Influence de la temperature de polymerisation sur le taux de branchement de divers polybenzofurannes obtenus par amorçage cationique

Several polybenzofuranes, obtained by cationic initiation at various temperatures, have been fractionated by preparative G.P.C. The fractions have been studied by various physical methods, mainly osmometry, light scattering, viscometry and G.P.C. These determinations have been made in benzene and the Mark-Houwink relations have been obtained. From the differences observed between these various relations, the gyration radii and the determination of branching indexes, we have found very numerous branches in the samples obtained at the highest temperatures. These branches very probably result from a Friedel-Crafts attack on benzene rings by the carbocations of growing chains. Quantum chemistry determinations are in agreement with this view.     

Ring opening metathesis polymerization catalysts

Over the past eight years, early transition metal catalysts for the ring opening metathesis polymerization of cyclic olefins have been developed. These catalysts are simple organometallic complexes containing metal carbon multiple bonds that in most cases polymerize olefins by a living process. These catalysts have been used to prepare a family of near monodispersed and structurally homogeneous polymers. A series of group VIII ROMP catalysts that allow a wide range of functionality to be incorporated into the polymer side chains have recently been prepared. This most important members of this family of complexes are the bisphosphinedihaloruthenium carbene complexes. These catalysts show excellent functional group stability and can be used to prepare well defined telechelic polymers, polyolefins with ordered functionality, and highly functionalized block copolymers.     

Preparation of new chiral building blocks: highly enantioselective reduction of prochiral 1,3-cycloalkanediones possessing a methyl group and a protected hydroxymethyl group at their C2 position with baker's yeast or CBS catalyst

Highly enantioselective reduction of five-, six-, seven-, and eight-membered prochiral 1,3-cycloalkanediones possessing a methyl group and a protected hydroxymethyl group at their C2 position with baker's yeast or CBS catalyst and a new efficient and general method for preparing the 1,3-cycloalkanediones have been developed. These baker's yeast mediated reductions were found to produce corresponding ketols with high optical purity (>99% ee) and high yield. All of the prepared ketols and their derivatives, chiral building blocks, have been fully characterized, and their absolute configurations have been determined. These compounds would be useful for the convergent synthesis of complex natural products.     

Reactive surfactants in heterophase polymerization for high performance polymers

 A variety of nonionic reactive surfactants have been prepared from block copolymer precursors. These precursors are formed from a commercially available polyoxyethylene glycol monomethylether as the hydrophilic sequence of the surfactant; this product is used as initiator of ring opening anionic polymerization of butylene oxide. Finally the reactive surfactants are obtained after proper functionalization of the precursor. The reactive surfactants are an inisurf with an asymmetric azo compound, a transurf with a thiol group, and a few surfmers with acrylic, methacrylic, styrenic and α-methyl styrenic reactive groups. These compounds have been engaged in styrene emulsion or dispersion polymerization. Several of them have been found to be useful for preparing stable latices. Received: 22 July 1997 Accepted: 11 December 1997     

Solvent extraction of Cu(II) by Schiff bases—II

Aromatic 2-hydroxyaldehydes have been condensed with a number of aliphatic and aromatic amines to form a series of bi-, tri- and tetradentate Schiff bases. These have been used to extract Cu(II) into chloroform, methyl isobutyl ketone and toluene; most have been found to be effective extractants. The characteristics of these extraction systems have been explained in terms of extraction rates and the stability of the reagents to hydrolysis.     

Some novel organometallic Mn<Superscript>III</Superscript> complexes with porphine and 1,6-diaminohexane

A novel series of Mn^III complexes with 5,10,15,20-tetra(p-tolylporphine) and 1,6-diaminohexane has been synthesized. These complexes have been characterized by UV/Vis, IR, ESI-mass spectra, elemental analysis, conductivity and magnetic susceptibility measurements. These Mn^III porphyrins exhibited a blue shift in soret band in comparison to non-metallated porphyrins. The molar conductance values of these complexes show their non-electrolytic nature in ethanol. The tentative structures have also been proposed. All the complexes have good level of water solubility due to which they may have medicinal as well as other valuable biological applications.     

Capillary electrophoresis-based immunoassays: principles and quantitative applications

The use of CE as a tool to conduct immunoassays has been an area of increasing interest over the last decade. This approach combines the efficiency, small sample requirements, and relatively high speed of CE with the selectivity of antibodies as binding agents. This review examines the various assay formats and detection modes that have been reported for these assays, along with some representative applications. Most CE immunoassays in the past have employed homogeneous methods in which the sample and reagents are allowed to react in solution. These homogeneous methods have been conducted as both competitive binding immunoassays and as noncompetitive binding immunoassays. Fluorescent labels are most commonly used for detection in these assays, but enzyme labels have also been utilized for such work. Some additional work has been performed in CE immunoassays with heterogeneous methods in which either antibodies or an analog of the analyte is immobilized to a solid support. These heterogeneous methods can be used for the selective isolation of analytes prior to their separation by CE or to remove a given species from a sample/reagent mixture prior to analysis by CE. These CE immunoassays can be used with a variety of detection modes, such as fluorescence, UV/Vis absorbance, chemiluminescence, electrochemical measurements, MS, and surface plasmon resonance.     

Syntheses and X-ray crystal structures of poly(pyridylsulfanylmethyl)arenes: new multi-armed molecules

The synthesis of a series of seven new poly(pyridylsulfanylmethyl)arenes is reported. These are readily prepared from either 2- or 4-mercaptopyridine and a poly(bromomethyl)arene in the presence of triethylamine. Compounds with three, four, six and eight pyridylsulfanylmethyl arms are reported. These have been fully characterised and, in four cases, the relative orientations of the pyridylsulfanylmethyl arms have been ascertained by X-ray structural analysis.     

Reduction of pendent ester groups in polycarbonates by use of diborane

A series of polycarbonates with pendent ester groups have been synthesized. These ester groups have been converted to hydroxyl functionalities by reduction with diborane in tetrahydrofuran. The number of methylene groups in the pendent chain has a large effect on the reducibility of the ester.     

Crystal and molecular structure of the hydrochloride of the diterpene alkaloid hetisine

The molecular and crystal structure of hetisine hydrochloride has been obtained and compared with those of the hydrobromide and perchlorate salts. These structures have been investigated as coordinatoclathrates and it has been shown that on changing from chloride to bromide and then to perchlorate a morphotropic transition is observed.Supplementary Data relevant to this article have been deposited with the British Library as Supplementary Publication No. SUB 82140 (9 pages).     

Synthesis and complexation properties of poly(ethylene glycol)-linked mono- and bis-dioxocyclams

Both tri- and tetra(ethylene glycol) linked bis-chromium carbene complexes have been synthesized. These carbene complexes were photolyzed with N-protected imidazolines to give protected azapenams. These were transformed into polyether-linked basket dioxocyclams 4a,b and bis-dioxocyclams 5a,b. These compounds have cavities for the complexation of both "hard" and "soft" metal ions. The complexes of Ni, Ba, and Gd were synthesized.     

Study of spatial correlations in a supercooled molecular system

Spatial heterogeneities have been investigated in a supercooled system composed of diatomic molecules with an associated dipole moment by using the molecular dynamics simulation technique. Pair distribution functions of molecules with different mobilities have been evaluated, and it has been found that molecules belonging to the same dynamic domain are spatially correlated. Molecules with extremely large mobilities form larger clusters than those resulting from random statistics. These clusters are stringlike shaped. The mean cluster size displays a maximum at times between the ballistic and the diffusive regime, approximately at the end of the beta-relaxation zone. The value of this maximum increases upon cooling the system. An analogous profile has been observed for the characteristic cluster length when plotted against time. Agreement with Adam-Gibbs predictions has been encountered when considering these clusters as the basic dynamic units of the theory. For the extremely slow molecules, a cluster distribution has also been encountered. These clusters are smaller than the ones composed by fast molecules; they do not have a quasilinear geometry and no maximum is observed for their mean cluster size.     

Synthesis and characterization of polymethylphenylsilane–polystyrene block copolymers

Block copolymers of polymethylphenylsilane (PMPS) and polystyrene (PS) have been successfully prepared by the condensation of α,ω-dichloro-polymethylphenylsilane with polystyryl-lithium. These new materials have been characterized by UV spectroscopy, ²⁹Si-NMR, and size exclusion chromatography. These block copolymers show a good emulsifying activity to compatibilize blends of the two homopolymers (PMPS and PS). © 1993 John Wiley & Sons, Inc.     

Gravimetric Determination of Mercury(II) and Vanadium(IV) with Benzoylacetanilide

Abstract

Gravimetric methods for the determinations of mercury(II) and vanadium(IV) with benzoylacetanilide have been described. These metals have been separated from commonly associated ions and a procedure for the determination of vanadium content of steel has been developed. By these methods, 14 to 50 mg. of mercury and 5 to 20 mg. of vanadium have been estimated with relative standard deviations of 0.18% and 0.10%, respectively.     

Matrix isolation study of the reactions of CrO2Cl2 with a series of silanes

The reactions between CrO2Cl2 and a series of silanes have been investigated using matrix isolation infrared spectroscopy. Twin-jet codeposition of the two reagents into argon matrices at 14 K followed by irradiation with light of lambda > 300 nm led to the growth of a number of new bands. These have been assigned to the appropriate silanol species formed by oxygen insertion into the Si-H bond, strongly complexed to CrCl2O. The structures and vibrational frequencies of these complexes have been characterized by high-level theoretical calculations. These calculations also support the relative preference for the insertion reaction compared to other possible pathways. Merged-jet codeposition of SiH2Cl2 with CrO2Cl2 at 200 degrees C also led to the formation of the free silanol, HSiCl2OH.     

Ginkgolides: selective acetylations,translactonization, and biological evaluation

Protocols for selective acetylation of the hydroxyl groups of ginkgolide C have been developed. These acetylations have given rise to various ginkgolide C acetates and iso-ginkgolide C acetates, the latter having a rearranged skeleton resulting from translactonization. These acetyl derivatives, as well as ginkgolides A and B acetates have been investigated for their ability to bind to a cloned platelet-activating factor (PAF) receptor.     

双自由基间苯体系铁磁分子设计

采用量子化学从头算UHF方法对不同组成的双自由基及其异构体进行了系统比较,进而对系列双自由基体系的基态自旋耦合规律进行了研究,并讨论了具有空间位阻的顺反异构现象对双自由基自旋耦合的影响。对以双自由基为基础的有机铁磁体的合成具有指导意义。     

Polymerisation de monomeres a structures biologiques

Fixation of biological compounds (cholesterol and testosterone) on (2-hydroxyethyl)methacrylate has been realized by a carbonate linkage. These new monomers have been characterized by N.M.R. and i.r.; they have been polymerized by a radical process. Resulting homopolymers have been analysed and compared with polymers bearing similar active compounds, previously synthesized by chemical modification of poly (2-hydroxyethyl)methacrylate.     

Direct solid sample analysis of SiC-powders by DC glow discharge and DC-ARC emission spectroscopy

Glow discharge atomic emission spectroscopy (GD-OES) and the classical spectrographic method with a dc arc source (DC-ARC OES) have been applied to the direct analysis of SiC powders. The homogeneity of pellets prepared from mixtures of SiC with copper powder and used for the GD experiments was investigated in detail. Various methods have been tested for the analytical calibration. These have been applied to the direct solid sample analysis of technical SiC powders. The experimental data were evaluated by chemometrical procedures. The results of the two methods have been compared.