives. 相似文献
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BoyapatiM. Choudary Koosam Mahendar M. Lakshmi Kantam Kalluri V.S. Ranganath Taimur Athar 《Advanced Synthesis \u0026amp; Catalysis》2006,348(14):1977-1985
Nanocrystalline magnesium oxide was found to be an effective heterogeneous, solid base catalyst for the one‐pot Wittig reaction to afford α,β‐unsaturated esters and nitriles in excellent yields with high E‐stereoselectivity in the presence of triphenylphosphine under mild conditions. 相似文献
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Zhiqiang Han Wenguo Yang Choon‐Hong Tan Zhiyong Jiang 《Advanced Synthesis \u0026amp; Catalysis》2013,355(8):1505-1511
The first organocatalytic Mannich reaction of 5H‐oxazol‐4‐ones with various readily prepared aryl‐ and alkylsulfonimides has been developed. Two commercially available pseudoenantiomeric Cinchona alkaloids‐derived tertiary amine/ureas have been demonstrated as the most efficient catalysts to access the opposite enantiomers of the Mannich products with equally excellent enantio‐ and diastereoselectivities. From the Mannich adducts, important α‐methyl‐α‐hydroxy‐β‐amino acid derivatives, such as the α‐methylated C‐13 side chain of taxol and taxotere, can be conveniently prepared. 相似文献
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Novel castor oil‐based polyurethane/α‐zirconium phosphate (PU/α‐ZrP) composite films with different α‐ZrP loading (0–1.6 wt %) and different NCO/OH molar ratios were synthesized by a solution casting method. The characteristic properties of the PU/α‐ZrP composite films were examined by Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tensile testing. The results from Fourier transform infrared spectroscopy indicated that strong intermolecular hydrogen bonding formed between α‐ZrP and PU, XRD and SEM results revealed that the α‐ZrP particles were uniformly distributed in the PU matrix at low loading, and obvious aggregation existed at high loading. Because of hydrogen bonding interactions, the maximum values of tensile strength were obtained with 0.6 wt % α‐ZrP loading and 1.5 of NCO/OH molar ratio in the matrix. Evidence proved that the induced α‐ZrP used as a new filler material can affect considerably the mechanical and thermal properties of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
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NataliyaS. Goulioukina GrigoriiN. Bondarenko SergeyE. Lyubimov VadimA. Davankov KonstantinN. Gavrilov IrinaP. Beletskaya 《Advanced Synthesis \u0026amp; Catalysis》2008,350(3):482-492
It was shown that the catalytic hydrogenation of α‐iminophosphonates by molecular hydrogen can serve as a convenient method for the synthesis of racemic and optically active α‐aminophosphonates. Up to 94% ee was achieved in the rhodium‐catalyzed enantioselective hydrogenation using chiral ligand (R)‐BINAP. 相似文献
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Alessandro Palmieri Serena Gabrielli Roberto Ballini 《Advanced Synthesis \u0026amp; Catalysis》2010,352(9):1485-1492
A new class of nitro‐functionalized α,β‐unsaturated esters has been prepared by a regio‐ and diastereoselective Michael addition of nitroalkanes to β‐nitroacrylates, performed at room temperature, under carbonate on polymer as promoter, and in the presence of ethyl acetate as eco‐friendly solvent. Moreover, by the modular choice of the reaction conditions the method allows the synthesis of 1,3‐butadiene‐2‐carboxylates. 相似文献
16.
Koji Yonehara Yasuyuki Miyoshi Aki Tsukajima Takeo Akatsuka Makoto Saito 《Advanced Synthesis \u0026amp; Catalysis》2011,353(7):1071-1075
The methodology in this article is a palladium(II)/copper(II)‐ or palladium(II)‐catalyzed intermolecular cyclization of acrylic acid with alkenes to produce α‐methylene‐γ‐butyrolactone derivatives using molecular oxygen as an environmentally benign oxidant. In this system, the carboxylato, especially trifluoroacetato, or trimethylacetato ligand, plays a quite important role to afford a high catalytic activity by suppressing the deposition of palladium(0) black. 相似文献
17.
Cheonhyoung Park Min Woo Ha Byungsoo Kim Suckchang Hong Doyoung Kim Yohan Park Mi‐hyun Kim Jae Kyun Lee Jeeyeon Lee Hyeung‐geun Park 《Advanced Synthesis \u0026amp; Catalysis》2015,357(13):2841-2848
A new enantioselective synthetic method for the synthesis of α,α‐dialkylmalonates with a quaternary carbon center was developed via α‐alkylation of prochiral malonates by phase‐transfer catalysis (PTC). Asymmetric α‐alkylation of benzylideneamino tert‐butyl α‐methylmalonates under phase‐transfer catalytic conditions in the presence of (S,S)‐3,4,5‐trifluorophenyl‐NAS bromide afforded the corresponding α,α‐dialkylmalonates in high yields (up to 97%) with excellent enantioselectivities (up to 98% ee). The products were then selectively hydrolyzed to chiral malonic monoacids under basic, acidic, or catalytic hydrogenation conditions.
18.
Krishna Bahadur SomaiMagar Yong Rok Lee 《Advanced Synthesis \u0026amp; Catalysis》2014,356(16):3422-3432
Efficient one‐step syntheses of α,β‐ and β,β‐dihaloenones were achieved by ruthenium(II)‐catalyzed reactions between cyclic or acyclic diazodicarbonyl compounds and oxalyl chloride or oxalyl bromide in moderate to good yields. This methodology offers several significant advantages, which include ease of handling, mild reaction conditions, one‐step reaction, and the use of an effective and non‐toxic catalyst. The synthesized compounds were further transformed into highly functionalized novel molecules bearing aromatic rings on the enone moiety using the Suzuki reaction.
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Yi‐Ning Wang Bukuo Ni AllanD. Headley Guigen Li 《Advanced Synthesis \u0026amp; Catalysis》2007,349(3):319-322
The 2‐Ns‐based aminohalogenation of α,β‐unsaturated ketones has been achieved in an ionic liquid, 1‐n‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide {[bmim][N(SO2CF3)2]}. [Bmim][N(SO2CF3)2] was found to be superior not only to classical organic solvents but also to its counterpart, [bmim][BF4], which was proven to be successful in the TsNCl2‐based aminohalogenation but failed to give any product for this reaction. The present process takes the advantage of 2‐NsNCl2 as the stable nitrogen/halogen source in a one‐pot operation without the use of any metal catalysts, it is convenient to perform without special protection of inert gases. Eight examples were examined with good to excellent stereoselectivity (1:5 to one isomer) and modest to good chemical yields (53–72 %). 相似文献
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Monoclinic (α) and hexagonal (β) polypropylene (α‐ and β‐PP) were stained in the vapor of a ruthenium tetroxide solution prepared in situ. The effect of staining on the fusion behavior was investigated using a DSC. A staining duration between 10 and 24 h was found suitable for obtaining a good electron contrast between the crystalline and amorphous regions for TEM examination without causing severe damage to the crystals. The spherulites of the water‐quenched α‐PP were found to be composed of very fine cross‐hatched lamellae whose long period was about 10 nm. In comparison, the β‐PP spherulites crystallized isothermally at 130°C had a category 2 morphology and the lamellae have a long period of 20 nm. The morphology of the spherulite boundary varied depending on the contact angle between the lamellae of the neighboring spherulites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1529–1538, 1999 相似文献