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51.
Brigitte Voit Sven Fleischmann Hartmut Komber Arnulf Scheel Katrin Stumpe 《Macromolecular Symposia》2007,254(1):16-24
Summery: The potential of cycloaddition (CA) reactions for the synthesis of dendritic polymers is pointed out. The [4 + 2] Diels Alder cycloaddition as well as 1,3-dipolar CA reactions including “click chemistry” are addressed, and the advantages of these reactions like high selectivity, thus high tolerance towards additional functionalities, high yields and synthesis under mild reaction conditions are highlighted. New perfectly branched dendrimers as well as hyperbranched polymers have been prepared and modified using the 1,3-dipolar cycloaddition reaction of azines with alkynes. The 1,3-dipolar CA reaction of bisazine with maleimides results in hyperbranched and thus, irregular and broadly distributed polymers though with a degree of branching of 100% due to special intermediate formation. The [4 + 2] Diels Alder cycloaddition was successfully applied for the synthesis of highly branched polyphenylene structures using the AB2 + AB and the A2 + B3 approach. CA reactions are also very suitable for highly efficient polymer analogous reactions and thus, they can also be used to prepare complex polymer architectures like dendronized polymers. 相似文献
52.
Wuye Ouyang Dietmar Appelhans Brigitte Voit Martin Muller 《Macromolecular Symposia》2007,254(1):180-187
Summary: Two chiral polyelectrolyte multilayers (PEM) composed of poly(L-lysine) (PLL) and poly(vinylsulfate) (PVS) as well as poly(ethyleneimine-maltose) (PEI-m) and poly(vinylsulfate) and a nonchiral PEM composed of poly(ethyleneimine) (PEI) and poly(vinylsulfate) were deposited on a silica surface using the layer by layer method. For both PEM enantiospecific interaction towards one enantiomer of either L-/D- glutamic acid (L-/D-GLU) or L-/D-ascorbic acid (L-/D-ASC), respectively, was checked under variation of the concentration. Both deposition and enantiospecific interaction were studied by attenuated total reflection Fourier transform (ATR-FTIR) spectroscopy. Preliminary results show a significant enantiospecific preference of D- GLU over L-GLU at PEM of PLL/PVS and of D-ASC over L-ASC at PEM of PEI-m/PVS and no such preference for nonchiral PEM of PEI/PVS. PEM of PLL/PVS shows higher enantiospecifity with increasing L-/D-GLU concentration. 相似文献
53.
Dietmar Appelhans Hartmut Komber Ralf Kirchner Jürgen Seidel Chih‐Feng Huang Dieter Voigt Dirk Kuckling Feng‐Chih Chang Brigitte Voit 《Macromolecular rapid communications》2005,26(8):586-591
Summary: Polypeptide‐shelled poly(propylene imine) dendrimers were realized by ring‐opening polymerization of α‐amino acid N‐carboxyanhydrides, initiated by dendrimers as core molecules. Polypeptides with 2nd generation core were used as model compounds to investigate interior complexes between metal ion and surface‐modified dendrimers. Micro‐calorimetric measurements outlined the formation of approximate 1:1 complexes between CuII and polypeptide‐shelled dendrimers and the influence of polypeptide chain compositions on differential molar heats of complexation.
54.
Sinusoidal intensity oscillations of the phase conjugated wave reflected from a self-pumped photorefractive BaTiO3 crystal have been observed. The oscillation amplitude is shown to be increased by providing optical feedback of the light scattered during grating formation. The oscillation frequency ? can be tuned from 0.024 Hz to 2 Hz by changing the light intensity I0 of the object beam from 0.7 W/cm2 to 100 W/cm2. A power law ? ∝ Iβ0 ∝ σ with β = 0.89 was observed over this range of intensities (σ = photoconductivity). Transitions to a chaotically oscillating or a stable reflecting state have been observed at higher power levels or with increased optical feedback. An additional pump beam near the entrance face of the signal beam can decrease the build-up time for the self-pumping process by a factor of five or more. 相似文献
55.
56.
C. Voit 《Fresenius' Journal of Analytical Chemistry》1876,15(1):469-472
Ohne Zusammenfassung 相似文献
57.
E. I. Voit A. V. Voit V. Ya. Kavun V. I. Sergienko 《Journal of Structural Chemistry》2004,45(4):610-616
A number of fluorozirconate clusters serving as structural models for K2ZrF6 and (NH4)2ZrF6 crystals were investigated by the Hartree-Fock ab initio method. Based on the results of quantum-chemical calculations it is shown that the differences in the structure of these compounds and in the behavior of the temperature dependence of the second moment of the 19F NMR spectra are due to differences in the binding between the cation and anion sublattices. A mechanism responsible for ionic mobility is suggested.Original Russian Text Copyright © 2004 by E. I. Voit, A. V. Voit, V. Ya. Kavun, and V. I. SergienkoTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 644–650, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date. 相似文献
58.
59.
Michael Voit 《manuscripta mathematica》1991,72(1):141-153
We show that the support of the Fourier transform of a positive, positive definite measure on a commutative hypergroupK contains a positive character. This generalizes the known fact that the support of the Plancherel measure π contains a positive
character (which in general is not the identity character1). It follows that
contains a positive character for
whenever a dual convolution exists. In particular, if1∈supp π, then1 is this character. We also give some further general results about the support of dual convolution products in terms ofsupp π. Some examples associated with Gelfand pairs and, in particular, non-compact Riemannian symmetric spaces of rank 1 are
discussed. 相似文献
60.