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The calorimetric determination of the ceiling temperature for the chemical polymerization of pyrrole
S. Cavallaro A. Colligiani G. Cum S. Foti 《Journal of Thermal Analysis and Calorimetry》1995,44(2):269-280
The previously found strong dependence of the polymerization enthalpy on the reaction temperature has been rationalized. The temperature dependence is to be ascribed to the existence of a ‘ceiling temperature’ for the polymerization process of the pyrrole monomer. The determined ceiling temperature has beenT?350 K when FeCl3 was used as the oxidizing agent in CH3CN solution. The existence of a ceiling temperature together with its already determined exoenthalpic nature allows to classify the polymerization reaction as an exoentropic one. From the dependence of the yield of insoluble polymer on the reaction temperature, the trend of the relative mean numeral molecular massM n for the different obtained polymers has been determined. Measurements of electrical conductivity on pressed pellets of the different polymers allowed to establish a correlation between theM n value and the conductivities The dependence of the conductivity on the exposition time to the air allowed to do some essays on the aging behaviour of the obtained polypyrrole. By making some assumptions, an absolute calorimetric determination of the value ofM n of polypyrrole was tempted together with that of the related poly-N-vinilpyrrole. 相似文献
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科学本质和人文素养是科学教育关注的热点.科学史中蕴含着丰富的科学本质观和人文内涵.通过对氟元素发现史的考证分析,发现其中蕴含着"科学知识的实证性、科学知识的主观性、科学方法的多元化以及科学研究需要想象力和创造力"等科学本质观,承载着"科学发展离不开信息交流、科学发展需要勇于献身的科学精神以及科学发展表现为继承和创新的统... 相似文献
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锌在植物中的形态及生理作用机理研究进展 总被引:27,自引:1,他引:26
对锌在植物中的形态及锌在植物生理过程中的作用机理进行了综述和讨论,表明锌对碳水化合物代谢,蛋白质代谢,植物生长素代谢及细胞膜的功能和结构有很大影响。此外,锌与植物病害也有很大关系。 相似文献
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Thermodynamic properties of fluids are generally calculated from the PVT relations through equations of state. The majority of existing equations of state require the critical properties or intermolecular potential energy parameters as their input data. In many cases, such properties are neither available nor they can be accurately estimated.
One accessible and accurately measurable property of substances is the velocity of sound. In this report a method is introduced through which one can predict the PVT behavior of fluids using the velocity of sound data. A general mathematical relationship,
expressing the velocity of sound, c, in terms of the hard-core velocity of sound, chs, and thermodynamic properties is derived. One may use this equation to extract PVT data from cVT data, or vice versa. As an example the virial coefficients, the Lennard-Jones intermolecular potential parameters, and the constants of the van der Waals equation of state for a number of pure fluids are calculated using the velocity of sound data. Utility of this method is particularly attractive for such compounds as heavy hydrocarbons, unstable fluids, and newly designed molecules for which intermolecular parameters and critical properties are not available. 相似文献7.
Wu-Hsiung Ho 《中国化学会会志》1987,34(4):257-261
The kinetics of the sulfation of 2-octanol by sulfamic acid in dimetylformamide were studied. The rate of disappearance of sulfamic acid obeys the rate equation: Rate=k[SA] where [SA] is the concentration of sulfamic acid. The energy and entropy of activation are 3.1 ± 0.6 kcal/mol and 15±2eu A possible mechanism is as follows: The sulfamic acid reacts with DMF to form DMF·SO3 which then reacts rapidly with 2-octanol to form ammonium sec-octyl sulfate. The kinetics of the sulfation of 2-octanol by sulfamic acid in dimethyl sulfoxide were also studied. The reaction is described by a similar first-order equation. The energy and entropy of activation are 33.7±1.0 kcal/mol and 17±3eu. 相似文献
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S. Blacher F. Brouers R. Fayt P. Teyssi 《Journal of Polymer Science.Polymer Physics》1993,31(6):655-662
It has been demonstrated that use of polymeric emulsifiers under usual processing conditions in the melt state is a powerful technique for preparing polymer alloys. Digitized representation of optical micrographs of thin sections of blends of a low-density polyethylene and polystyrene (20 wt % PE-80 wt % PS) containing 2 and 5 wt % of two hydrogenated polybutadiene-polystyrene block copolymers exhibit different degrees of homogeneity as well as different morphological structures which can be studied by a multifractal analysis. We show how these differences are reflected in the f(α) spectrum of singularities which can be obtained by a box counting method in the canonical approximation. We have found a correlation between the f(α) curves and the mechanical properties of the corresponding samples: the samples which area the less multifractals have the best mechanical properties. © 1993 John Wiley & Sons, Inc. 相似文献
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The protonation of leucoemeraldine in power form and in N-methylpyrrolidinone (NMP) solution by HCIO4 and HBF4 has been studied by x-ray photoelectron spectroscopy (XPS), infrared (IR), and ultraviolet (UV)-visible absorption spectroscopy. In powder form, less than 25% of the amine nitrogens can be protonated in the absence of oxygen. The effects of oxygen on the degree of protonation and the distribution of amine and imine units upon deprotonation of the salt are investigated. The degree of protonation in leuccemeraldine can be increased to about 50% with 3 M HCIO4, similar to that achievable with emeraldine base in powder form. In NMP solution, leucoemeraldine is easily oxidized by dissolved oxygen. Protonation of both leucoemeraldine and emeraldine base in NMP solutions results in metastable species which gradually undergo deprotonation. The resulting products are affected by the O2 content of the solutions. © 1993 John Wiley & Sons, Inc. 相似文献
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自从1964年Lentz等人提出三甲基硅烷化(TMS)方法研究硅酸盐结构后,人们意识到这种方法能够较真按着地反映硅酸盐结构及聚合状态。又由于硅烷化所得的衍生物(硅酯)易溶于有机溶剂,可以采用多种方法进行分析鉴定。本文应用TMS-GLC及TMSGPC二种方法研究了ZSM-5沸石生成过程中液相硅酸根离子聚合状态的变化。 相似文献
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Hans-Jürgen Quadbeck-Seeger 《Angewandte Chemie (International ed. in English)》1990,29(11):1177-1188
A particularly close relationship exists between chemistry, the science of the transformation of matter, and developments in human living conditions. Though little more than 150 years old, chemical technology has had a greater influence on our civilization than any other technological discipline. Its roots lie not in the crafts, but in scientific research. Relationships derived from the laws of nature were taken as a basis for the systematic solution of practical problems. It is to this strategy that chemistry owes its success. New opportunities arise from new discoveries. These result from basic research at universities, research institutes, and industrial laboratories. Applied research in turn transforms the discoveries into innovative solutions to problems on an industrial scale. The objectives of applied research are oriented toward the marketplace and to the needs of mankind. Our knowledge of scientific interrelationships has been growing with unabated vigor for decades, but so too has our insight into the enormous complexity of the material world. Many of the problems that civilization faces result from the fact that our knowledge is still inadequate. Intensive research and development offer the only hope for progress. Scientists must of course act responsibly with the knowledge they acquire, and they must provide the information necessary to establish public confidence in their methods and products. This is the prerequisite for broad acceptance of technological progress, and given the extent of the world's population no alternative to progress exists. The shape of that progress is also subject to influences outside the realm of science, however, including social norms and political activities. A country that is not rich in raw materials, like the Federal Republic of Germany, must pay particular attention to these factors as well if it is to maintain its innovative strength. 相似文献
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高等师范院校化学类专业建设有其自身特有的发展历史,同时也表现出与综合类高校化学类专业所不同的办学特色。为了实现特定的人才培养目标,高师化学类专业需要形成"通识类+专业主干类+个性发展类"课程体系,同时根据不同类型学生的发展特点和需要对各个模块进行具体化设计。高师化学类专业课程教学既要体现化学学科思维,又要体现现代教育理念和方法,努力将化学学科的研究过程及其特点与学科教学过程与方法有机地整合,达到深度融合。 相似文献
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The determination of the number of components in a mixture is an important tool for qualitative and quantitative analysis in spectroscopy. The accuracy of nine selected indices for an estimation of the number of components that contribute to a set of spectra was critically tested on experimental data sets of protonation equilibria of four drugs using the INDICES algorithm in S-Plus. Methods are classified into two categories: precise methods based on a knowledge of the instrumental error of the sabsorbance data, sinst(A), and approximate methods requiring no such knowledge. Indices of precise methods predict the correct number of components, even the presence of a minor one, when the quality of data is high and instrumental error is known. Improved identification of the number of species uses the second or third derivative function for some indices, namely when the number of species in the mixture is higher than four and when, due to large variations in the indicator values even at logarithmic scale, the indicator curve does not reach an obvious point where the slope changes. The number of variously protonated components and their dissociation constants for four drugs—mycophenolate, ambroxol, silybin and silydianin—at 25 °C were determined using SQUAD(84) regression and INDICES principal component analysis of the pH-spectrophotometric data. A proposed strategy of efficient experimentation in protonation constants determination, followed by a computational strategy, is presented with the goodness-of-fit tests for various regression diagnostics enabling the reliability of parameter estimates to be accessed. 相似文献
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简要介绍2010年度国家自然科学基金资助情况,分析基金申请与学科发展存在问题;概述学科前沿与发展战略等;通报2011年项目指南. 相似文献
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The bioavailability of pharmaca which dissolve in water only with difficulty is very limited. The cyclodextrins /CDs/, and primarily -CD and -CD, were successfully applied to increase the dissolution characteristics and hence the bioavailability of drugs: furosemide, hydrochlorothiazide, mebendazole, metronidazole, spironolactone, tofisopam, vinpocetine base, etc. From these pharmaca, products were made by mixing, kneading, grinding, freeze-drying, spray-embedding and precipitation.The more important factors on which the dissolution and bioavailability of the drugs depend are concluded. 相似文献
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Summary By identification of the essential oil component ‘cis-sabinene hydrate acetate’ of marjoram we demonstrate that the mass spectrum—furnish
to the chemical composition and molecular configuration of compounds—can lead to incorrect qualitative identification if retention
data are not taken into consideration. We studied also the temperature-dependence of the retention data of different compounds,
and our measurements showed that because of the different temperature-dependence, a change in the temperature of the analysis
results in a change in order of elution. The use of this phenomenon, originating from the change of the retention data, both
increases the safety of qualitative identification and aids determination of the optimum measurement conditions in both isothermal
and temperature-programmed modes of operation.
Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001 相似文献
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R. M. Lazorenko-Manevich A. N. Podobaev L. A. Sokolova 《Russian Journal of Electrochemistry》2007,43(1):42-50
Based on the model of spatial separation of the dissolution and passivation of hydrophilic metals, the effect of strong specific adsorption of anions on the shape of curves for the relaxation of anodic current of metals in acid solutions after switching an anodic activation pulse off is considered by using iron as an example. 相似文献
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A. V. Tvardovskii A. A. Fomkin Yu. I. Tarasevich I. G. Polyakova V. V. Serpinskii I. M. Guseva 《Russian Chemical Bulletin》1992,41(6):987-991
The changes in the thermodynamic functions of the sorbents were calculated for the first time from measurements of the deformations of vermiculite during the sorption of water vapor and adsorption-calorimetric data.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Institute of Colloid Chemistry and the Chemistry of Water, Academy of Sciences of the Ukraine, 252180 Kiev. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1270–1275, June, 1992. 相似文献