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It is possible to optimize the performance of the inorganic-organic composites dispersing the inorganic component in the organic matrix on a nanomiter length scale. If dry the inorganic phase cannot be intimately dispersed during the incorporation in the matrix. When the particle surface is organically modified, and the incorporation is made starting from a liquid dispersion (particles in polymer solution), the resulting composites exhibit an excellent homogeneity. Here, monolithic [poly(methyl methacrylate)/monodisperse silica particles] nanocomposites have been prepared and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), micro-hardness, and differential scanning calorimetry (DSC). 相似文献
24.
V. A. Roginsky T. K. Barsukova A. A. Remorova W. Bors 《Journal of the American Oil Chemists' Society》1996,73(6):777-786
The relative reactivities as well as the stoichiometric coefficients for a number of flavonoids, catechols, and—for comparison—standard
phenolic antioxidants were determined by analyzing the kinetics of oxygen consumption in organic and micellar systems, with
peroxidation initiated by lipid- and water-soluble azo initiators. The results demonstrated that the flavonoids did not behave
as classic phenolic antioxidants such as α-tocopherol, but showed only moderate chain-breaking activities. The results were
in line with other structure-activity relationship studies on the importance of the B-ring catechol structure, the 2,3-double
bond, and the 3,5-hydroxy groups. The data are discussed in view of possible explanations of the deviations flavonoids reveal
in their behavior compared with regular phenolic antioxidants. 相似文献
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醋酸甲酯在Cs_(1.5)PW/SiO_2催化剂上的水解反应 总被引:1,自引:0,他引:1
通过改变阳离子的种类与配比,制备了一系列SiO2负载的磷钨酸盐催化剂,考察了制备方法对催化剂性能的影响,采用傅里叶变换红外光谱、X射线衍射、X射线荧光光谱、环境扫描电子显微镜等方法对催化剂进行了表征,并考察了该系列催化剂对醋酸甲酯水解反应的活性。实验结果表明,Cs1.5PW/SiO2催化剂的活性最好,当Cs1.5PW负载量(质量分数)为30%时,Cs1.5PW的Keggin结构保持完好,没有硅钨酸阴离子形成,Cs1.5PW在SiO2载体上高度分散;在反应温度55℃、反应时间2h的条件下,醋酸甲酯的转化率为35.79%,约为均相磷钨酸催化剂的1.3倍。该催化剂重复使用4次后,醋酸甲酯的转化率稳定在25%;80℃下反应2h,与NKC-9磺酸树脂催化剂相比,醋酸甲酯的转化率提高了5.17%。 相似文献
27.
Thermodynamic parameters have been determined for the interaction of methyl orange and poly(vinylpyrrolidone) in aqueous solutions containing tris, tris and hydrochloric acid, or water only. Enthalpy changes were determined by use of a flow microcalorimeter. Free energy changes were calculated from the results of equilbrium dialysis studies. The results are interpreted in terms of the behaviour of poly(vinylpyrrolidone) in these systems. Analysis of data shows that the hydrophobic interactions in the systems are in the order: tris > wateronly > tris-HC1. 相似文献
28.
Dominique PinoitRobert E Prud'homme 《Polymer》2002,43(8):2321-2328
The phase behavior of ternary blends made of poly(epichlorohydrin) (PECH), poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) has been investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). DMTA measurements have been shown to be more sensitive than DSC for the detection of a second phase, for the determination of the composition of each phase, and the distribution of PECH in each of them. About 70% PECH was required to obtain a single narrow Tg in the ternary system, which suggests a single homogeneous phase in the limit of sensitivity of DMTA. This study also emphasizes the importance of the composition of the immiscible polymer pair (i.e. the PVAc/PMMA pair in the PECH/PVAc/PMMA system), in addition to the thermodynamic interaction parameters, for controling the phase behavior of ternary systems. 相似文献
29.
The large-deformation three-dimensional glass-rubber constitutive model for isotropic, amorphous, linear polymers near the glass transition, previously proposed, has been extended to include a spectrum of network relaxations. In addition, an experimental programme of uniaxial tension and compression tests was carried out on high molecular weight cast sheets of poly(methyl methacrylate) (PMMA), with varying strain-rate and temperature across the range from 114 to 190 °C, encompassing the thermoforming range of practical importance. The extended model was found to fit successfully the data for PMMA, provided a doublet network relaxation spectrum was employed. The original model, with only a single network relaxation, was found to be grossly inadequate when there was significant network relaxation by entanglement slippage. Parameters of the model for PMMA, obtained by fitting to the new data, were compared with values obtained by other routes. 相似文献
30.
Ke-Shun Liu 《Journal of the American Oil Chemists' Society》1994,71(11):1179-1187
Theoretically, preparation of fatty acid methyl esters (FAMEs) deals with reversible chemical reactions in a complex system.
Methodologically, there are numerous ways, generally characterized by the type of catalysts used and steps involved. Although
there are more than a half dozen common catalysts, the majority fall into either acidic (HCl, H2SO4 and BF3) or alkaline types (NaOCH3, KOH and NaOH), with each having its own catalytic capability and application limitations. In terms of steps, many conventional
methods, including those officially recognized, consist of drying, digestion, extraction, purification, alkaline hydrolysis,
transmethylation/methylation and postreaction work-up. Although these methods are capable of providing reliable estimates
if some precautions are taken, they are cumbersome, time-consuming and cost-inefficient. A new approach has been to transmethylate
lipidsin situ. Due to its simplicity, high sensitivity, comparable reliability and capability to determine total fatty acids, the method
of direct transmethylation is finding a unique place in lipid determination. Regardless of which method is used, quantitative
methylation requires chemists to take precautions at every step involved, particularly during FAME formation and subsequent
recovery steps. Evidently, there is an urgent need for more systematic studies, guided by the chemical principle of reactions
involved and physicochemical properties of regents and end products, into factors affecting these steps. Hopefully, this will
lead to an improved method, which measures lipid composition in biological materials not only with high accuracy but also
with high efficiency and minimum costs. 相似文献