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831.
Łukasz Byczyński 《Journal of Thermal Analysis and Calorimetry》2013,114(1):397-408
Poly(urethane-dimethylsiloxane) (PU-PDMS) copolymers with 4,4′-methylenebis(cyclohexyl isocyanate), different polyethers i.e., poly(oxytetramethylene)diol, poly(ethylene glycol), poly(propylene glycol), and α,ω-dihydroxy terminated polydimethylsiloxane extended with 1,4-butanediol in two-step solution polymerization were obtained. The PU-PDMS were modified using 1.25 mol% of polydimethylsiloxane which was incorporated into main polyurethane backbone as a side chain. The structure of the synthesized PU-PDMS was confirmed by FTIR as well as 1H and 13C-NMR spectroscopy. The effect of different soft segments on free surface energy (FSE) components and thermal stability of poly(urethane-siloxane) copolymers was investigated. The activation energy of the thermal degradation of PU-PDMS using isoconversional methods (Ozawa–Flynn–Wall and Friedman) was calculated. It was concluded that molecular mass, thermal stability, and FSE of PU-PDMS copolymers depend on polyol used. The apparent activation energy at first step of degradation in nitrogen generally increases with the extent of conversion which may result from complex mechanism related to formation of decomposition products. Hydrophobic character of side-chain siloxane on surface properties of the PU-PDMS coatings was confirmed. The obtained coatings are generally soft with the relative hardness in the range of 0.120–0.027. 相似文献
832.
Albrecht Ł Ransborg LK Albrecht A Lykke L Jørgensen KA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(47):13240-13246
This study demonstrates the first enantioselective synthesis of hydroxyalkyl- and aminoalkyl-substituted imidazoles, oxazoles, and thiazoles. The approach developed utilizes a highly effective one-pot reaction cascade that consists of either an organocatalytic epoxidation or aziridination of α,β-unsaturated aldehydes coupled with a [3+2]-annulation, in which amidines, ureas, or thioureas act as effective 1,3-dinucleophilic species. The methodology described benefits from low catalyst loadings, commercially and readily available starting materials, and mild reaction conditions. 相似文献
833.
Bogucka-Kocka A Szewczyk K Janyszek M Janyszek S Cieśla Ł 《Journal of AOAC International》2011,94(1):9-16
Eighteen species belonging to the Carex genus were checked for the presence and the amount of eight phenolic acids (p-hydroxybenzoic, vanillic, caffeic, syringic, protocatechuic, p-coumaric, sinapic, and ferulic) by means of HPLC. Both the free and bonded phenolic acids were analyzed. The majority of the analyzed acids occurred in the studied species in relatively high amounts. The highest concentrations found were caffeic acid and p-coumaric acid, for which the detected levels were negatively correlated. A very interesting feature was the occurrence of sinapic acid, a compound very rarely detected in plant tissues. Its distribution across the analyzed set of species can be hypothetically connected with the humidity of plants' habitats. Several attempted tests of aggregative cluster analysis showed no similarity to the real taxonomical structure of the genus Carex. Thus, the phenolic acids' composition cannot be considered as the major taxonomical feature for the genus Carex. 相似文献
834.
R. Piramidowicz K. Ławniczuk M. Nakielska J. Sarnecki M. Malinowski 《Journal of luminescence》2008,128(5-6):708-711
In this work we present and discuss the dependence of ultraviolet (UV) photoluminescence of praseodymium ion (Pr3+):YAG crystalline waveguides, produced by liquid phase epitaxy, on activator concentration. Praseodymium level influence on UV fluorescence intensity, transition linewidth and dynamics was carefully investigated in order to better understand the nature of processes shaping both the interconfigurational d–f emission and intraconfigurational f–f emissions starting from the 3P0 excited state. The pathways and the role of interconfiguration cross-relaxation in quenching of the UV 4f5d emission are analyzed. 相似文献
835.
Szeleszczuk Łukasz Gubica Tomasz Szmeja Sebastian Ciesielski Arkadiusz Cyrański Michał K. Pisklak Dariusz M. 《Structural chemistry》2021,32(1):297-307
Structural Chemistry - A reliable method for molecular structure determination, excluding single-crystal X-ray diffraction (SCXRD), has been applied to six methyl glycoside tetrabenzoates. The... 相似文献
836.
Spectral and electrical investigations of the semiconducting (BEDT-TTF)2W6O19 and the metal-like (BEDT-TTF)6(Mo8O26)(DMF)3 salts were performed. The vibrational and electronic spectra of the crystalline samples were analysed and assignment of the vibrational features was proposed. The temperature evolution of the vibrational spectra of the (BEDT-TTF)2W6O19 salt was discussed. 相似文献
837.
Dr. Karolina Hurej Weronika Oszczęda Ewelina Opas Dr. Szymon J. Zelewski Prof. Miłosz Pawlicki Dr. Michał J. Białek Dr. Łukasz Orzeł Prof. Lechosław Latos-Grażyński 《Angewandte Chemie (International ed. in English)》2023,62(28):e202303394
The insertion of palladium(II) into di-p-pyrirubyrin results in mutually convertible bimetallic complexes. Post-synthetic functionalization of one of them yielded bispalladium(II) dioxo-di-p-pyrirubyrin and, after demetallation, dioxo-di-p-pyrirubyrin, introducing for the first time the α,β′-pyridin-2-one unit into the macrocyclic frame. Bispalladium(II) di-p-pyrirubyrin 6 , bispalladium(II) dioxo-di-p-pyrirubyrin 9 , and dioxo-di-p-pyrirubyrin 10 absorb and emit light around 1000 nm and are characterized by high photostability. Thus, they are promising candidates for near-infrared photoacoustic dyes, ideally targeting ( 9 ) the wavelength of Yb-based fiber lasers. The incorporation of an α,β′-pyridine moiety into expanded porphyrins opens a highly interesting area of research due to the attractive optical and coordination properties of the resulting molecules. 相似文献
838.
We are concerned with the Cauchy problem for the two-dimensional compressible Navier-Stokes equations supplemented with general H1 initial velocity and bounded initial density not necessarily strictly positive: it may be the characteristic function of any set, for instance. In the perfect gas case, we establish global-in-time existence and uniqueness, provided the volume (bulk) viscosity coefficient is large enough. For more general pressure laws (like e.g., with ), we still get global existence, but uniqueness remains an open question. As a by-product of our results, we give a rigorous justification of the convergence to the inhomogeneous incompressible Navier-Stokes equations when the bulk viscosity tends to infinity. In the three-dimensional case, similar results are proved for short time without restriction on the viscosity, and for large time if the initial velocity field is small enough. 相似文献
839.
840.
Jan Łukaszczyk Piotr Benecki Katarzyna Jaszcz Monika Śmiga 《Macromolecular Symposia》2004,210(1):457-464
Polysuccinates with pendant allyl groups (PSAGE) were synthesized by melt copolymerization of succinic anhydride with allyl glycidyl ether and eventually other glycidyl ethers. It was found that PSAGE could be crosslinked by radical copolymerization with methyl methacrylate. Oxidized PSAGE considered as multifunctional epoxy resin was cured with use of glutaric anhydride to form solid material susceptible to hydrolytic degradation to water-soluble non-toxic products. Comb-like amphiphilic polysuccinates containing both pendant poly(oxyethylene) chains and epoxy groups have been synthesized as well and checked for their solubility in water. Properties of PSAGE-type polymers suggests their potential use as biomaterials and polymeric drug carries. Please note, in the print publication of D. Theis, T. Schmidt, K.-F. Arndt, Macromol. Symp. 210 (2004), 465, erroneously the DOI 10.1002/masy.200450651 is repeated. There, the DOI should read: 10.1002/masy.200450652 相似文献