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1.
Two types of the regular copolymer of poly (1, 4-phenyleneterephthalamide) were synthesized by the low temperature solution polycondensation in NMP-CaCl_2 solvent system, using the piperazine or 2,5-dimethylpiperazine as the third components introduced in the main chain of poly (1, 4-phenyleneterephthalamide). The properties of copolymers were characterized by IR, SEM, X-RAY diffraction, polarizing microscopy, TGA and solubilities.Experimental results showed that the copolymers had good solubility and thermal stability, the concentrated sulfuric acid (~98% ) solution of regular PPTA copolymers had liquid crystalline proper- 相似文献
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详细地研究了对苯二甲酰-对苯二胺低温溶液缩聚时,各种反应条件对聚合体分子量的影响,获得了适合于液晶纺丝的高分子量聚合体,其η_(inh)可达5—7。结果表明,聚合体系的水份、单体克分子浓度、各种混合溶剂体系比对聚合体分子量有明显的影响。为获得高分子量聚合体,混合溶剂体系的最佳组成分别为:HMPA:DMAC=4:1(体积比)、HMPA:NMP=7:3 和 HMPA:THF=9:1。当水份含量大于100ppm时,将严重妨碍高分子量聚合体的得到。在缩聚反应初期,聚合体η_(inh)随时间迅速增长,两三分钟内出现凝聚现象,聚合转化率达100%。体系凝聚后缩聚反应仍然进行,聚合体仍有增长。 相似文献
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Electron diffraction investigation of PPTA/nylon 3T blends from shear-oriented anisotropic solutions
Nematic solutions of PPTA and nylon 3T were prepared in H2SO4 Optical microscopy was used to ascertain the phase behaviour of the blends. In the studied concentration range, no phase separation was observed. The solutions were shear-oriented and coagulated, and the resulting samples were studied by x-ray and electron diffraction. Nylon 3T crystallised even at a low concentration, which is indicative of a phase separation. Electron diffraction investigations of the oriented samples showed that well-oriented areas, which were predominantly composed of PPTA, adjoined areas where the major component, nylon 3T, showed no orientation. The relative proportion of the unoriented areas increased with increasing nylon concentration. It was concluded that, upon coagulation, the nylon was segregated into separate phases and crystallised unoriented, whereas for PPTA, crystallisation proceeded with very little chain rearrangement therefore preserving the orientation. 相似文献
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In this study,we compared the effect of n-pentane and ice-water bath on removing the thermal effect in the poly(p-phenylene terephthalamide)(PPTA) polymerization process.The results indicate that the n-pentane can help to transfer the reaction heat faster and better.Adding suitable amount of n-pentanes into the PPTA preparation process not only improve the heat transfer,but also reduce the motor power in the polymerization process.Moreover,the introduction of n-pentane properly does not result in decrease of the inherent viscosity(ηinh) of polymer.Instead,it leads to increased viscosity of polymer during the PPTA preparation process.The results indicate that n-pentane can effectively transfer the reaction heat and avoid overheating during the polymerization of PPTA. 相似文献
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Dalmo Mandelli Rafael A. Steffen Georgiy B. Shul''pin 《Reaction Kinetics and Catalysis Letters》2006,88(1):165-173
Summary Epoxidation of natural terpene (+)-carvone by the system consisting of a catalyst, oxalic acid (co-catalyst) and H2O2 (70% aqueous solution; oxidant) was studied and factorial design methods were applied for the optimization of this reaction.
A dinuclear manganese(IV) complex [LMn(O)3MnL](PF6)2 (L = 1,4,7-trimethyl-1,4,7-triazacyclononane) was used as a catalyst, and acetonitrile was employed as a solvent. An analysis
by methods of the complete 24 factorial design showed that an increase in the catalyst concentration gives a strong positive effect on the carvone conversion
and selectivity. Hydrogen peroxide has a smaller positive effect on the conversion, but at high concentration, H2O2 leads to some decrease in the selectivity. An increase in the oxalic acid concentration has a beneficial effect on the conversion,
but does not affect the selectivity. 相似文献
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Previous pulsed NMR studies of polyisoprene have largely been concerned with entangled or crosslinked networks. This paper deals with (i) the relaxation of high molecular weight entangled; (ii) cross-linked; (iii) monodisperse low molecular weight; and (iv) high molecular weight polymer in the presence of tetrachloroethylene which, by increasing molecular mobility, can be expected to influence the NMR relaxation. For all four types of polyisoprene, the spin-lattice T1, relaxation shows a minimum with position depending only on the free volume, as influenced by changes in temperature T and polymer concentration v1,. For monodisperse polyisoprene of molecular weight 7200, insufficient to form an entangled network, the spin-spin relaxation decay constant T2L is quantitatively related to the free volume 1 by two parameters A′ and B″ when the free volume is altered by a change in temperature, or in polymer concentration (10–100/). This can also be expressed in the form where the parameter T∞ at 100% concentration agrees with the value used to describe rheological properties. At other concentrations of polymer, T∞ and B′ can be derived quantitatively from the coefficients of volume expansion of polymer and solvent. The variation of T2L with molecular weight (T2L ∝ M?0.5) occurs via the A′ parameter. It is concluded that T2L can be quantitatively related to the free volume available for molecular motion (as influenced by temperature and solvent concentration) as well as to molecular weight. Furthermore T2L is simply related to viscosity n, over a wide range of temperatures and concentrations. T2 can be used to analyse the molecular motions involved in theology. 相似文献
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Takao Ikariya Yasutoshi Ishikawa Kiyomiki Hirai Sadao Yoshikawa 《Journal of organometallic chemistry》1985,288(3):311-315
The reaction of WCl6/LiAlH4 with imines, R′NCHR, gave tertiary amines, R′N(CH2R)2, and secondary amines, R′NHCHRCH2R. Isotope labeling experiments revealed that the reaction involved two types of azatungstenacyclobutanes, HR and HR, produced from the reaction of an alkylidene tungsten intermediate with the imine CN double bond. Formation of these metallacyclobutanes is highly dependent on the solvent used. 相似文献
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Abstract— The present study attempts to correlate the phosphorescence life time τp at 77°K of a definite solute: tetramethylparaphenylenediamine (TMPD) with various solvents viscosity and polarity. A few experiments with benzene in the same solvents are also reported. The following results have been obtained:
- 1 The measured τp vary regularly with the sample immersion time in liquid N2, reaching a constant value after a few hours. This effect is related to the glass matrix relaxation. The rate constant Kisc (S, 1→T1) is also found to vary during relaxation of the solvent.
- 2 In the expression giving the nonradiative rate constant Knr (T1→S0), the bimolecular quenching term appears negligible for high viscosity matrices i.e. for η= 109 poises for benzene and for TMPD. Knr is found to vary linearly with log η, as well as the intersystem crossing S1→T1 rate constant Kisc.
- 3 Both Knr (T1→S0) and Kisc (S1→T1), increase with decreasing polarity of the solvent.
- 4 From our own observations and literature data[6] for C6H6 it appears that solvent viscosity does not contribute appreciably to the observed temperature effect on the solute τp when only a monomolecular triplet deactivation is operative.
11.
A number of lines from a CO2 TEA laser were used to photolyze CF2Cl2. Enrichment of the 35Cl and 37Cl isotopes in the molecular chlorine formed during the photolysis was observed using a mass spectrometer. Maximum enrichment was about 1.8. The dependence of enrichment on wavelength, reactant concentration, inert gas pressure, and the presence of SiF4 is reported. Of particular interest is the persistence of significant enrichment at pressures up to several hundred torr (≈ 105 Pa). Aside from the practical significance of this enrichment at high pressures, it suggests that there are important contributions from isotopically specific interactions after the laser pulse. 相似文献
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Experiments show that transversally applied magnetic field H of strength 12 kG at 10, 15, 20, 25, 30, 40 and 60°C and the ambient pressure decreases the viscosity of high concentration Mn(NO3)2H2O solution. The largest value of this decrease occurs at the temperature range of 20–25°C. On the other hand, at low paramagnetic ion concentrations, the applied magnetic field increases the viscosity of Mn(NO3)2H2O solution in such a way that the observed effect value in the limit seems to approach the already measured viscosity increase of the pure water. However, the temperature dependence of the observed viscosity increase of the given dilute paramagnetic Mn(NO3)2H2O solution appears to be more complex and at some temperature even opposite to that already shown viscosity—temperature behavior of the diamagnetic pure water. 相似文献
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Christy R. Vestal 《Journal of solid state chemistry》2003,175(1):59-62
Magnesium-aluminum oxide, MgAl2O4 spinel nanoparticles have been synthesized using normal micelle microemulsion methods. A mixed magnesium-aluminum hydroxide is initially formed which after annealing at 600°C forms nanocrystalline MgAl2O4 spinel. By controlling reactant concentration in the micelle solution, the particle size has been tuned over the range 4-20 nm. The reaction pathways have been determined by using the characterization methods such as X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry. 相似文献
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The effect of solvent salt cation, temperature of electrolysis, and cathodic deposition potential to basic characteristics
of uranium dioxide potentiostatic electrodeposition (cathodic current efficiency, current density, and product deposition
rate) in electrolyte system M2WO4-M2W2O7-UO2WO4 (M = Li, Na, K, Cs) was studied in air. A conclusion was made that optimum electrodeposition and production of deposits not
contaminated with supporting electrolyte decomposition products need higher cathodic polarization close to the solvent decomposition
potentials and higher temperatures (up to 900°C). A melt based on K2WO4 was selected as the electrolyte providing satisfactory electrodeposition parameters of uranium dioxide with the composition
close to stoichiometric. 相似文献
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合成的3',6'-对戊酰硼荧光素是一种基于去保护机理的高灵敏H2O2荧光增强化合物, 能灵敏地检测出样品中H2O2的含量. 用IR, 1H NMR 对该探针的结构进行了表征, 并且讨论了反应时间、溶剂、碱对探针合成的影响. 研究了探针的最佳响应时间, 结果表明检测过程中反应的最佳时间为3 min. 该探针在2.3×10-12~2.0×10-8 mol/L H2O2溶液范围内呈荧光增强趋势, 检测下限为2.3×10-12 mol/L. 此探针重现性良好, 在血清中检测H2O2的回收率在93.9%~102.2%之间, 结果令人满意, 具有一定的实用价值. 相似文献
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Xiang Ying Chen 《Journal of solid state chemistry》2008,181(9):2127-2132
We described herein a facile solution-phase route to three nanocrystals of antimony oxychlorides and oxides (Sb4O5Cl2, Sb8O11Cl2, and Sb2O3), whose morphologies and phases were varied with the pH value of a reaction mixture or composition of a mixed solvent. In particular, the solvent composition controlled the selective preparation of cubic Sb2O3 (senarmontite) and orthorhombic Sb2O3 (valentinite). Both cubic and orthorhombic Sb2O3 samples exhibited strong emission properties. 相似文献
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Ibnelwaleed A. Hussein M. Sayem Mozumder Sk. Asrof Ali 《European Polymer Journal》2005,41(10):2472-2482
Rheological properties of hydrophobically modified copolymer of SO2, N,N-diallyl-N-carboethoxymethylammonium chloride and the hydrophobic monomer N,N-diallyl-N-octadecylammonium chloride were studied. The influence of hydrophobe content (HP) and polymer concentration was investigated. Polymers with HP content in the range 1.5-5% were examined and the concentration was varied in the range 2-5 wt%. Both dynamic and steady-shear experiments were performed in ARES rheometer. Copolymers were observed to exhibit typical viscoelastic behavior even with low HP content. Both the dynamic viscosity, η′ and storage modulus, G′, increase with the increase of both the polymer concentration and the HP content of the system. The viscosity of the high HP content polymer showed a strong shear dependency, while G′ was a weak function of frequency and gel-like behavior was observed. The zero-shear viscosity, η0, showed a strong concentration dependency (η0 ∼ ?α; 1.1 < α < 5.9). The concentration dependency of η0 suggests that intermolecular association is dominant in the high HP content polymer. Control of the HP content and polymer concentration of this class of polymers can lead to a wide range of interesting rheological properties. 相似文献
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用密度泛函理论研究了CF3SO3CF2CF3+F-的碳氧键断裂反应的机理. 首先, 用DFT方法优化了反应物、中间体、过渡态、产物的平衡构型, 分析了碳氧键断裂反应的势能面变化. 发现在SN2反应机理中, 除了S—O断裂SN2反应外, 引起C—O键断裂的同面进攻也是一个可能的反应途径. 理论计算表明, 最终反应的产物是受热力学控制的, S—O键的断裂绝对地优于C—O的断裂. 因此, C—O断裂的同面机理虽然是可能的, 但却难以被实验观察到. 本文还讨论了端基 —F3在同面SN2反应中的邻位效应, 以及基组对这个效应的影响. 相似文献
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Polyol-mediated solvothermal synthesis and luminescence properties of CeF3, and CeF3:Tb nanocrystals
Xuesong Qu Hyun Kyoung Yang Byung Kee Moon Jung Hyun Jeong Kwang Ho Kim 《Journal of solid state chemistry》2011,184(2):246-251
CeF3 and CeF3:Tb3+ nanocrystals were successfully synthesized through a facile and effective polyol-mediated route with ethylene glycol (EG) as solvent. Various experimental techniques including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and photoluminescence (PL) spectra as well as decay dynamics were used to characterize the samples. The results indicated that the content of NH4F and reactant concentrations were key factors in the product shape and size. Excessive NH4F was necessary for the formation of hexagonal nanoplates. The specific morphology of product can be controlled by changing the NH4F content and reactant concentrations. In addition, Tb3+ doped-CeF3 sample shows strong green emission centered at 544 nm corresponding to the 5D4-7F5 transition of Tb3+. Due to the decrease of nonradiative decay rate, the lifetime of 5D4 level of Tb3+ become longer gradually upon increasing the size of product. 相似文献
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Cationic polymerization of isobutylene (IB) in a mixture of methylene dichloride (CH2Cl2) and n-hexane (n-Hex) was conducted by using H2O as initiator, TiCl4 as co-initiator in the presence of strong external electron pair donor (ED), such as pyridine (Py), dimethylacetamide (DMA) or triethylamine (TEA). The effects of ED concentration, TiCl4 concentration, solvent polarity, polymerization temperature (T) and time on IB polymerization, molecular weight (MW) and molecular weight distribution (MWD, Mw/Mn) of polyisobutylene (PIB) products were investigated. The relative amount of polymer formed via uncontrolled initiation by conventional active species (I) decreased with increasing the solvent polarity, TiCl4 concentration and ED concentration in the polymerization. The desirable polymerization of IB with apparent absence of chain transfer reactions could be obtained by H2O/TiCl4 initiating system in the presence of ED under the appropriate reaction conditions. The external electron pair donors and TiCl4 did specially play important and effective roles on polymerization. 相似文献