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991.
992.
Zbigniew Bartczak 《Journal of Polymer Science.Polymer Physics》2010,48(3):276-285
Samples of ultra‐high molecular weight polyethylene, in which the chain topology within the amorphous component was altered using two‐stage processing, including crystallization at high pressure in the first step, were produced and their deformation behavior in the plane‐strain compression was studied. Deformation and recovery experiments demonstrated that the state of the molecular network governed by entanglement density is one of the primary parameters controlling the response of the material on the imposed strain, especially at moderate and high strains. Any change in the concentration of entanglements markedly influences the shape of the true stress–true strain curve. The strain hardening modulus decreases while the onset of strain hardening increases with a decrease of the entanglement density within the amorphous component. Density of entanglements also influences the amount of rubber‐like recoverable deformation and permanent plastic flow. In material of the reduced concentration of entanglements permanent flow appears easier and sets in earlier than in the material with a higher entanglement density, becoming a favorable deformation mechanism at moderate strains. As a result, strong strain hardening is postponed to higher strain when compared with the samples of equilibrium entanglement density. In the samples of an increased entanglement density the molecular network becomes stiffer, with a reduced ability of strain induced disentangling of chains. Consequently, there is a less permanent flow and strain hardening begins earlier than in the reference material of an unaltered chain topology. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 276–285, 2010 相似文献
993.
994.
Zbigniew Kałuża Krzysztof Bielawski Rafał Ćwiek Piotr Niedziejko Przemysław Kaliski 《Tetrahedron: Asymmetry》2013,24(21-22):1435-1442
The synthesis of novel, enantiomerically pure C2-symmetrical hemiaminal ethers and diamines containing piperazine core is presented. The key steps of the synthesis involve the dimerization of an in situ generated α-amino aldehyde into the corresponding cyclic bis-hemiaminal, followed by dehydration in the presence of a base to give a 7-oxa-2,5-diaza-bicyclo[2.2.1]heptane derivative, which can be regarded as a bicyclic bis-hemiaminal inner ether. These compounds represent a new class of molecule, with a structure unambiguously established for the first time. Finally, sodium triacetoxy-borohydride reduction gave the corresponding diamines. Both classes of compounds, new diamines and hemiaminal ethers, were shown to be good ligands for the copper(II)-catalyzed desymmetrization of meso-diols (up to 87% ee) and Henry reactions (up to 84% ee). 相似文献
995.
Ellnain Marek Hubicka Urszula Żuromska Barbara Janeczko Zbigniew Krzek Jan 《平面色谱法杂志一现代薄层色谱法》2011,24(3):248-252
JPC – Journal of Planar Chromatography – Modern TLC - Erigeron canadensis is an annual plant of the Asteraceae family, widely distributed in rural and urban areas of Poland and other... 相似文献
996.
997.
Lilianna Chciska Lesaw Siero Maria Bukowska‐Strzyewska Zbigniew H. Kudzin Lszl Fbin 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(1):o46-o50
The structures of diphenyl [3‐methyl‐1‐(3‐phenylthioureido)butyl]phosphonate and diphenyl [2‐methyl‐1‐(3‐phenylthioureido)butyl]phosphonate, both C24H27N2O3PS, are reported. In both compounds, the thiourea moiety adopts a syn–syn conformation (i.e. the S—C—N—C torsion angles are synperiplanar), which enables N—H⋯O hydrogen bonds to be formed between centrosymmetrically related molecules. The geometries around the P atoms can be described as distorted tetrahedral. Some of the functional groups in each structure are disordered. The bulk of the different alkyl substituents between the amide and phosphonate groups influences the molecular conformation and crystal packing. Although the structures of these compounds and two related derivatives appear to be similar, they are not isostructural. 相似文献
998.
Monika Kijewska Dorota Gszczyk Remigiusz Bchor Piotr Stefanowicz Zbigniew Szewczuk 《Molecules (Basel, Switzerland)》2021,26(22)
Peptide modification by a quaternary ammonium group containing a permanent positive charge is a promising method of increasing the ionization efficiency of the analyzed compounds, making ultra-sensitive detection even at the attomolar level possible. Charge-derivatized peptides may undergo both charge remote (ChR) and charge-directed (ChD) fragmentation. A series of model peptide conjugates derivatized with N,N,N-triethyloammonium (TEA), 1-azoniabicyclo[2.2.2]octane (ABCO), 2,4,6-triphenylopyridinium (TPP) and tris(2,4,6-trimetoxyphenylo)phosphonium (TMPP) groups were analyzed by their fragmentation pathways both in collision-induced dissociation (CID) and electron-capture dissociation (ECD) mode. The effect of the fixed-charge tag type and peptide sequence on the fragmentation pathways was investigated. We found that the aspartic acid effect plays a crucial role in the CID fragmentation of TPP and TEA peptide conjugates whereas it was not resolved for the peptides derivatized with the phosphonium group. ECD spectra are mostly dominated by cn ions. ECD fragmentation of TMPP-modified peptides results in the formation of intense fragments derived from this fixed-charge tag, which may serve as reporter ion. 相似文献
999.
1000.
Magdalena Szumera Barbara agowska Justyna Suowska Piotr Jele Zbigniew Olejniczak Radosaw Lach Anna Berezicka Agnieszka Kijo-Kleczkowska 《Molecules (Basel, Switzerland)》2022,27(3)
Glasses and devitrificates from the SiO2–B2O3–P2O5–K2O–CaO–MgO system with constant contents of SiO2 and P2O5 network formers, modified by the addition of B2O3, were analyzed. All materials were synthesized by the traditional melt-quenching technique. The glass stability (GS) parameters (Krg, ∆T, KW, KH) were determined. The effect of the addition of B2O3 on the GS, liquation phenomenon, crystallization process, and the type of crystallizing phases were examined using SEM-EDS, DSC, XRD, and Raman spectroscopy imaging methods. It was observed that the addition of B2O3 increased the tendency of the glass to crystallize. Both phosphates (e.g., Ca9MgK(PO4)7, Mg3Ca3(PO4)4), and silicates (e.g., K2Mg5(Si12O30), CaMg(Si2O6), MgSiO3) crystallized in the studied system. The Raman spectrum for the orthophosphate Mg3Ca3(PO4)4 stanfieldite type was obtained. Boron ions were introduced into the structures of crystalline compounds at high crystallization temperatures. The type of crystallizing phases was found to be related to the phenomenon of liquation, and the order of their occurrence was dependent on the Gibbs free enthalpy. 相似文献