Recalculation of monomer reactivity considering the effect of monomer partitioning in microemulsion

From the copolymerisation data for the microemulsion polymerisation of both partially water soluble monomers ethylacrylate (EA)-methylmethacrylate (MMA) the concentration of the monomer at the polymerisation loci was calculated. While the reported copolymerisation data for the microemulsion copolymerisation of styrene (Sty)-methylacrylate (MA), monomer pair with different solubility and polarity and Sty-butylacrylate (BA), monomer pair with similar solubility and different polarity was used to calculate the monomer concentration at loci. It was inferred from the non-constancy of f^′_A/f_A and f^′_B/f_B ratio that the preferential site of polymerisation might be the emulsifier layer in case of Sty-MA and Sty-BA. While, based on the monomer fraction in the copolymer and the constancy of f^′_A/f_A and f^′_B/f_B it was concluded that microemulsion polymerisation for monomer pair EA-MMA, having similar solubility and polarity, conforms more to bulk polymerisation, where there is no preferential site of polymerisation. The loci concentration rather than feed value was used to recalculate the reactivity at the site of polymerisation. Also the loci concentration was calculated assuming their sum at the polymerisation site equal to unity.     

疏水-亲脂相互作用对反应活性的影响 13: 羧甲基糖淀粉钠催化酯水解的溶剂效应

在H2O, Mo2SO-H2O, Dioxane-H2O, t-BuOH-H2O体系中, 羧甲基糖淀粉钠(NaCMA)对不同链长的羧酸对硝基苯酚酯的水解有显著的加速作用, 并表明, 即使在受物发生部分簇集的情况下, NaCMA的催化作用仍呈饱和动力学。讨论了有机溶剂、受物的链长、受物的聚集状态对包结络合物解离常数Kd及催化酯水解速率常数kc的影响。实验结果表明, NaCMA-受物包结络合物在纯水中最稳定, 有机溶剂的存在不同程度地降低了NaCMA催化酯水解的能力和包结络合物的稳定性。     

The effect of an activation solution with siliceous species on the chemical reactivity and mechanical properties of geopolymers

Precursors are critical parameters in geopolymerization mechanisms because they govern the reaction kinetics as well as the working properties of the final materials. This study focuses on the effect of alkaline solutions on geopolymer formation. Toward this end, several geopolymer samples were synthesized from the same metakaolin and various alkaline solutions. First, the solutions were characterized by thermogravimetric analysis as well as DTA–TGA, infrared spectroscopy, and MAS-NMR spectrometry. The structural evolution of the formed geopolymers was investigated using infrared spectroscopy. The measurement of mechanical strength was tested by compression. The results provide evidence of relationships between the chemical composition, the extent of depolymerization of the alkaline solutions, the kinetics of Si–O–Si bond substitution by Si–O–Al and the compressive strength. For a given aluminosilicate source, the nature and the quantity of siliceous species in the activation solution appear to lead to variation in the reactivity and, consequently, to the formation of various networks that control the kinetics of formation of geopolymers and their mechanical properties.

     

疏水-亲脂相互作用对化学反应性的影响 7: 十四元和十八元环的邻基参与

本工作研究了不同链长的ω-取代羧酸对硝基苯酯p-NO2-C6H4OCO(CH2)n-1Y(简称n-Y,n=17,13,11;Y=SH,H,OH,Br和SCH3)在Me2SO-H2O溶剂体系(有机溶剂体积组成分数φ=0.40,0.45,0.50,0.55)中的水解动力学,观察到疏水-亲脂作用影响下,由于13-SH和17-SH长链分子自身绕曲,可以实现十四元环和十八元环的大环邻基参与,至于11-SH的水解,则观察不到十二元环的邻基参与.因此,这些受物的邻基助效确与链长有关.溶剂组成对此现象也有影响.     

Quantum chemical contributions on the reactivity of solids

The concept of reactivity is reviewed. Various reactivity indices are discussed. Different methods for the simulation of solids are systematically described. Applications for the reactivity of solids can be subdivided into three categories: surfaces, interfaces and bulk. Examples for the categories are presented with a special emphasis on diffusion processes in the bulk.     

Effect of soot microstructure on its ozonization reactivity

Large uncertainty among the measured uptake coefficients of O(3) on soot highlights the importance of the sources and chemical structures of soot samples in this reaction. Soot samples with different microstructures were prepared by combusting n-hexane under controlled conditions. Their reactivities to O(3) were further investigated using in situ Raman spectroscopy. The fuel∕oxygen ratio in the combustion experiments not only affected the diameter of the primary particles, but also influenced the micro-chemical structure of soot. Average diameters of soot particles decreased with the decreasing fuel∕oxygen ratio. Compared to the "fuel-rich" flame soot, the "fuel-lean" flame soot showed lower structural uniformity with higher disordered carbon content at the graphene layer edges (D1 band) and the surface graphene layers (D2 band) and the amorphous carbon content (D3 band). This disordered carbon was identified as the reactive component for the ozonization of both the "fuel-rich" and "fuel-lean" flame soot samples. The kinetics study demonstrated that the disordered carbon at the surface graphene layers was more active than that at the graphene layer edges in one sample, and the reactivity of these two microstructures types to O(3) in the "fuel-rich" flame soot was higher than that in the "fuel-lean" flame soot.     

The effect of substitution on the properties of a chemical group

The effect of the substituent R(R = F, OH, NH₂, CH₃) on the electron distribution of the C=C group of ethylene and acrylonitrile may be fairly well represented in terms of classical interactions between the and components of this group and the molecular remainder. A distinction between direct and indirect effects is made, and an estimate of the relative importance of conjugative versus inductive effects is done.This analysis has been performed on a set of 22 SCF wavefunctions calculated with the 4-31G basis set.     

Ligand field effect at oxide-metal interface on the chemical reactivity of ultrathin oxide film surface

Ultrathin oxide film is currently one of the paramount candidates for a heterogeneous catalyst because it provides an additional dimension, i.e., film thickness, to control chemical reactivity. Here, we demonstrate that the chemical reactivity of ultrathin MgO film grown on Ag(100) substrate for the dissociation of individual water molecules can be systematically controlled by interface dopants over the film thickness. Density functional theory calculations revealed that adhesion at the oxide-metal interface can be addressed by the ligand field effect and is linearly correlated with the chemical reactivity of the oxide film. In addition, our results indicate that the concentration of dopant at the interface can be controlled by tuning the drawing effect of oxide film. Our study provides not only profound insight into chemical reactivity control of ultrathin oxide film supported by a metal substrate but also an impetus for investigating ultrathin oxide films for a wider range of applications.     

The effect of plasticization on craze microstructure

The structure of crazes in plasticized polystyrene has been studied by means of small-angle x-ray scattering and optical interference microscopy. Addition of plasticizer causes a rapid increase in the mean fibril diameter D and a slow decrease in the craze fibril volume fraction v_f. The crazing stress σ_c was also measured and it was found that the product D σ_c is independent of plasticizer concentration. These results are shown to be consistent with the entanglement model for controlling v_f and the meniscus instability model of craze thickness growth.     

The effect of hydrophobic-lipophilic interactions on chemical reactivity. 9. Putting the spotlight on lipophilic forces in solvent-effect studies

The hydrolytic rate constants of thep-nitrophenyl esters of acetic, octanoic, dodecanoic and hexadecanoic acids in six aquiorgano binary mixtures of graded compositions at various initial substrate concentrations were measured and discussed in terms of the hydrophobic-lipophilic interactions between the substrate molecules, and the organic cosolvents which were MeOH, Me₂SO, 1, 4-dioxane, 1,2-dimethoxyethane,n-propanol andt-butanol. The accelerating or retarding effects of the organic cosolvents on the rate constants of hydrolysis were found to be directly related to the lipophilicities of the solvents which were changed either by changing the content (ϕ) or the nature of the organic cosolvent. The classification or ordering of the six solvents on the basis of their solvent effects were found to conform to the lipophilicity order derived from Rekker's Σf values. The results support the proposition that lipophilic interactions can play an important role in solvent effects of aqueous binaries.     

The effect of hydrophobic-lipophilic interactions on chemical reactivity: 7. Fourteen and eighteen-membered-ring neighboring group participations

Hydrolytic rate constants of p-nitrophenyl esters of ω-substituted straight chain acids with various chain lengths were measured in Φ=0.40, 0.45, 0.50, 0.55 Me₂SO-H₂O mixtures. It has been demonstrated that for the long-chain substrates 13-SH and 17-SH hydrophobic-lipophilic forces can bring about 14-membered-ring and 18-membered-ring “neighboring group” participations in aggregating solvents. Twelve-membered-ring participation has not been observed for 11-SH, indicating that tendencies towards self-coiling and aggregating parallel each other.     

A nanoreactor for tuning the chemical reactivity of a solute

Present results demonstrate that the redox potential and hence the chemical reactivity of a solute dissolved in a polymer-surfactant supramolecular assembly, considered as a nanoreactor, can be tuned substantially by changing the composition of the supramolecular assembly. It is understood from detailed study that, on changing the polymer-surfactant composition of the supramolecular assembly, the probe undergoes a change in its location in these nanoreactors and accordingly its physical and chemical properties can be modulated.     

热处理对煤焦反应性及微观结构的影响

用热天平和XRD考察了热处理对二种煤(河北蔚县褐煤、四川湔江烟煤)镜质组半焦微观结构和反应活性的影响。TGA结果表明，热处理温度增加，蔚县煤镜质组(YXV)与湔江煤镜质组(JJV)焦炭的反应性降低；YXV焦炭的反应性随着热处理时间的增加而急剧下降，但一定热处理时间(60 min)后，其下降趋势变缓；热处理时间对JJV焦炭的影响较小。XRD结果表明，在热处理温度为900 ℃，初焦热处理时间为60 min时，YXV焦炭晶格结构发生明显改变，900 ℃以上，YXV焦炭芳香堆垛高度Lc随着热处理时间的增加而增加；热处理时间对JJV焦炭的影响不如YXV显著，而只有在较高的热处理温度(1 200 ℃)下，碳的微观结构才出现明显的有序化。热处理导致的焦炭微观碳结构趋于有序化是焦炭反应性下降的主要原因。     

The mechanism of the distant substituent effect on molecule reactivity

The effect of distant polar substituents on the reaction mechanism of some chemical reactions is considered. It has been shown that the traditional approach, based on transferring the substituent action to the reaction centre along the chain of bonds connecting them and leading to a significant change in electronic density at the reaction centre, is wrong. The role of a polar substituent consists of changing, sometimes dramatically, the electrostatic potential character around the molecule, particularly in the space near the reaction centre.     

The effect of aryl substituents on arylcarbene reactivity

Substituted (p-MeO, p-Me, H, p-Cl, p-Br, m-Br, m-MeO, 3,4-Cl₂, p-CO₂Me, m-CN and p-CN) monophenylcarbenes are generated in a binary mixture of substrates (methanol, cis-4-methyl-2-pentene and cyclohexane) and the relative rate of O—H insertion into methanol to stereospecific cyclopropanation of the olefin to C—H insertion into cyclohexane are calculated from the ratios of products and substrates. It is found (i) that the reactivities of the substrates decrease in the order of methanol, olefin and cyclohexane and (ii) that electron-donating substituents generally lead to reaction with the more reactive substrates while the reaction with the less reactive substrates is favoured in the case of electron-withdrawing substituents. These results are interpreted in terms of the change in the electrophilicity of the singlet arylcarbene by the substituents rather than the change in the singlet-triplet equilibrium.     

Studies on high chemical reactivity of nano-NaH

A comparison between the initial reaction rates of nanometric and commercial NaH has been studied in four test reactions: 1) hydrogenolysis of chlorobenzene; 2) selective reduction of cinnamaldehyde to cinnamyl alcohol; 3) metallation of dimethyl sulfoxide; and 4) catalytic hydrogenation of olefins. The experimental results indicate that when NaH is used as a chemical reagent in the first three reactions, the initial reaction rates of nano-NaH is 230, 120 and 110 times higher than those of the commercial ones respectively, and it is in agreement with the difference in specific surface areas between these two forms of NaH. When NaH is used as a catalyst component together with Cp₂TiCl₂ in the fourth reaction, catalyst with nano-NaH gives extremely high activity in the hydrogenation of olefins, while the one with commercial NaH gives no activity at all even if a large amount of the commercial NaH is used to make the total surface area equivalent to that of nano-NaH. Thus, it is evident that although large specific surface area is important for nano-NaH to be used as a catalyst component, high surface energy with surface defects seems to be more important. The large specific surface and the activated surface of nano-NaH with high surface energy should be the main factors for their extremely high chemical reactivity, while whether the former or the latter one plays a leading role depends on the type of reactions involved. __________ Translated from Chinese Journal of Applied Chemistry, 2007, 24(1): 21–24 [译自: 应用化学]