Propriétés des copolymères biséquencés polyoxyéthylène-polystyrène

Résumé On a préparé des monocristaux de copolymères biséquencés polyoxyéthylène-polystyrène (POE-PS) à partir de leurs solutions diluées, qui peuvent contenir jusqu'à 55% de PS. Les principales formes de ces cristaux et leurs variantes morphologiques, observées sous microscope optique, sont décrites et rattachées à la maille cristallographique du POE. On présente aussi quelques exemples de monocristaux obtenus par ensemencement, dans lesquels les différentes formes se succèdent par filiation; on discute les transitions des formes et leur dépendance vis à vis des conditions de cristallisation.La cristallisation de ces copolymères provoque généralement un fractionnement en composition, car la proportion de PS dans les cristaux est limitée. On propose deux modèles de structure différents, dans lesquels une ou deux couches cristallines de POE en configuration repliée sont recouvertes par le PS amorphe. Le processus de fractionnement est interprété à partir de ces deux structures en admettant une extension critique pour les séquences de PS, dont l'une des extrémités est ancrée sur la surface des repliements du POE.

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Summary Single crystals of copolymers, composed of one Poly(ethylene-oxide), (POE), and one Polystyrene (PS) block, (which may contain 55% of PS, by weight), have been prepared from dilute solutions. The principal crystal habits and their morphological variations, as observed with an optical microscope, are described and related to the unit cell of POE. Single crystals grown from various types of seeds, in which different external habits succeed one another, are also shown. Transitions of crystal habits and their dependence on crystallisation conditions are discussed in some detail.Generally, crystallisation of these copolymers produces some fractionation with respect to composition, for only a limited fraction of the initial PS can enter into the crystal. Two different crystal structures are proposed in which a single, or a double crystalline layer of folded POE is covered by amorphous PS. The fractionation process is interpreted on the basis of these two structural models, assuming a critical extension of the PS blocks anchored at one end to the fold surface of PEO.

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Zusammenfassung Einkristalle von Copolymeren aus einem Polyäthylenoxyd (PEO) und Polystyrol (PS)-Block, die gewichtsmäßig 55% PS enthalten können, wurden aus verdünnten Lösungen präpariert. Der grundsätzliche Charakter der Kristalle und ihre morphologischen Variationen, wie es in einem optischen Mikroskop beobachtet wird, ist beschrieben und mit der Elementarzelle PEO in Beziehung gebracht. Einkristalle, entstanden aus verschiedenen Typen von Kristallkeimen, in welchen verschiedene äußere Formen auftreten, die aufeinanderfolgen, werden gezeigt. Die übrigen Kristallformen und ihre Abhängigkeit von den Kristallisationsbedingungen werden im einzelnen diskutiert.Im allgemeinen verursacht die Kristallisation dieser Copolymeren gewisse Fraktionierung hinsichtlich der Zusammensetzung, da nur eine begrenzte Menge des ursprünglichen Polystyrols in den Kristall eintreten kann. Zwei verschiedene Kristall-Strukturen werden vorgeschlagen, in denen bzw. eine oder zwei Schichten von gefaltetem PEO mit amorphem Polystyrol bedeckt ist. Der Fraktionierungsprozeß wird auf Grund dieser zwei Struktur-Modelle interpretiert, die eine kritische Größe der PS-Blöcke, verankert an einem Ende der gefalteten Oberfläche von PEO, annehmen.

     

Beiträge zur Chemie der Pyrrolpigmente, 9. Mitt.: Bildung,Struktur und Konfiguration vonZ- undE-Arylmethyliden-3,4-dimethyl-3-pyrrolin-2-onen

The condensation of 3.4-dimethyl-3-pyrrolin-2-one with p-methyl-, p-chloro-benzaldehyde and ferrocenealdehyde yields theZ-andE-isomers of the corresponding condensates. Due to kinetic control theZ-isomers are obtained almost exclusively in this reaction. TheE-isomers of the two firstmentioned products can be produced by photochemical isomerization. The structures (tautomeric forms) and configurations of the isomers were established by the Lanthanide-induced-shift-technique and by evaluating the Nuclear-Overhauser-Effect.     

Phase Transition and Crystal Structure of the Monomeric Europium(II) Thiolate Eu(SC36H49)2

Single crystal X‐ray diffraction of Eu(SC₃₆H₄₉)₂ has revealed a first order phase transition at a temperature of 119 K, that involves a reduction of the specific volume by 1 %. The transition corresponds to a doubling of the unit cell, as it is the result from reorientations of isopropyl groups that appear at peripheral sites of the organic ligands. It is argued that a denser packing is achieved at the expense of a less favourable conformation of one of the two crystallographically‐independent complexes in the low‐temperature phase. The Bond‐Valence method is used to show that interactions of equal strengths are present between europium and both sulphur atoms and both coordinating phenyl rings.     

三元配合物钯（Ⅱ）-2,2''-联吡啶-L-天冬氨酸与DNA作用研究

The ternary complex Pd(Ⅱ)-2,2‘-bipyridine-L-asparagic acid was synthesized and characterized by elemental analysis, IR-spectra and molar conductance. The formula of the complex is Pd(bipy)(L-asp). The interaction of the complex with DNA has been studied by UV-spectra, fluorescence spectra, CD-spectra and gel electrophoresis. The results showed that the interaction of the complex with DNA performed mainly in intercalative mode and the extent of interaction was dependent on the concentration of the complex.     

Synthesis and Characterization of Novel Organosoluble Methyl Substituted Poly(aryl Ether Ketone)s Containing Sulfone Linkage

Several new methyl substituted poly(aryl ether ketone)s containing sulfone linkage with inherent viscosities of 0.62–0.84 dL/g have been prepared from 4,4′‐bis(2‐methylphenoxy)diphenylsulfone and 4,4′‐bis(3‐methylphenoxy)diphenylsulfone with terephthaloyl chloride and isophthaloyl chloride by electrophilic Friedel‐Crafts acylation in the presence of DMF with anhydrous AlCl₃ as a catalyst in 1,2‐dichloroethane, respectively. These polymers having weight‐average molecular weight in the range of 71,000–49,000 are all amorphous and show high glass transition temperatures ranging from 167 °C to 191 °C, excellent thermal stability at temperatures over 400 °C in air or nitrogen, high char yields of 51–58% in nitrogen and good solubility in CHCl₃ and polar solvents such as DMF, DMSO and NMP at room temperature.     

Polymer bound glutamic acid salicylaldehyde Schiff‐base complex ­catalyst for oxidation of olefins with ­dioxygen

The polymer bound Schiff‐base ligand (PS‐SalGlu) has been prepared from polystyrene bound salicylaldehyde and glutamic acid, and its complex (PS‐SalGlu‐Co) has also been synthesized. The polymer ligand and its complex were characterized by infrared spectroscopy, small area X‐ray photoelectron spectroscopy, and inductively coupled plasma‐atomic emission spectro (ICP‐AFS). In the presence of the complex, cyclohexene can be effectively oxidized by molecular oxygen without reductant. The long‐chain linear aliphatic olefins, such as 1‐octene, 1‐decene, 1‐dodecene and 1‐tetradecene, can be directly oxidized by molecular oxygen catalyzed by PS‐SalGlu‐Co, which affords the 1,2‐epoxy alkane. Copyright © 2001 John Wiley & Sons, Ltd.     

Thin‐Film Infrared Spectroscopy of Acetonitrile

Acetonitrile and [D₃]acetonitrile in the vicinal region of a planar AgX fiber contain linear dipole–dipole linked oligomers as shown by 1) comparison of infrared band intensity ratios in the gaseous and condensed phases and 2) remarkable plots of absorbance (C? N stretch) versus time during evaporation from an AgX planar fiber element. The plots (CH₃CN 2252 cm^?1, CD₃CN 2262 cm^?1) reveal the presence of octamers, hexamers, tetramers, and dimers along with some heptamer, trimer, and monomer structures. A novel isotope effect arises from the somewhat smaller size of the CD₃CN resulting in an increase in the CN band intensity. The organized oligomers may be termed pseudocrystals and are the main components responsible for absorption intensity in the infrared spectrum of acetonitrile, on the AgX planar fiber or in an IR cell.     

Synthesis of novel poly(ethylene glycol) supported benzazepines: the crucial role of PEG on the selectivity of an intramolecular Heck reaction

Poly(ethylene glycol) (PEG 3400) was used as a soluble polymeric support for the synthesis of a series of novel benzazepines. The key step for the preparation of these heterocycles was a phosphine-free palladium-catalyzed Heck reaction. Palladium nanoparticles formed during the course of the reaction were characterized. The presence of PEG 3400 influenced the outcome of the reaction in terms of selectivity.     

Surface plasmon near-field imaging of very thin microstructured polymer layers

We report on the near-field imaging of microstructured polymer layers deposited on an homogeneous metal thin film on which a surface plasmon mode is excited. The microstructures in the polymer layers are designed by electron beam lithography, and the near-field imaging is performed with a photon scanning tunneling microscope (PSTM). We show that, despite their very small height, the microstructures can be conveniently imaged with a PSTM thanks to the field enhancement at the surface of the metal thin film supporting the surface plasmon. The influence of the illumination conditions on the contrast of the PSTM images is discussed. In particular, we show that both the field enhancement and the near-field intensity distribution around the microstructures depend dramatically upon the illumination conditions, leading to the conclusion that the PSTM is well suited for spatially resolved near-field surface plasmon sensing purposes.