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951.
952.
Markus Klapper Yong-Jun Jang Kirsten Bieber Tanja Nemnich Nikolay Nenov Klaus Müllen 《Macromolecular Symposia》2004,213(1):131-146
Nano-sized latex particles as organic supports for metallocenes applied in olefin polymerizations are introduced. The particles are functionalized with nucleophilic surfaces such as polyethylenoxide (PEO), polypropyleneoxide (PPO) or pyridine units allowing an immobilization of the metallocene catalysts via a non-covalent immobilization process. The latices are obtained by emulsion or miniemulsion polymerization with styrene, divinylbenzene as the crosslinker, and either PEO or PPO functionalized styrene or 4-vinylpyridine for surface functionalization. The supported catalysts, e.g. [Me2Si(2MeBenzInd)2ZrCl2/MAO] on PPO containing latices or Cp2ZrMe2/([Ph3C][B(C6F5)4]) on pyridine functionalized materials were tested in ethylene polymerizations. Remarkably, high activities and excellent product morphologies were obtained. The influence of the degree of surface functionalization on activity and productivity was investigated. Furthermore, the fragmentation of the catalyst was studied by electron microscopy using bismuth-labeled latex particles or by fluorescence and confocal fluorescence microscopy using dye-labeled supports. Finally, a self-immobilizing catalyst/monomer system is presented. It is demonstrated that by using PEO-functionalized olefins, the metallocenes were immobilized on the monomers. Subjecting these mixtures to an ethylene copolymerization, again high activities and productivities as well as polyolefin beads with high bulk densities are observed, indicating that an extra supporting process for controlling the product size and shape of the polyolefins is not necessary for these monomers. 相似文献
953.
Nikolay A. Platé Arkady D. Litmanovich Yaroslav V. Kudryavtsev Elena N. Govorun 《Macromolecular Symposia》2003,191(1):11-20
Various effects produced by copolymers in polymer blends are discussed, with an emphasis on the role of interchain interactions. Simple theoretical models are considered to study the following problems: the interplay of diffusion and macromolecular reaction in compatible and incompatible blends, the stabilizing effect of premade diblock copolymer on the system of minor phase particles in incompatible blends, the kinetics of transesterification in a homogeneous blend. The effect of diblock copolymer on the Ostwald ripening in a polymer blend is stated in more details; the possibility of narrowing the size distribution of minor phase particles is predicted. 相似文献
954.
Job J. C. Struijs Valery Muravev Marcel A. Verheijen Emiel J. M. Hensen Nikolay Kosinov 《Angewandte Chemie (International ed. in English)》2023,62(5):e202214864
The direct catalytic conversion of atmospheric CO2 to valuable chemicals is a promising solution to avert negative consequences of rising CO2 concentration. However, heterogeneous catalysts efficient at low partial pressures of CO2 still need to be developed. Here, we explore Co/CeO2 as a catalyst for the methanation of diluted CO2 streams. This material displays an excellent performance at reaction temperatures as low as 175 °C and CO2 partial pressures as low as 0.4 mbar (the atmospheric CO2 concentration). To gain mechanistic understanding of this unusual activity, we employed in situ X-ray photoelectron spectroscopy and operando infrared spectroscopy. The higher surface concentration and reactivity of formates and carbonyls—key reaction intermediates—explain the superior activity of Co/CeO2 as compared to a conventional Co/SiO2 catalyst. This work emphasizes the catalytic role of the cobalt-ceria interface and will aid in developing more efficient CO2 hydrogenation catalysts. 相似文献
955.
Natalya Permyakova Tatyana Zheltonozhskaya Nikolay Strilchyk Nina Zagdanskaya Lesya Momot Vladimir Syromyatnikov 《Macromolecular Symposia》2003,203(1):247-258
Complex formation in the model three-component system, including polymer-polymer complex of poly(styrene-alt-maleic acid) (PSMA) and poly(ethylene oxide) (PEO), and also silica sol (SiO2) in aqueous solution as a function of molecular weight of PEO and the order of component mixing, were investigated. The degree of binding of PSMA links with PEO and SiO2 as well as the Gibbs energy of formation of the polymer-polymer complex and polymer-colloid complexes were defined. It was shown that the main factor of stabilization of the structure is hydrogen bonds. The conditions of three-component polymer-colloid system are practically independent of the order of component mixing. The spontaneous formation of polymer-colloid complexes between chemically complementary polymers and small dispersed particles is considered as the main reason for the abnormally high binding ability of colloid particles to the polymer-polymer complex. 相似文献
956.
Freak or rogue waves on the ocean seemingly appear from nowhere, cause severe damage to ships and offshore structures due to their large crest heights, and disappear at once. Since the Draupner wave measured on New Year's day 1995 finally confirmed the existence of freak waves, different models were developed to describe them. One deterministic model to investigate their occurrence is the nonlinear Schrödinger equation (NLS) describing the nonlinear evolution of wave train envelopes. Due to the modulation instability, also referred to as Benjamin-Feir instability, strong spatial localization of wave amplitude may arise and breather type solutions are hypothesized to form the dynamical back-bone of rogue waves. To test this hypothesis, breather type solutions of the NLS are compared to two extreme wave records: the Draupner wave recorded in central North Sea and the Yura wave recorded in the Sea of Japan. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献