NMR techniques in emulsion polymer investigation

This paper is a brief survey showing the versatility and unicity of NMR spectroscopy for characterizing the macromolecular architecture in copolymers originated from an emulsion process. Three cases are more particularly described using various NMR techniques i) to carry out high resolution ¹³ C NMR in order to investigate the microstructure (mainly the monomer sequence distribution as a function of process variables, ii) to perform direct analysis of latex particles by ¹³ C NMR so as to get insight on the surface morphology of functional particles, iii) to deal with solid-state NMR on as-dried particles (or films) in order to obtain quantitative information on the internal morphology of composite latexes.     

Modelling and simulation of synthesis,microstructure and properties of emulsion copolymers

Accurate investigations of batch homopolymerization and copolymerization allow to derive mechanisms for emulsion polymerization; if they are not actually general, they are assumed to be valid for a given co-monomer system, at least. A lot of approaches have been devoted to the mathematical modelling of emulsion polymerization, with the objective to take into account all of the experimental parameters or only some of them. Many of these approaches are quite complex and assume that a huge number of parameters are known.     

Quantum theory of the magneto-optical effect induced by Ni ions in barium ferrites

To reveal the physical origin of the giant magneto-optical enhancement of Ni²⁺ ions in barium ferrite, quantitative calculations of the contributions of both the intra-ionic electric dipole transition between the 3d⁸ and 3d^{7 4p} configurations of the Ni²⁺ ions and the intra-ionic electric dipole transition induced by odd-parity crystal field terms are presented. It is deduced that the transition is important in the origin of the considered magneto-optical enhancement. The most important factor is the Ni-Fe superexchange interaction; since it is strong enough, the Faraday rotation produced by the Ni²⁺ ions is large though the energy difference between the 3d⁸ and 3 d7 4 p configurations is large. It is demonstrated that though the intra-ionic electric dipole transition does produce Faraday rotation peaks in the visible range, their magnitude is too small to explain the observed Faraday rotation. The effect of the spin-orbit interaction on the Faraday rotation is analysed. The spin-orbit interaction of the ground configuration plays a very important role in the occurrence of Faraday effects, but the Faraday rotation does not increase linearly with the strength of the spin-orbit coupling. On the contrary, the spin-orbit interaction of the excited configuration has almost no effect on the Faraday rotation. It is shown that the mixing of the different multiplets of the ground term induced by the crystal field has a great influence on the magneto-optical properties. Received 7 January 1998     

A Tale of Two Complexes: Electro-Assisted Oxidation of Thioanisole by an “O2 Activator/Oxidizing Species” Tandem System of Non-Heme Iron Complexes

We report two new Fe^III complexes [L¹Fe^III(H₂O)](OTf)₂ and [L²Fe^III(OTf)] , obtained by replacing pyridines by phenolates in a known non-heme aminopyridine iron complex. While the original, starting aminopyridine [(L₅ ² )Fe^II(MeCN)](PF₆) complex is stable in air, the potentials of the new Fe^III/II couples decrease to the point that [L²Fe^II] spontaneously reduces O₂ to superoxide. We used it as an O₂ activator in an electrochemical setup, as its presence allows to generate superoxide at a much more accessible potential (>500 mV gain). Our aim was to achieve substrate oxidation via the reductive activation of O₂. While L²Fe^III(OTf) proved to be a good O₂ activator but a poor oxidation system, its association with another complex (TPEN)Fe^II(PF₆)₂ generates a complementary tandem couple for electro-assisted oxidation of substrates, working at a very accessible potential: upon reduction, L²Fe^III(OTf) activates O₂ to superoxide and transfers it to (TPEN)Fe^II(PF₆)₂ leading in fine to the oxidation of thioanisole.     

A technique for cyclic-plastic notch-strain measurement

The interferometric strain/displacement gage was used to measure local strains of approximately ± 1 percent strain near a central notch in specimens undergoing completely reversed loading. Two notch geometries were tested: a circular hole and a keyhole slot with theoretical stress-concentration factors of 3.1 and 5.9 respectively. Measurements were made at both room and elevated temperatures (149° and 260°C) on three materials having different cyclic properties. This paper describes the experimental techniques for making the notch-strain measurements. The results of this series of tests are used in evaluating Neuber's cyclic rule.     

Cayley graphs and automatic sequences

We study those automatic sequences which are produced by an automaton whose underlying graph is the Cayley graph of a finite group. For 2-automatic sequences, we find a characterization in terms of what we call homogeneity, and among homogeneous sequences, we single out those enjoying what we call self-similarity. It turns out that 2-self-similar sequences (viewed up to a permutation of their alphabet) are in bijection with many interesting objects, for example dessins d’enfants (covers of the Riemann sphere with three points removed). For any p, we show that, in the case of an automatic sequence produced “by a Cayley graph,” the group and indeed the automaton can be recovered canonically from the sequence. Further, we show that a rational fraction may be associated with any automatic sequence. To compute this fraction explicitly, knowledge of a certain graph is required. We prove that for the sequences studied in the first part, the graph is simply the Cayley graph that we start from, and so calculations are possible. We give applications to the study of the frequencies of letters.     

Regioselective Hydroarylation Reactions of C3 Electrophilic N‐Acetylindoles Activated by FeCl3: An Entry to 3‐(Hetero)arylindolines

A method for the direct and rare umpolung of the 3 position of indoles is reported. The activation of N‐acetylindole with iron(III) chloride allows the C?H addition of aromatic and heteroaromatic substrates to the C2?C3 double bond of the indole nucleus to generate a quaternary center at C3 and leads regioselectively to 3‐arylindolines. Optimization, scope (50 examples), practicability (gram scale, air atmosphere, room temperature), and mechanistic insights of this process are presented. Synthetic transformations of the indoline products into drug‐like compounds are also described.     

Seife, Waschmittel

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Einen Beitrag zum Studium der Pasten

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