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排序方式: 共有365条查询结果,搜索用时 31 毫秒
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Pauline L. Nasatto Frédéric Pignon Joana L. M. Silveira Maria Eugênia R. Duarte Miguel D. Noseda Marguerite Rinaudo 《International Journal of Polymer Analysis and Characterization》2015,20(2):110-118
In this study, thermogelation of methylcelluloses is investigated in relation to the molar mass and concentration in aqueous medium. A large hysteresis between heating and cooling ramps was observed whatever the conditions. The heating process in particular was studied to analyze the two steps of gelation using rheometry. At low temperature, in the sol state, viscosity depends on the concentration and molar mass. Over 30°C a gel-like behavior was observed including two steps (the second step is a strong gel with phase separation) having storage moduli that are nearly independent of polymer molar mass but are directly related to polymer concentration. 相似文献
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Eléonore Mathis Marie-Laure Michon Claude Billaud Pauline Grau Anthony Bocahut Caroll Vergelati Didier R. Long 《Journal of polymer science. Part A, Polymer chemistry》2020,58(8):1177-1188
Thermoset (TS) epoxy resins can be toughened with a thermoplastic (TP) for high-performance applications. The final structure morphology has to be controlled to achieve high mechanical properties and high impact resistance. Four polyethersulfone-modified epoxy resins are considered. They consist of different epoxy monomer structure (TGAP, triglycidyl-p-aminophenol and TGDDM, tetraglycidyl diaminodiphenylmethane) and a fixed amount of thermoplastic, and they are cured with two different amounts of curing agent. A reaction-induced phase separation occurs for all formulations generating morphologies, different in shapes and scales. The aim is to control the final morphology and in particular its dominant length scale. This morphology depends on the phase separation process, from the initiation to its final stage. The initiation relies on the relative miscibility of the components and on the stoichiometry between epoxy and curing agent. The kinetics depends on the viscosity of the systems. The different morphologies are characterized by electron microscopy or neutron scattering. Dynamic mechanical analysis allows confirming the presence of a phase separation even when it is not observable by electron microscopy. Vermicular morphologies with few hundreds nanometer width are obtained for the systems containing the TGAP as epoxy monomer. Systems formulated with TGDDM presents morphologies on much smaller scale of order a few tens of nanometers. We interpret the different sizes of the morphologies as a consequence of a larger viscosity for the TGDDM systems as compared to the TGAP ones rather than by a latter initiation of phase separation. 相似文献
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Muñoz-Villamizar A. Santos J. Grau P. Viles E. 《Central European Journal of Operations Research》2021,29(4):1219-1230
Central European Journal of Operations Research - Environmental efficiency should not be treated independently of production efficiency. Several studies have demonstrated that lean management can... 相似文献
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Dr. Elizabeth H. Krenske Sarah Lam Jerome P. L. Ng Brian Lo Dr. Sze Kui Lam Prof. Dr. Pauline Chiu Prof. Dr. Kendall N. Houk 《Angewandte Chemie (International ed. in English)》2015,54(25):7422-7425
Silyl‐triflate‐catalyzed (4+3) cycloadditions of epoxy enolsilanes with dienes provide a mild and chemoselective synthetic route to seven‐membered carbocycles. Epoxy enolsilanes containing a terminal enolsilane and a single stereocenter undergo cycloaddition with almost complete conservation of enantiomeric purity, a finding that argues against the involvement of oxyallyl cation intermediates which have been previously proposed for these types of reactions. Reported are theoretical and experimental investigations of the cycloaddition mechanism. The major enantiomers of the cycloadducts are derived from SN2‐like reactions of the silylated epoxide with the diene, in which stereospecific ring opening and formation of the two new C? C bonds occur in a single step. Calculations predict, and experiments confirm, that the observed small losses of enantiomeric purity are traced to a triflate‐mediated double SN2 cycloaddition pathway. 相似文献
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Audrey Llevot Etienne Grau Stphane Carlotti Stphane Grelier Henri Cramail 《Macromolecular rapid communications》2016,37(1):9-28
Nowadays, the synthesis of (semi)aromatic polymers from lignin derivatives is of major interest, as aromatic compounds are key intermediates in the manufacture of polymers and lignin is the main source of aromatic biobased substrates. Phenols with a variety of chemical structures can be obtained from lignin deconstruction; among them, vanillin and ferulic acid are the main ones. Depending on the phenol substrates, different chemical modifications and polymerization pathways are developed, leading to (semi)aromatic polymers covering a wide range of thermomechanical properties. This review discusses the synthesis and properties of thermosets (vinyl ester resins, cyanate ester, epoxy, and benzoxazine resins) and thermoplastic polymers (polyesters, polyanhydrides, Schiff base polymers, polyacetals, polyoxalates, polycarbonates, acrylate polymers) prepared from vanillin, ferulic acid, guaiacol, syringaldehyde, or 4‐hydroxybenzoic acid.
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In this paper we present an algorithm, inspired by the cyclic coordinate descent method, which allows the solution of hydrothermal
optimization problems involving pumped-storage plants. The proof of the convergence of the succession generated by the algorithm
was based on the use of an appropriate adaptation of Zangwill’s global theorem of convergence. Finally, the algorithm proposed
is implemented using the Mathematica Package and is applied to an example to illustrate the results obtained. 相似文献
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