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141.
Gottfried Lichti Brian S. Hawkett Robert G. Gilbert Donald H. Napper David F. Sangster 《Journal of polymer science. Part A, Polymer chemistry》1981,19(4):925-938
Data are presented on the time evolution of particle-size distributions (PSDs) in seeded and ab initio styrene emulsion polymerization systems. Initiation was by chemical reagent (potassium persulfate) or γ-radiation. The unswollen PSDs at various times during interval II of the polymerization were obtained by direct measurement of calibrated electron micrographs. Experimental results were fitted with the equations that describe the time evolution of an initial PSD. Analytic solutions to these equations that allow for entry, exit, and propagation of free radicals were obtained. The values of the rate coefficients for these processes used to fit the experimental data were in excellent agreement with those obtained from dilatometric kinetics experiments. 相似文献
142.
The new methylidene trinickel cluster complexes, [RCNi3(η5-C5H53] (R CMe3 or SiMe3) and [Me3SiCNi3(η5-C5H5)2(η5-C5H4CH2SiMe3)] have been isolated in low yield from reactions between nickelocene and the corresponding alkyllithium reagents, RCH2Li. The compounds [RCNi3(η5-C5H5)3] (R Ph, CMe3 or SiMe3) have also been obtained by treatment of the σ-alkylnickel complexes [(η5-C5H5)Ni(CH2R)(PPh3)] with n-BuLi in the presence of an excess of nickelocene, but under similar conditions [(η5-C5H5)Ni(CH2C1OH7-2)-(PPh3)] (where C1OH7-2 2-naphthyl) failed to give [2-C1OH7CNi3(η5-C5H5)3]. The attempted synthesis of [(η5-C5H5)Ni(CH2CCH)(PPh3)] from [(η5-C5H5)-NiBr(PPh3)] and CHCCH2MgBr gave only [(η5-C5H5)Ni(CCMe)(PPh3)] by an unusual rearrangement reaction. 相似文献
143.
The stabilities of different isomers of C60Brn have been calculated for n = 2 to 12. A general stereochemical pattern which emerges is the tendency to form strings created by the edge sharing of C6Br2 hexagonal faces. Stable structures are formed if these strings form loops, thereby eliminating string ends, which may involve the creation of C6Br3 hexagonal faces. A particularly stable structure is formed at C60Br6 in which the loop forms a C10Br6 fragment with a pentagonal pyramidal arrangement of six bromine atoms. Two isomers of C60Br12 are also particularly stable. One isomer contains two of these Br6 pentagonal pyramids on opposite sides of the molecule, and the other isomer contains a single large loop wrapped around the middle of the molecule. 相似文献
144.
The dynamic behaviour of [Pt(/gh3-allyl){P(cyclohexyl)3}2]+[PF6]- has been reinvestigated, and the earlier interpretation of restricted rotation about the Pt—P endorsed. The activation parameters were obtained. [Pt(/gh3-allyl)(PPri3)2]+[PF6]- behaves similarly, while it has not prove possible to stop the rotation in [Pt(/gh3-allyl){P(CH2Ph)3}2]+[PF6]-. 相似文献
145.
The products of hydrolysis of C60F48 (which contains six isolated double bonds) by either aq. acetone or aq. THF show that no more than twelve fluorines are replaced through nucleophilic substitution, as predicted by the recently identified S(N)2' mechanism. Subsequent HF elimination gives fragments containing a maximum of six epoxide oxygens. Calculated heats of formation of models for the possible initial hydroxy derivatives indicate that there is little energetic discrimination between them, so that a complex mixture is likely to be formed. Overall the data show that hydrolytic degradation of fluorofullerenes is less severe than believed previously, requires a specific motif, and explains the low susceptibility of C60F18 towards hydrolysis and the high stability of trannulenes. 相似文献
146.
[reaction: see text] A simple, efficient, and high-yielding synthesis of quinazolin-4-ylamine and thieno[3,2-d]pyrimidin-4-ylamine derivatives is reported under microwave irradiation conditions. Reaction conditions including temperature, solvent, and reaction time have been studied. An efficient parallel workup procedure was developed to generate a small library (23 compounds) in a short time period. 相似文献
147.
Dowding PJ Atkin R Vincent B Bouillot P 《Langmuir : the ACS journal of surfaces and colloids》2004,20(26):11374-11379
Microcapsules with an oil core surrounded by a polymeric shell have been prepared by the controlled phase separation of polymer dissolved within the oil droplets of an oil-in-water emulsion. The dispersed oil phase consists of the shell polymer (polystyrene), a good solvent for the polymer (dichloromethane), and a poor solvent for the polymer (typically hexadecane). Removal of the good solvent results in phase separation of the polymer within the oil droplets. If the three interfacial tensions between the core oil, the shell-forming polymer, and the continuous phase are of the required relative magnitudes, a polymer shell forms surrounding the poor solvent. A UV-responsive organic molecule was added to the oil phase, prior to emulsification, to investigate the release of a model active ingredient from the microcapsules. This molecule should be soluble in the organic core but also have some water solubility to provide a driving force for release into the continuous aqueous phase. As the release rate of the active ingredient is a function of the thickness of the polymeric shell, for controlled release applications, it is necessary to control this parameter. For the preparative method described here, the thickness of the shell formed is directly related to the mass of polymer dissolved in the oil phase. The rate of volatile solvent removal influences the porosity of the polymer shell. Rapid evaporation leads to cracks in the shell and a relatively fast release rate of the active ingredient. If a more gentle evaporation method is employed, the porosity of the polymer shell is decreased, resulting in a reduction in release rate. Cross-linking the polymer shell after capsule formation was also found to decrease both the release rate and the yield of the active ingredient. The nature of the oil core also affected the release yield. 相似文献
148.
Fry B Silva SR Kendall C Anderson RK 《Rapid communications in mass spectrometry : RCM》2002,16(9):854-858
Elemental analyzers have been successfully coupled to stable-isotope-ratio mass spectrometers for online measurements of the delta(34)S isotopic composition of plants, animals and soils. We found that the online technology for automated delta(34)S isotopic determinations did not yield reproducible oxygen isotopic compositions in the SO(2) produced, and as a result calculated delta(34)S values were often 1-3 per thousand too high versus their correct values, particularly for plant and animal samples with high C/S ratio. Here we provide empirical and analytical methods for correcting the S isotope values for oxygen isotope variations, and further detail a new SO(2)-SiO(2) buffering method that minimizes detrimental oxygen isotope variations in SO(2). 相似文献
149.
Dimitris K. Agrafiotis Brian Tansy Andrew Streitwieser 《Journal of computational chemistry》1990,11(9):1101-1110
Two new computational methods for the evaluation and partitioning of projected, planar, and averaged slab electron densities, implemented in the program PRODEN, are presented. The new algorithms for the projection, demarcation, and integration of electron densities are described and evaluated in terms of speed and numerical accuracy. Integrated Projected Populations are analyzed and some of the advantages and limitations of the methods are discussed. 相似文献
150.
The ab initio Neglect of Differential Diatomic Overlap (N.D.D.O.) method of Roby is tested numerically for an extensive series of molecules. Agreement with the full ab initio molecular orbital method is poor. Total energies are more negative and dipole moments are overestimated. The failings of the N.D.D.O. method are accounted for using multipole-multipole expansions. 相似文献