共查询到20条相似文献,搜索用时 62 毫秒
1.
《Polymer-Plastics Technology and Engineering》2013,52(5):931-938
Abstract Unsaturated polyesters were synthesized in the laboratory by the condensation of maleic anhydride and phthalic anhydride with propylene glycol. The condensate obtained was mixed with styrene monomer to get an unsaturated polyester resin formulation. The properties of the polyester resin synthesized were found to be affected by the synthesis parameters. In this study, the effect of sequence of addition of reactants on the properties of resin was investigated. Properties such as tensile strength, tensile modulus, elongation at break, toughness, impact strength, surface hardness, abrasion resistance, and water absorption were evaluated after curing the resin. Propylene glycol necessary for esterification of both the anhydride fractions was initially reacted with phthalic anhydride. Later, the esterification was completed by reaction with maleic anhydride. This sequence of addition of reactants was found to give the best mechanical properties among all possible methods of reactant addition. Moreover, it was found that this sequence of addition of reactants gives the shortest reaction time. 相似文献
2.
Boris E.Krisyuk Danila A.Markin Timofey M.Sypko Viktor V.Zakharov Nikita V.Chukanov Boris L.Korsunskiy 《火炸药学报》2023,(1):31-40
A theoretical and experimental study of the thermal decomposition of nitroguanidine(NQ) has been carried out. Various thermolysis channels were studied by quantum chemistry methods at the CCSD(or DLPNO-CCSD) level using the aug-cc-pVDZ basis set. It is shown that the lowest activation enthalpies(170—180kJ/mol) are characteristic of the reactions of NO2 abstraction from the initial NQ and the reaction channel with the transfer of oxygen from the nitro group to carbon in the limiting st... 相似文献
3.
4.
《Polymer》1987,28(5):683-692
After a short survey of the first indications on the existence of stereoregularity in the main chains of the vinyl polymers, the first syntheses of stereoregular poly(vinylethers) and polystyrene are briefly summarized. The difficulties encountered in the early investigations of the propylene polymerization by the CoO/MoO3/Al2O3 and CrO3/SiO2/Al2O3 catalysts are considered and the isolation and identification of a crystalline component in the mixture of diastereomeric macromolecules thus obtained, are discussed. The results obtained by different research groups, independently investigating the stereospecific polymerization of vinyl monomers, are compared and finally an attempt is made to explore the origin of the very rapid progress made in this field by Natta and coworkers in connection with their discovery of the stereospecific polymerization of α-olefins with the ‘Ziegler-Natta catalysts’. 相似文献
5.
6.
《中国耐火材料》2000,9(2):23-28
Periclase-spinel-carbon brick was made from sintered spinel,fused magnesia and flake graphite as principal raw materials,the influence of Mg/Al(w/w) ratio and the addition of Al,Mg in the matrix of periclas-spinel-carbon brikc on the carbonization and thermal expansion coeffi-cient and the weight los of the brick after heating at 1500℃ in a flowing stream of dry N2for 1.5 h have been studied.The results show that to control Mg/Al(w/w) ration and to add both Al and Mg appropriately can obvi-ously improve the properties of the bricks. 相似文献
7.
LIXiaoming HUANGJin 《中国耐火材料》2000,9(3):21-25
Microstructures of matrixes of a series of high technology castables have been analyzed.In these low cement ,ultra-low cement and non-cement castable matrixes,which were sintered respectively at 1350℃ and 1500℃, silica ulrtafine and α-Al2O3 ultrafine were added ,The results show that the non-cement castable had the best properties at high temerature;adding α-Al2O3 ultrafine was helpful to calcium-feldspar deveoping and growing;and highly purified silica ultrafine stiumulated mullite crystal developing while the common one stimulated its growing. 相似文献
8.
Cerebronic acid (2-hydroxytetracosanoic acid), an α-hydroxy very long-chain fatty acid (VLCFA) and a component of cerebrosides
and sulfatides, is unique to nervous tissues. Studies were carried out to identify the pathway and the subcellular site involved
in the oxidation of cerebronic acid. The results from these studies revealed that cerebronic acid was catabolized by α-oxidation
to CO2 and tricosanoic acid (23:0). Studies with subcellular fractions indicated that cerebronic acid was α-oxidized in fractions
having particulate bound catalase and enzyme systems for the β-oxidation of VLCFA (e.g., lignoceric acid), suggesting peroxisomes
as the subcellular organelle responsible for α-oxidation of cerebronic acid. Etomoxir, an inhibitor of mitochondrial fatty
acid oxidation, had no effect on cerebronic acid α-oxidation. Further, cerebronic acid oxidation was found to be dependent
on the presence of NAD+ but not FAD, NADPH, ATP, Mg2+, or CoASH. Intraorganellar localization studies indicated that the enzyme system for the α-oxidation of cerebronic acid was
associated with the peroxisomal limiting membranes. Studies on cultured fibroblasts from normal subjects and patients with
peroxisomal disorders indicated an impairment of α-oxidation of cerebronic acid in cell lines that lack peroxisomes [e.g.,
Zellweger syndrome (ZS)]. On the other hand, α-oxidation of cerebronic acid was found to be normal in cell lines from X-linked
adrenoleukodystrophy, adult Refsum disease, and rhizomelic chondrodysplasia punctata. Our results clearly demonstrate that
α-oxidation of α-hydroxy VLCFA (cerebronic acid) is a peroxisomal function and that this oxidation is impaired in ZS. Furthermore,
this α-oxidation enzyme system is distinct from the one for the α-oxidation of β-carbon branched-chain fatty acids (e.g.,
phytanic acid). 相似文献
9.
The focus of this study was the effect of spatial confinement on the development of nucleating agent-induced β phase polypropylene (PP) in the dynamically vulcanized thermoplastic elastomers (TPVs) based on dynamically vulcanized PP/ethylene-propylene-diene rubber (EPDM) blend. The melting behaviors, crystalline structures and the morphologies of the blends were studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM). The results indicate that the EPDM phase undergoes a series of changes from the dispersed phase to a continuous one, and again to the dispersed phase with increased content of curing agent, and the PP component always shows itself in a continuous phase. In this process, with the content of the nucleating agent unchanged, the content of β phase PP in the blends initially increases a little and then decreases with increasing PF (Phenolic resin) content. We believe spatial confinement provides a good explanation for the development of β phase PP. 相似文献
10.
The applicability of Zel’dovich’s theory to the propagation velocity of flames with chain-branching reactions was tested by
calculations based on a detailed mechanism and using Zel’dovich’s approximate formulas with a refined mechanism of hydrogen
atom recombination for stoichiometric hydrogen-oxygen and hydrogen-air mixtures at pressures of 47.5–760 torr. Good agreement
of the results was obtained. Zel’dovich’s approximate theory for a flame with chain-branching reactions dominated by recombination
processes gives a reasonable physical picture and provides approximate formulas for flame propagation velocity. 相似文献
11.
In this paper, a model is presented to correlate and predict the swelling behavior of hydrogels in aqueous solutions of electrolytes. The model is a combination of VERS-model, "phantom network" theory and "free-volume" contribution. The VERS-model is used to calculate Gibbs excess energy; "phantom network" theory to describe the elastic properties of polymer network, and "free-volume" contribution to account for additional difference in the size of the species. To test the model, a series of N-isopropylacrylamide based hydrogels are synthesized by free radical polymerization in oxygen-free, deionized water at 25℃ under nitrogen atmosphere. Then, the degree of swelling of all investigated gels as well as the partition of the solute between the gel phase and the surrounding coexisting liquid phase are measured in aqueous solution of sodium chloride. The model test demonstrates that the swelling behavior correlated and predicted by the model agrees with the experimental data within the experimental uncert 相似文献
12.
Sylvie Brochu Rodica Plesu Robert E. Prud'homme Nicolas Spassky Alain Le Borgne 《Polymer Bulletin》1993,30(2):223-228
An octakis (3-O-butyryl-2,6-di-O-pentyl)--cyclodextrin capillary gas chromatographic column was used to determine the optical purity of seven different -lactones, having substituents in - or -position, and DL-lactide. The resolving power varied from one lactone to another. The optical purity values determined by GC were in agreement with those obtained from NMR spectroscopy or optical rotation. 相似文献
13.
Refractories and Industrial Ceramics - 相似文献
14.
《Electrochimica acta》1986,31(11):1449-1455
Thermodynamic ionization constants, TpKa, of several fluorinated β-diketones, viz. 2-furoyltri-fluoroacetone, heptafluorobutrylpivaloyl methane, hexafluoroacetylacetone, 2-thenoyltrifluoroacetone and trifluoroacetylacetone have been determined pH-metrically in 0-70vol.% dioxane-water mixtures at 25 and 35±0.01°C applying an empirical pH correction for mixed hydro-organic media. The pKas in aqueous medium (at 0% dioxane) are obtained following the method of extrapolation and least-squares. All of them are very weak monoprotic acids. TpKas do not vary linearly with the reciprocal of dielectric constant of the medium, but a plot of TpKavs the mole fraction of dioxane is linear at a given temperature. The “true constant” K′a and solvation number, n, in the expression (H+)(A−)/(HA)=K′a(S)n=K*a for these reagents have been evaluated by analysing the experimental data mathematically. Values of ΔG°, ΔH° and ΔS° are also computed. Positive values of ΔH° found in aqueous-dioxane media for the above fluorinated derivatives, except HFOD, indicate the endothermicity of the proton enolization reactions. Temperature, medium as well as substituent effects are briefly discussed. 相似文献
15.
YEFangbao RigaudM. 《中国耐火材料》2003,12(3):7-12
Rheology of castables is greatly affected and cantrolled by rheological behavior of their matrix,In this work,the rheological properties of bauxite-based castable matrix have been studied.The effecfts of super-fine silica and alumina addition,water/cemenl ratio,dispersants and baurite particle-size on viscosity,shear rate and shear stress of the slurries have been investigated.Based on these results,the range of optinium composition of the matrix with good rheological behavior has been obtained. 相似文献
16.
Zoon Ha Ryu Sang Wok Lee Malcolm J. D��Souza Lamia Yaakoubd Samantha E. Feld Dennis N. Kevill 《International journal of molecular sciences》2008,9(12):2639-2657
Additional specific rates of solvolysis have been determined, mainly in fluoroalcohol containing solvents, for benzenesulfonyl chloride (1) and p-nitrobenzene-sulfonyl chloride (2). For trans-β-styrenesulfonyl chloride (3), a study has been carried out in 43 pure and binary solvents, covering a wide range of hyroxylic solvent systems. For the specific rates of solvolyses of each of the three substrates, a good correlation was obtained over the full range of solvents when the extended Grunwald-Winstein equation was applied. The sensitivities to changes in solvent nucleophilicity and solvent ionizing power are similar to values determined earlier and an SN2 process is proposed. For 3, kinetic solvent isotope effects of 1.46 for kH2O/kD2O and 1.76 for kMeOH/kMeOD were determined. These are also compared to literature values for other sulfonyl chlorides. 相似文献
17.
18.
G. L. Pashkov S. V. Saikova M. V. Panteleeva E. V. Linok 《Theoretical Foundations of Chemical Engineering》2014,48(5):671-676
An anion-exchange method for synthesizing nickel hydroxide using industrial strongly basic AV-17-8 anionite has been proposed. The influence of conditions (concentration and nature of starting salt, amount of the anionite, process duration, etc.) on the precipitate yield has been established. The product has been investigated by scanning electron microscopy, IR and Raman spectroscopy, X-ray phase analysis, and thermal and chemical analyses. It has been established that the product is a disordered layered modification of nickel hydroxide α-Ni(OH)2, which contains anions and water molecules in the interlayer spacing. Nickel hydroxide particles are needle crystals (40–80 nm) that form agglomerates 0.3–0.5 μm in size. 相似文献
19.
Two series of sulfated zirconia have been prepared by immersing amorphous or crystalline zirconia in an H2SO4 solution (0.25–2.5 M). They were compared with a commercial sulfated zirconium hydroxide. Activation temperature was varied between 300 and 725°C. Sulfate density varied so that the mean surface area of an individual sulfate ranged from 0.14 to 0.54 nm2. Three limiting sulfate states are evidenced and characterized by TPRMS. Catalysts are tested for isomerization of nhexane at 150°C and 3 MPa. Factors influencing the activity are discussed. The data show that a highly active and selective catalyst for producing hexane isomers requires tetragonal zirconia with a sulfate occupancy of about 0.40 nm2. Preparation parameters must therefore be adapted to match these constraints. 相似文献
20.
Maaike K. Ramseier 《臭氧:科学与工程》2009,31(3):201-215
Organic acids are part of assimilable organic carbon (AOC) formed from natural organic matter (NOM) during ozonation for drinking water production. To elucidate the formation of organic acids, phenol as surrogate compound for NOM was ozonated while suppressing reactions of ·OH radicals by addition of tert-butanol. Batch experiments show benzoquinone (40 and 18%), catechol (33 and 1%), cis,cis-muconic acid (6 and 3%), and hydroquinone (2 and 7%) to be the most abundant primary products at pH 7 and 3, respectively. The tertiary product oxalic acid was obtained in similar yields from phenol ozonation (0.8%) as during ozonation of lake water (1.6%). Together with other low molecular weight organic acids it was formed upon small ozone exposures, as was shown by time-dependent experiments in time ranges of 0.4–23 and 0.07–1.0 seconds for pH 3 and 7.25, respectively. 相似文献