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Khalid Ibrahim Katariina Yliheikkilä Barbro Löfgren Markku Leskelä Jukka Seppälä 《European Polymer Journal》2004,40(6):1095-1104
Four tetradentate nitrogen ligands, viz. dichloro{[N,N′-diphenyl-N,N′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (1), {[N,N′-dioctyl-N,N′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (2), {[N,N′-dibenzyl-N,N′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (3), and (1R,2R)-(−)-N,N′-di(quinoline-2-methyl) di-iminocyclohexane (4), were investigated as novel complexing ligands in iron-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate where ethyl-2-bromoisobutyrate was the initiator in o-xylene at 90 °C. With ligands 1 and 2 the experimental molecular weights increased gradually with monomer conversion. High to moderate conversions (87%, 43%) were obtained in relatively short times (90 min for 1 and 30 min for 2), which indicates an efficient catalyst system, but after these times a dramatic increase in viscosity of the polymerization medium led to loss of control. It is noteworthy that polymerization proceeded in a controlled manner with ligand 1, which has two rather bulky substituents on the N-atom. Such bulky ligands did not work for a copper-based system, where they led to excessive terminations or other side reactions. When the bulkiness of the substituents was significantly increased, as in ligand 3, a decrease in polymerization rate and loss of control occurred. Ligand 4 was less efficient than the other ligands, probably because the ethylene bridge was replaced by cyclohexane bridge. 相似文献
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F. G. H. Van Wijk C. B. Beijer P. Gast T. J. Schaafsma 《Photochemistry and photobiology》1987,46(6):1015-1019
The electron spin polarization (ESP) pattern of the donor-triplet state (PR ) of reaction centers (RC's) of the purple bacterium Rhodobacter (formerly Rhodopseudomonas) sphaeroides R-26 was investigated. δm =±1 triplet EPR spectra were recorded of unmodified RC's as well as of RC's from which Fe2+ or ubiquinone was removed, or ubiquinone was substituted by menaquinone.
The relative amplitude of the Y peaks in the triplet EPR powder spectrum of PR decreases when the temperature is increased from 8 K to 100 K in RC's with an intact quinone-iron complex. This decrease is more pronounced when the primary ubiquinone is substituted by menaquinone. These observations provide further support for the hypothesis that the observed lineshape of the PR triplet state EPR spectrum reflects the presence of a third electron spin, magnetically coupled to I- in the P+ I- radical pair, as suggested by Van Wijk et al. (1986) (Photobiochem. Photobiophys . 11, 95–100). Our observations suggest that this phenomenon may be general in purple bacteria. 相似文献
The relative amplitude of the Y peaks in the triplet EPR powder spectrum of P
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Tanja Seraidaris Arto Puranen Mikko Karesoja Barbro Lfgren Timo Repo Markku Leskel Jukka Seppl 《Journal of polymer science. Part A, Polymer chemistry》2006,44(16):4743-4751
Elastic polypropene has gained growing industrial and academic interest as a thermoplastic elastomer. In this study, “rac”‐ and “meso”‐dimethylsilyl(3‐benzylindenyl)(2‐methylindenyl)hafnium dichloride complexes (Hfr and Hfm, respectively), activated with [NHMe2Ph][B(C6F5)4]/triisobutyl aluminum, were used in propene polymerization. Using these catalyst systems, we obtained polymers with high molar masses, up to 550 kg/mol, and moderate isotacticities between 34 and 52%. By varying the polymerization conditions, we could modify the polymer microstructure and molar mass. 13C NMR was used to calculate the polymer pentad sequence distributions. The crystalline parts of the polymers were analyzed with the differential scanning calorimetry successive self‐nucleation and annealing (SSA) technique. The SSA thermograms revealed that Hfr produced polypropene with a more uniform lamellar structure than Hfm. The mechanical properties were tested with dynamic mechanical analysis creep‐recovery tests. In the series, the polymers with the lowest isotacticities and therefore lowest crystallinities showed the best elastic properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4743–4751, 2006 相似文献
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Esa Kokko Anneli Malmberg Petri Lehmus Barbro Lfgren Jukka V. Seppl 《Journal of polymer science. Part A, Polymer chemistry》2000,38(2):376-388
A study was made on the effects of polymerization conditions on the long‐chain branching, molecular weight, and end‐group types of polyethene produced with the metallocene‐catalyst systems Et[Ind]2ZrCl2/MAO, Et[IndH4]2ZrCl2/MAO, and (n‐BuCp)2ZrCl2/MAO. Long‐chain branching in the polyethenes, as measured by dynamic rheometry, depended heavily on the catalyst and polymerization conditions. In a semibatch flow reactor, the level of branching in the polyethenes produced with Et[Ind]2ZrCl2/MAO increased as the ethene concentration decreased or the polymerization time increased. The introduction of hydrogen or comonomer suppressed branching. Under similar polymerization conditions, the two other catalyst systems, (n‐BuCp)2ZrCl2/MAO and Et[IndH4]2ZrCl2/MAO, produced linear or only slightly branched polyethene. On the basis of an end‐group analysis by FTIR and molecular weight analysis by GPC, we concluded that a chain transfer to ethene was the prevailing termination mechanism with Et[Ind]2ZrCl2/MAO at 80 °C in toluene. For the other catalyst systems, β‐H elimination dominated at low ethene concentrations. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 376–388, 2000 相似文献
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A Nafion coating is applied on voltammetric carbon fibre electrodes. This treatment lowered the sensitivity to ascorbate and 3,4-dihydroxyphenylacetic acid (DOPAC), and increased that for dopamine. Electrochemical oxidation with a 70-Hz, 3-V, anodic triangular-wave voltage was used for pretreatment before the Nafion coating. The inclusion of copper ions in the Nafion film further decreased the sensitivity to ascorbic acid, but did not significantly affect to dopamine or DOPAC. In-vitro equilibration with a buffer of appropriate copper concentration is recommended for pretreatment of carbon fibre electrodes before their use in in-vivo voltammetry. 相似文献
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Florian Umstätter Dr. Cornelius Domhan Dr. Tobias Hertlein Priv.-Doz. Dr. Knut Ohlsen Eric Mühlberg Dr. Christian Kleist Dr. Stefan Zimmermann Dr. Barbro Beijer Dr. Karel D. Klika Prof. Dr. Uwe Haberkorn Prof. Dr. Walter Mier Dr. Philipp Uhl 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):8908-8912
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