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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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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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Nilsson J Carlberg J Abrahamsson P Hulthe G Persson BA Karlberg AT 《Rapid communications in mass spectrometry : RCM》2008,22(22):3593-3598
Hydroperoxides formed by autoxidation of common fragrance terpenes are strong allergens and known to cause allergic contact dermatitis (ACD), a common skin disease caused by low molecular weight chemicals. Until now, no suitable methods for chemical analyses of monoterpene hydroperoxides have been available. Their thermolability prohibits the use of gas chromatography and their low UV-absorption properties do not promote sensitive analytical methods by liquid chromatography based on UV detection. In our study, we have investigated different liquid chromatography/mass spectrometry (LC/MS) ionization techniques, electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photoionization (APPI), for detection of hydroperoxides from linalool and limonene.Flow injection analysis was used to evaluate the three different techniques to ionize the monoterpene hydroperoxides, linalool hydroperoxide and limonene hydroperoxide, by estimating the signal efficacy under experimental conditions for positive and negative ionization modes. The intensities for the species [M+H]+ and [M+H-H2O]+ in positive ionization mode and [M-H]- and [M-H-H2O]- in negative ionization mode were monitored. It was demonstrated that the mobile phase composition and instrumental parameters have major influences on the ionization efficiency of these compounds. ESI and APCI were both found to be appropriate as ionization techniques for detection of the two hydroperoxides. However, APPI was less suitable as ionization technique for the investigated hydroperoxides. 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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Anne-Marja Uusitalo Tuula T. Pakkanen Minna Krger-Laukkanen Lauri Niinist Kimmo Hakala Santeri Paavola Barbro Lfgren 《Journal of molecular catalysis. A, Chemical》2000,160(2):343-356
Heterogeneous metallocene catalysts were prepared by adsorbing rac-Et(Ind)2ZrCl2 on a modified silica surface in solution. The modification of silica was conducted in gas phase with atomic layer chemical vapor deposition (ALCVD) technique, where the silica, preheated at either 350 or 600°C, was allowed to react with vaporized trimethylaluminum (TMA) at 250°C. Modified carriers and heterogeneous catalysts were characterized with FTIR, 1H MAS (magic-angle spinning) NMR, 13C, and 29Si CP (cross-polarization) MAS NMR spectroscopies and elemental analyses. In the reaction of TMA with silica, a saturated surface was formed consisting of different (---O)4−nSi(CH3)n (n=1, 2 or 3) and ---AlCH3 groups. The ratio of ---SiMe to ---AlMe groups was approximately 1.5 in the TMA/SiO2 carriers. When the metallocene was adsorbed onto the carrier it seemed to react with the surface ---AlCH3 groups and possibly ---ZrCH3 groups were formed. Heterogeneous catalysts were tested in the polymerization of ethylene and propylene in the presence of methylalumoxane (MAO). And they produced similar polymer as the homogeneous rac-Et(Ind)2ZrCl2 catalyst, but with lower activity. A catalyst with the best activity was achieved from silica that was preheated at 600°C. Moreover, leaching of catalyst was examined whereupon a part of zirconium was observed to desorb from the carrier. 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