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91.
A simple means is deduced for determining conditions for secondary particle formation in emulsion polymerization systems in systems where the amount of added surfactant is below the cmc. A new radical formed from initiator in the aqueous phase will undergo some polymerization with aqueous-phase monomer, but must have three possible eventual fates: aqueous-phase termination, entry into a preexisting particle, or creation of a new particle. The means for determining the onset and extent of secondary nucleation is to modify HUFT theory to take into account a successful model for entry [ Macromolecules, 24, 1629 (1991)] which states that entry occurs if and only if the aqueous-phase radical has achieved a critical degree of polymerization z. Particle formation below the cmc is by homogeneous/coagulative nucleation which (if coagulation is ignored) gives an upper bound to the rate of formation of precursor particles; these are of a degree of polymerization Jcrit > z. The resulting equations are readily solved, and require only a knowledge of the aqueous-phase propagation and termination rate coefficients (the latter is very high: ca. 109 dm3 mol−1 s−1 for termination between the very small radicals), z and jcrit. Easily applied means are given for estimating all these quantities. The treatment gives good accord with experimentally observed conditions for the onset of secondary nucleation in low-surfactant systems (including taking in situ micellization into account). 相似文献
92.
Imine 7 of 1,4-cyclohexanedione mono-ethylene ketal 6 was reacted with maleic anhydride, affording the cyclized adduct 8. Methyl esterification of 8, accompanied by transacetalization, led to the dihydrooxindole derivative 10. Aromatization of 10 was then accomplished with POCl(3), leading directly to the key-intermediate title compound 11 in 74% yield from ketone 6. Serotonin, melatonin, and bufotenin were then obtained by standard reactions. 相似文献
93.
Synthesis of grafting silane on a hydro soluble cellulose ether (HPMC) was described. In alkaline medium, this derivate is under gel form. With a decrease of the pH, a self-hardening occurs due to the silanol condensation. For potential biomedical use, we described the silated-HPMC synthesis, the gel behavior after steam sterilization and the parameters of the silanol condensation i.e. pH, silane percentage and temperature. Minimum kinetic of the condensation was observed for pH between 5.5 and 6.5. So temperature catalyzed the reaction and the self-hardening speed was increased by silane percentage. 相似文献
94.
Noncovalent engineering of carbon nanotube surfaces by rigid,functional conjugated polymers 总被引:8,自引:0,他引:8
Chen J Liu H Weimer WA Halls MD Waldeck DH Walker GC 《Journal of the American Chemical Society》2002,124(31):9034-9035
We report a new nonwrapping approach to noncovalent engineering of carbon nanotube surfaces by short, rigid functional conjugated polymers, poly(aryleneethynylene)s. Our technique not only enables the dissolution of various types of carbon nanotubes in organic solvents, which represents the first example of solubilization of carbon nanotubes via pi-stacking without polymer wrapping, but could also introduce numerous neutral and ionic functional groups onto the carbon nanotube surfaces. 相似文献
95.
John E. Gilbert Andrea R. Nahmod 《Transactions of the American Mathematical Society》1999,351(8):3267-3300
The study of bilinear operators associated to a class of non-smooth symbols can be reduced to ther study of certain special bilinear cone operators to which a time frequency analysis using smooth wave-packets is performed. In this paper we prove that when smooth wave-packets are replaced by Walsh wave-packets the corresponding discrete Walsh model for the cone operators is not only -bounded, as Thiele has shown in his thesis for the Walsh model corresponding to the bilinear Hilbert transform, but actually improves regularity as it maps into a Hardy space. The same result is expected to hold for the special bilinear cone operators.
96.
Gilbert Greefrath 《ZDM》1999,31(3):91
Information
Allgemeine Mathematik: Mathematik und Realit?t Darmstadt, 29.9–1.10.1999 相似文献97.
B. Boffey Francisco Ramón Fernández García Gilbert Laporte Juan A. Mesa Blas Pelegrín Pelegrín 《TOP》1995,3(2):167-220
Summary Many network routing problems, particularly where the transportation of hazardous materials is involved, are multiobjective
in nature; that is, it is desired to optimise not only physical path length but other features as well. Several such problems
are defined here and a general framework for multiobjective routing problems is proposed. The notion of “efficient solution”
is defined and it is demonstrated, by means of an example, that a problem may have very many solutions which are efficient.
Next, potentially useful solution methods for multiobjective routing problems are discussed with emphasis being placed on
the use of shortest/k-shortest path techniques. Finally, some directions for possible further research are indicated.
Invited by B. Pelegrin 相似文献
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