Supramolecular polymer hydrogels induced by host-guest interactions with di-[cyclobis(paraquat-p-phenylene)] cross-linkers: from molecular complexation to viscoelastic properties

Supramolecular polymer networks have been designed on the basis of a -electron donor/acceptor complex: naphthalene (N)/cyclobis(paraquat-p-phenylene) (CBPQT4+=B). For this purpose, a copolymer of N,N-dimethylacrylamide P(DMA-N1), lightly decorated with 1 mol% of naphthalene pendant groups, has been studied in semi-dilute un-entangled solution in the presence of di-CBPQT4+ (BB) crosslinker type molecules. While calorimetric experiments demonstrate the quantitative binding between N and B groups up to 60 °C, the introduction of BB crosslinkers into the polymer solution gives rise to gel formation above the overlap concentration. From a comprehensive investigation of viscoelastic properties, performed at different concentrations, host/guest stoichiometric ratios and temperatures, the supramolecular hydrogels are shown to follow a Maxwellian behavior with a strong correlation of the plateau modulus and the relaxation time with the effective amount of interchain cross-linkers and their dissociation dynamics, respectively. The calculation of the dissociation rate constant of the supramolecular complex, by extrapolation of the relaxation time of the network back to the beginning of the gel regime, is discussed in the framework of theoretical and experimental works on associating polymers

An easy and economically viable route for the decoration of carbon nanotubes by magnetite nanoparticles, and their orientation in a magnetic field

peer reviewedA simple, cheap and tunable approach for the decoration of carbon nanotubes by magnetite nanoparticles and their orientation in a magnetic field is reported.Eurocores program, SON

Al(OPri)3-catalysed halogen exchange processes of relevance to atom transfer radical polymerization: the effect depends on the metal electronic structure

International audienceWhether or not tri(isopropoxo)aluminium catalyses halogen exchange for an ATRP catalyst depends on the number of valence electrons

Etudes de processus de polymérisation radicalaire contrôlée par des complexes de molybdène

Des complexes organométalliques et de coordination à base de molybdène (Mo) ont été étudiés en polymérisation radicalaire contrôlée. Ce travail a permis de montrer qu'une nouvelle famille de complexes du type CpMoX2L2 (avec L2 = R2-diazadiène et X = Cl, I) est active en polymérisation radicalaire contrôlée du styrène et des acrylates. Une étude sur le mode d'action d'un cocatalyseur (Al(OiPr)3) est présentée. Une nouvelle voie de synthèse des précurseurs des complexes de coordination de Mo(IV) et de Mo(III) a été développée. L'utilisation de complexes simples de coordination en polymérisation radicalaire contrôlée du styrène est décrite. Une étude mécanistique a montré que le processus de propagation du radical actif sous des conditions d'ATRP doit être similaire à celui d'une polymérisation radicalaire classique. Une étude sur des complexes de Mo(II) a permis, entre autres, de montrer qu'un catalyseur cationique de CpMo(II) peut également contrôlée la polymérisation de l'acrylate de méthyle.Organometallic and coordination complexes of molybdenum (Mo) have been studied in controlled radical polymerisation. A new tunable family of CpMoX2L2 complexes (L2 = R2-diazadiene; X = Cl, I) active in ATRP has been introduced. The ATRP method with organometallic Mo complexes has been extended successfully to acrylate monomers and to a PMA-b-PS block copolymer. A reasonable hypothesis for the role of Al(OiPr)3 on the ATRP rate has been formulated. A relationship between electronic structure and Al(OiPr)3 catalysis for the halogen exchange between ATRP catalyst and initiator has been dicovered. New and simpler syntheses of the commonly used MoCl4(Et2O)2 and MoCl3(THF)3 starting materials have been optimized. Simple (non organometallic) coordination compouds of Mo(III) are effective for the ATRP of styrene. New organometallic compounds of Mo(II) containing a diazadiene ligand have been synthesized; complex CpMo(CO)2(iPr2-dad)+,I- is capable of controlling the radical polymerisation of methyl acrylate.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Half-sandwich molybdenum(III) compounds containing diazadiene ligands and their use in the controlled radical polymerization of styrene

International audienceThe reaction of CpMoCl2 with diazadiene ligands RN=CH-CH=NR (R2-dad) affords the corresponding paramagnetic complexes CpMoCl2(R2-dad) (R = Ph, 1; p-Tol, 2; C6H3Pri2-2,6, 3; and Pri, 4). All compounds have been characterized by EPR spectroscopy and have been investigated by cyclic voltammetry. They display one-electron oxidation and reduction processes, these being reversible or irreversible depending on the nature of R. The irreversibility of the reduction wave is due to a chemical follow-up process which consists of chloride loss from the reduced product. This phenomenon is suppressed ion the presence of excess chloride in solution. An X-ray structure of 3 verifies the mononuclear natureof the compound and the chelating mode of the dad ligand, the MoN2C2 ring being essentially planar. The N-C and C-C bond distance pattern suggests the important contribution of an enediamido Mo(V) limiting form. In the presence of 1-bromoethylbenzene, complexes 1-4 catalyze the controlled/”living” radical polymerization of styrene. Complex 3 also leads to a controlled/”living” radical polymerization of styrene in the presence of AIBN as a radical generator. Therefore, this is the second example of a compound which is capable of controlling the styrene radical polymerization under both ATRP and SFRP conditions

Polymérisation radicalaire par transfert d’atome du styrène contrôlée par des composés de coordination de Mo(III)/Mo(IV) contenant des ligands phosphines

International audienceA controlled polymerisation of styrene has been achieved under ATRP conditions by using a phosphine-containing MoIII/MoIV system. Linearity of the Mn vs conversion plot and low PDI’s are observed in bulk, in a 30% (v/v) PhCl solution, and in a chain extension experiment when using MoCl3(PMe3)3/BIB. Controlled polymerisation is also observed for a reverse ATRP experiment starting from MoCl4(PMe3)3/AIBN. The absence of chain transfer and termination is confirmed by NMR and MALDI–TOF analyses of polymers obtained by employing BEB and BIB as initiators.Cet article décrit la possibilité d'effectuer une polymérisation contrôlée du styrène en utilisant un système de complexes de coordination de MoIII/MoIV contenant des ligands phosphines. La propagation procède selon un mécanisme de transfert d'atome par voie radicalaire (ATRP) en utilisant le complexe MoCl3(PMe3)3 et l’amorceur PhCH(Br)CH3 (BEB). En effet, celui-ci a été prouvé par une série d'expériences : polymérisation en masse et en solution, essais d’extension de chaîne et de catalyse inverse (par utilisation du complexe MoCl4(PMe3)3 et une source de radicaux libres, le composé AIBN). Les résultats obtenus montrent une bonne linéarité des masses moléculaires en fonction du taux de conversion du monomère et les indices de polydispersités sont relativement faibles. Des analyses du polymère par RMN et MALDI-TOF-MS ont permis d'exclure la présence de transfert de chaîne et de terminaisons bimoléculaires au cours du processus

Improved Preparations of Molybdenum Coordination Compounds from Tetrachlorobis(diethyl ether)molybdenum(IV)

International audienceThe reduction of MoCl5 with metallic tin in diethyl ether provides a rapid and convenient entry to [MoCl4(OEt2)2] This compound can be transformed easily and in high yields into a variety of other useful synthons. The loss of ether in the solid state affords a new and reactive form of MoCl4. Treatment with THF, PMe3 or LiOtBu affords [MoCl4(THF)2], [MoCl4(PMe3)3] or [Mo(OtBu)4] in high isolated yields. Treatment with metallic tin in THF affords [MoCl3(THF)3] All of these reactions can be carried out under simple experimental conditions and represent significant improvements relative to previously reported syntheses of the same compounds

A Bis(diazadiene) Adduct of MoCl2: Mononuclear, Octahedral, Undistorted and Diamagnetic

International audienceThe complex [MoCl2(iPr2dad)2] (iPr2dad = iPrN=CH−CH=N−iPr) is obtained in one step by reduction of [MoCl3(THF)3] in the presence of iPr2dad. The X-ray structure reveals a relatively undistorted octahedral coordination geometry with a relative cis configuration and points to a more appropriate description of the ligands as enediamides. The NMR investigation is in agreement with the same cis structure in solution and underlines the diamagnetism of the compound, at odds with previously reported very similar complexes. A bulk magnetic susceptibility measurement further confirms the compound’s diamagnetism. No equilibrium with a dinuclear, metal-metal bonded species is apparent from the solution studies. A DFT calculation on the real molecule and on two R2dad model systems with R = Ph and 4-HOC6H4 reveals how the ligand periphery delicately controls the magnetic and structural properties of this system

Combination of ring-opening polymerization and "click" chemistry towards functionalization of aliphatic polyesters

Azide pendent groups of aliphatic polyesters have been derivatized into tertiary amines, ammonium salts and poly(ethylene oxide) grafts. The experimental conditions have been optimized (organic solvent, 35 degrees C), such that the aliphatic polyesters are not degraded, including even poly(lactide) which is very sensitive to attack by weak nucleophiles