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991.
Isabelle Dchamps-Olivier Jean-Pierre Barbier Michel Aplincourt Nicolas Oget Franoise Chuburu Henri Handel 《Helvetica chimica acta》1999,82(5):790-795
The acid-base behavior of cyclenphosphine sulfide (cyclenPS) is appreciably different from that of cyclamphosphine sulfide (cyclamPS). The cyclenPS shows five acid functionalities compared to four for cyclamPS. The fifth acidic group in cyclenPS corresponds to the formation of a stable amidure in aqueous solution (pK=12.3). This behavior is due to the strong transannular N→P interaction. The deprotonation sequences were established by 31P-NMR and confirmed by modelling of cyclenPS. 相似文献
992.
Henri Cramail Alain Deffieux Jean-Noêl Pédeutour Karunakaran Radhakrishnan 《Macromolecular Symposia》2002,183(1):113-120
In this paper, we investigate different routes to lower drastically the amount of methylaluminoxane (MAO) required to activate racEt(Ind)2ZrX2 catalysts towards olefin polymerization. A first approach consists in replacing Cl ligands by more easily extractable X groups such as Me, CH2Ph or NMe2 groups. A second method focuses on the preparation of TMA-depleted MAO either by pumping off TMA from commercial MAO or by exploring new synthetic source to MAO via non-hydrolytic processes such as the reaction of TMA with benzophenone. Both methods allowed us to produce polyolefins with a maximal catalytic activity for Al/Zr ratios not exceeding 150, i.e. ratio 20 times lower than those required in the presence of commercial MAO. 相似文献
993.
994.
In order to determine the influence of the dielectric field intensity on the crosslinking reaction under microwaves, pulsed waves were used to cure epoxy-amines systems, without catalyst. Cured resins were studied by Fourier transform infrared spectroscopy, 13-C nuclear magnetic resonance and dynamic mechanical thermal analysis. Structural and mechanical properties were found to be influenced by parameters as pulse repetition period and peak pulse power. 相似文献
995.
996.
Among the polymer families, aliphatic polyesters stand out from this category thanks to their degradable and biocompatible properties. In particular, the γ-lactones differ from other lactones by yielding polyesters that can be depolymerized back to the monomer and offer the advantage of counting various biobased monomers. As an example, α-hydroxy-γ-butyrolactone (HBL) is a hydroxy-functionalized monomer that can be obtained by a biological synthetic route from glucose. In this article, the ring-opening copolymerization (ROCP) of HBL and l -lactide (LLA) using t-BuP4 as catalyst is investigated. The copolymerizations were conducted within a temperature range of 5–100°C, affording monomer conversions exceeding 80%. The characterization of the copolyesters revealed a branched structure consisting of different HBL patterns, including cyclic, linear, and branched motives. Performing a kinetic study of the copolymerization at room temperature provided a deeper understanding of the mechanism. By modulating the reaction parameters, copolymers of low molar masses with an HBL content of up to 33% were synthesized. High molar mass LLA/HBL-based copolyesters, with up to 290,000 g/mol, were synthesized by a straightforward chain coupling reaction with a diisocyanate. 相似文献
997.
Hélène Lavanant Henri Virelizier Yannik Hoppilliard 《Journal of the American Society for Mass Spectrometry》1998,9(11):1217-1221
The relative proportion of 1:1 Cu(I)– and Cu(II)–peptide complexes PeptCu(I)+ and [Pept?H+Cu(II)]+ yielded by electrospray ionization of copper sulfate and GlyHisLys solutions in water/methanol was examined under different source conditions. Two factors leading to an increase in Cu(I) complex ratio were found. (1) Increase of nozzle–skimmer voltages caused collision-induced dissociation of Cu(II) complexes, and most probably favor ligand-to-metal electron transfers that result in the decoordination of oxydated ligands to form PeptCu+. (2) Independent of these “innersphere” processes that involve only electron exchange inside the coordination sphere around the metal cation, an increase in source voltages with a concomitant increase of current and, supposedly, electron counterflow between the counterelectrode and the capillary caused an increase in PeptCu+ relative proportion. The hypothesis that an “outersphere” electron capture might happen in these conditions was verified by using discharge supressing SF6 gas as nebulizing gas. The electronegative gas reduced the current brought on by high voltages and inhibited the PeptCu+ increase phenomenon. 相似文献
998.
Marie‐Pierre Comard Rachel Calvet Sylvie Del‐Confetto John A. Dodds Henri Balard 《Macromolecular Symposia》2001,169(1):19-34
Inverse Gas Chromatography at Infinite Dilution, i.e. IGC‐ID, allows following the evolution of surface properties of talc impregnated with increasing concentrations of polyethyleneglycol of molecular weight 20,000. Coupling Inverse chromatography in infinite dilution conditions measurements with controlled surface modification, we have developed a new method to estimate the lateral to basal surface ratio of talc crystals. 相似文献
999.
1000.