References of "Brédas, Jean-Luc"
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See detailElectrodeposition of mixed adherent thin films of poly(ethyl acrylate) and polyacrylonitrile onto nickel
Baute, Noëlle; Geskin, Victor M; Lazzaroni, Roberto et al

in e-Polymers (2004), (63), 1-20

Adherent thin polymer films have been prepared by sequential electrodeposition of ethyl acrylate (EA) and acrylonitrile (AN) onto nickel. Their composition has been studied by IR spectroscopy and time of ... [more ▼]

Adherent thin polymer films have been prepared by sequential electrodeposition of ethyl acrylate (EA) and acrylonitrile (AN) onto nickel. Their composition has been studied by IR spectroscopy and time of flight-secondary ion mass spectrometry. Morphology and thickness have been analyzed by atomic force microscopy and ellipsometry, respectively, and compared to single component films of PEA and PAN. No microphase separation was detected in the mixed PEA/PAN films. These show a granular morphology comparable to that of PAN films. The grains contain the two constitutive polymers, as confirmed by the selective thermal degradation of PEA. [less ▲]

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See detailFull-electrochemical preparation of conducting/insulating binary polymer films
Jérôme, Christine ULg; Geskin, V.; Lazzaroni, Roberto et al

in Chemistry of Materials (2001), 13(5), 1656-1664

Binary polymer films consisting of an insulating polymer and a conducting polymer have been successfully prepared by sequential electropolymerization of the parent monomers. The insulating polymer ... [more ▼]

Binary polymer films consisting of an insulating polymer and a conducting polymer have been successfully prepared by sequential electropolymerization of the parent monomers. The insulating polymer (polyacrylonitrile or polyethylacrylate) is formed under cathodic polarization in a potential range where the growing chains are chemically grafted onto the nickel or carbon electrode. The conducting polymer (polybithiophene or polypyrrole) is formed by electrooxidation of the parent monomer. The electrochemical reactions and the electrochemical properties of the films have been analyzed by cyclic voltammetry and chronoamperometry. The influence of the main experimental parameters on the composition and morphology of the films has been investigated by X-ray photoelectron spectroscopy and atomic force microscopy. This approach strongly improves the adhesion of the conducting polymer as a result of its combination with the grafted polyacrylonitrile. This combination of insulating and conducting polymers is a way to tune the electroactivity of the conjugated chains. [less ▲]

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See detailElectrochemical strategies for the strengthening of polymer – metal interfaces
Baute, Noëlle; Jérôme, Christine ULg; Martinot, Lucien et al

in European Journal of Inorganic Chemistry (2001), 2001(5), 1097-1107

Polymers have been widely used for the protection of metals against corrosion and for improving the performance of structural adhesive joints. In this contribution, the weakness and short-term durability ... [more ▼]

Polymers have been widely used for the protection of metals against corrosion and for improving the performance of structural adhesive joints. In this contribution, the weakness and short-term durability of these polymer-metal interactions and some common approaches for alleviating this problem are briefly reviewed. Among the existing techniques, electrochemical processes offer the advantage of controlled interfacial reactions. Promising results have been reported by Strat-mann et al. and Le´cayon et al., who have emphasized the interest and opportunity to create strong chemical bonds between the organic coating and the metallic substrate. Their work is discussed in this review, along with results recently obtained in our group [less ▲]

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See detailMorphology and mechanical properties of poly(methylmethacrylate)-b-poly(alkylacrylate)-b-poly(methylmethacrylate)
Tong, J. D.; Leclère, Philippe; Doneux, C. et al

in Polymer (2001), 42(8), 3503-3514

A series of well-defined poly(methylmethacrylate) (PMMA)-b-poly(alkylacrylate)-b-PMMA triblock copolymers (MAM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate)-b-PMMA ... [more ▼]

A series of well-defined poly(methylmethacrylate) (PMMA)-b-poly(alkylacrylate)-b-PMMA triblock copolymers (MAM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate)-b-PMMA precursors by alkyl alcohols. The molecular weight (MW) of the outer PMMA blocks is in the 10,000-50,000 range, compared to 50,000-200,000 for the inner poly(alkylacrylate) block. Phase separation, as studied in direct space by atomic force microscopy, is observed for all the investigated triblock copolymers, except for the PMMA-b-poly(ethylacrylate)-b-PMMA and the PMMA-b-poly(n-propylacrylate)-b-PMMA triblocks of 10,000-50,000-10,000 MW. The ultimate tensile strength measured for the MAM triblocks is strongly dependent on the MW between chain entanglements for the central block. The tensile behavior is however affected by the partial miscibility of the outer and inner blocks when the PMMA MW is low. When this situation prevails, it makes the melt processing possible at temperatures lower than 200°C. [less ▲]

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See detailPhase-separated microstructures in "all-acrylic" thermoplastic elastomers
Leclère, Philippe; Rasmont, A.; Brédas, Jean-Luc et al

in Macromolecular Symposia (2001), 167

Atomic Force Microscopy (AFM) is used to study the phase separation process occurring in block copolymers in the solid state. Measuring simultaneously the amplitude and the phase of the oscillating ... [more ▼]

Atomic Force Microscopy (AFM) is used to study the phase separation process occurring in block copolymers in the solid state. Measuring simultaneously the amplitude and the phase of the oscillating cantilever in tapping-mode operation provides the surface topography along with the cartography of microdomains with different mechanical properties. This in turn allows to characterize the organization of the various components at the surface in terms of well-defined morphologies (e.g., spheres, cylinders, or lamellae). Here this approach is applied to a series of symmetric triblock copolymers made of a central elastomeric segment (polyalkylacrylate) surrounded by two thermoplastic sequences (polymethylmethacrylate). The occurrence of microphase separation in these materials and the resulting microscopic morphology are essential factors for determining their potential applications as a new class of thermoplastic elastomers. This paper describes how the surface morphology can be controlled by the molecular structure of the copolymers (volume ratio between the sequences, molecular weight, length of the alkyl side group) and by the experimental conditions used for the preparation of the films. The molecular structure of the chains is fully determined by the synthesis of the copolymers via living anionic polymerization while the parameters that can be modified when preparing the samples are the nature of the solvent and the thermal annealing of the films. Finally, we report on a systematic comparison between images and approach-retract curve data. We show that this experimental comparison allows the origin of the contrast that produces the image to be straightforwardly evaluated. The method provides an unambiguous quantitative measurement of the contribution of the local mechanical response to the image. We show that most of the contrast in the height and phase images is due to variations in local mechanical properties and not in topography. [less ▲]

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See detailMicrophase separation at the surface of block copolymers, as studied with atomic force microscopy
Rasmont, A.; Leclère, Philippe; Doneux, C. et al

in Colloids and Surfaces B : Biointerfaces (2000), 19(4), 381-395

Atomic force microscopy (AFM) is used to study the phase separation process occurring in block copolymers in the solid state. The simultaneous measurement of the amplitude and the phase of the oscillating ... [more ▼]

Atomic force microscopy (AFM) is used to study the phase separation process occurring in block copolymers in the solid state. The simultaneous measurement of the amplitude and the phase of the oscillating cantilever in the tapping mode operation provides the surface topography along with the cartography of the microdomains of different mechanical properties. This technique thus allows to characterize the size and shape of those microdomains and their organization at the surface (e.g. cubic lattice spheres, hexagonal lattice of cylinders, or lamellae). In this study, a series of symmetric triblock copolymers made of a inner elastomeric sequence (poly(butadiene) or poly(alkylacrylate)) and two outer thermoplastic sequences (poly(methylmethacrylate)) is analyzed by AFM in the tapping mode. The microphase separation and their morphology are essential factors for the potential of these materials as a new class of thermoplastic elastomers. Special attention is paid to the control of the surface morphology, as observed by AFM, by the molecular structure of the copolymers (volume ratio of the sequences, molecular weight, length of the alkyl side group) and the experimental conditions used for the sample preparation. The molecular structure of the chains is completely controlled by the synthesis, which relies on the sequential living anionic polymerization of the comonomers. The copolymers are analyzed as solvent-cast films, whose characteristics depend on the solvent used and the annealing conditions. The surface arrangement of the phase-separated elastomeric and thermoplastic microdomains observed on the AFM phase images is discussed on the basis of quantitative information provided by the statistical analysis by Fourier transform and grain size distribution calculations. [less ▲]

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See detailMorphology and rheology of poly(methyl methacrylate)-block-poly(isooctyl acrylate)-block-poly(mehtyl methacrylate) triblock copolymers, and potential as thermoplastic elastomers
Tong, Jiang-Dong; Leclère, Philippe; Rasmont, A. et al

in Macromolecular Chemistry and Physics (2000), 201(12), 1250-1258

The phase morphology and rheological properties of a series of poly(methyl methacrylate)-block-poly(isooctyl acrylate)-block-poly(methyl methacrylate) triblock copolymers (MIM) have been studied. These ... [more ▼]

The phase morphology and rheological properties of a series of poly(methyl methacrylate)-block-poly(isooctyl acrylate)-block-poly(methyl methacrylate) triblock copolymers (MIM) have been studied. These copolymers have well-defined molecular structures, with a molecular weight (MW) of poly(methyl methacrylate) (PMMA) in the range of 3 500-50 000 and MW of poly(isooctyl acrylate) (PIOA) ranging from 100 000 to 140 000. Atomic force microscopy with phase detection imaging has shown a two-phase morphology for all the MIM copolymers. The typical spherical, cylindrical, and lamellar phase morphologies have been observed depending on the copolymer composition. MIM consisting of very short PMMA end blocks (MW 3 500-5 000) behave as thermoplastic elastomers (TPEs), with however an upper-service temperature higher than the traditional polystyrene-block-polyisoprene-block-polystyrene TPEs (Kraton D1107). A higher processing temperature is also noted, consistent with the higher viscosity of PMMA compared to PS. [less ▲]

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See detailSynthesis and bulk properties of poly(methyl methacrylate)-b-poly(isooctyl acrylate(isooctyl acrylate)-b-poly(methyl methacrylate)
Tong, J. D.; Leclère, Philippe; Doneux, C. et al

in Polymer (2000), 41(12), 4617-4624

A series of well-defined poly(methylmethacrylate) (PMMA)-b-poly(isooctylacrylate) (PIOA)-b-PMMA triblock copolymers (MIM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate) (PtBA ... [more ▼]

A series of well-defined poly(methylmethacrylate) (PMMA)-b-poly(isooctylacrylate) (PIOA)-b-PMMA triblock copolymers (MIM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate) (PtBA)-b-PMMA precursors (MTM) by isooctyl alcohol. Phase separation is observed for all the investigated triblock copolymers, thus containing PMMA outer blocks in the 3500-50,000 molecular weight (MW) range and PIOA inner block with MW in the 100,000-300,000 range. The ultimate tensile properties of these MIM triblock copolymers are poor even when PMMA blocks of 50,000 MW are associated with an inner PIOA block of 300,000 MW. A reasonable explanation should be found in the molecular weight between chain entanglements (Me), which has been estimated at 60,000 for PIOA, much higher than Me for the traditional polydiene central blocks in the well-known thermoplastic elastomers of the triblock type. The tensile behavior of MIM copolymers has been successfully accounted for by a simple elastomer model free from chain entanglements, supporting the view that the lack of entanglements in the central block is very detrimental to the mechanical properties of the investigated fully (meth)acrylate triblock copolymers. [less ▲]

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See detailNovel functionalized oligo-vinylthiophene molecules with modulated second-order nonlinear optical response
dos Santos, D. A.; Kogej, T.; Brédas, Jean-Luc et al

in Journal of Molecular Structure (2000), 521

We present a joint theoretical and experimental investigation of the second-order nonlinear optical properties of a new kind of active molecule with a triblock structure. The molecular architecture is ... [more ▼]

We present a joint theoretical and experimental investigation of the second-order nonlinear optical properties of a new kind of active molecule with a triblock structure. The molecular architecture is such that two highly polarizable conjugated segments are separated from each other by a spacer; one of the conjugated segments is end-capped with an electron-donor group, the other one by an acceptor. E-vinylthiophenes are used as the conjugated segments; N,N-dimethylaniline and nitrophenyl are selected as the donor-acceptor pairs, while the spacer consists of a nonconjugated moiety. Several spacers are considered and discussed with respect to their ability to modulate the charge transfer between the donor and acceptor ends. [less ▲]

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See detailSynthesis, morphology, and mechanical properties of poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly (methyl methacrylate) triblocks. Ligated anionic polymerization vs atom transfer radical polymerization
Tong, Jiang-Dong; Moineau, Georges; Leclère, Philippe et al

in Macromolecules (2000), 33(2), 470-479

Poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) triblock copolymers have been prepared by ligated anionic polymerization (LAP; 8K-50K-8K) and atom transfer radical ... [more ▼]

Poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) triblock copolymers have been prepared by ligated anionic polymerization (LAP; 8K-50K-8K) and atom transfer radical polymerization (ATRP; 9K-51K-9K). Size exclusion chromatography, nuclear magnetic resonance, and differential scanning calorimetry have confirmed that the molecular structure of the two triblock copolymers is essentially identical. However, important differences are found in dynamic mechanical properties, viscoelastic properties, and stress−strain behavior. Indeed, the ATRP copolymer has low storage modulus, high complex viscosity, high order−disorder transition temperature, and poor ultimate tensile strength and elongation at break, compared to those of the LAP analogue. Marked differences also observed by tapping mode atomic force microscopy in the microscopic morphology of thin films of these copolymers. All these observations can be explained by the slow initiation of MMA by the poly(n-butyl acrylate) macroinitiator used in ATRP in contrast to what happens when MMA is added to living poly(tert-butyl acrylate) anions. As a result, the polydispersity of the short poly(methyl methacrylate) (PMMA) outer blocks is much broader in the ATRP copolymer, although the polydispersity index of the triblock is only 1.15. This heterogeneous structure of the ATRP triblock is also supported by the comparison of homo-PMMAs prepared by LAP and ATRP. [less ▲]

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See detailDirect observation of microdomain morphology in "all-acrylic" thermoplastic elastomers synthesized via living radical polymerization
Leclère, Philippe; Moineau, Georges; Minet, Michaël et al

in Langmuir (1999), 15(11), 3915-3919

We investigate the microscopic morphology of thin films of symmetric triblock copolymers synthesized via a two-step “living” radical polymerization of n-butylacrylate and methyl methacrylate. These ... [more ▼]

We investigate the microscopic morphology of thin films of symmetric triblock copolymers synthesized via a two-step “living” radical polymerization of n-butylacrylate and methyl methacrylate. These copolymers with low poly(methyl methacrylate) contents constitute a new class of potential thermoplastic elastomers with higher service temperature and oxidation resistance compared to conventional polydiene−polystyrene-based thermoplastic elastomers. The straightforward synthetic pathway allows for strict control of molecular weight, molecular-weight distribution, and composition. The presence in the copolymer of immiscible segments covalently bound to each other leads to phase separation on the nanometer scale. Regular organization of the phase-separated nanodomains is observed in real space by scanning force microscopy. The data point to a strong contrast in the local mechanical properties, corresponding to the microphase morphology. Cylinders of the minority phase are found to orient perpendicular to the surface, because of the surface energy difference between the constituents. Lamellae are also arranged perpendicular to the surface, in contrast to what is usually observed in block copolymers. This particular orientation is thought to result from the symmetric character of these triblock systems, with the outer blocks more polar than the central sequence. [less ▲]

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See detailControlling the electrografting of polymers onto transition metal surfaces through solvent vs monomer adsorption
Crispin, Xavier; Lazzaroni, Roberto; Geskin, Victor et al

in Journal of the American Chemical Society (1999), 121(1), 167-187

Electropolymerization of methacrylic monomers opens the possibility of chemically grafting a wide range of polymers onto transition metal surfaces. In this work, the electropolymerization of ... [more ▼]

Electropolymerization of methacrylic monomers opens the possibility of chemically grafting a wide range of polymers onto transition metal surfaces. In this work, the electropolymerization of polyacrylonitrile and polyethyl acrylate is studied in different solvents; we experimentally confirm that the choice of solvent is a critical parameter for obtaining electrografted polymers. A density-functional theory−based study modeling the interaction of solvent (acetonitrile, dimethylformamide, and pyridine) or monomer (acrylonitrile and ethyl acrylate) molecules with the Ni(100) metal surface provides the means to classify the organic molecules with respect to their ability to interact with the surface. The surface binding-energy difference between monomer and solvent is introduced in a Frumkin-type isotherm. This allows us to rationalize the experimental observations in terms of a competitive adsorption at the metal surface between the monomer and the solvent. The first step in the electrografting mechanism thus appears to be the chemisorption of the monomer at the electrode surface before cathodic polarization is applied; the chemisorbed monomer is therefore the first species reduced, giving rise to an adsorbed reactive intermediate, which is thus able to start the polymerization of a grafted chain. [less ▲]

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See detailStructure-second-order polarizability relationship in chromophores incorporating a spacer: a joint experimental and theoretical study
Maertens, Christophe; Detrembleur, Christophe ULg; Dubois, Philippe ULg et al

in Chemistry : A European Journal (1999), 5(1), 369-380

A joint theoretical and experimental study is reported on the structure-polarizability relationship in a novel type of push-pull conjugated system which contains a spacer within the conjugated backbone ... [more ▼]

A joint theoretical and experimental study is reported on the structure-polarizability relationship in a novel type of push-pull conjugated system which contains a spacer within the conjugated backbone. The chromo-phores are based on a dithienyl conjugation pathway, spaced by a keto group, and selectively end-capped by a donor and an acceptor. Four chromophores were synthesized, in which the strength of the acceptor group and the length of the conjugated path were varied. The electronic properties of two model compounds were studied theoretically by means of correlated quantum-chemical calculations. The degree of ground-state polarization was varied in the calculations by the application of an external electric field and varied experimentally by the modification of the dielectric constant of a binary mixture of solvents. The linear and nonlinear optical properties of the compounds (measured in solution by hyper-Rayleigh scattering) are discussed in detail. [less ▲]

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See detailA novel biodegradable and biocompatible ceramer prepared by the sol-gel process
Tian, Dong; Dubois, Philippe ULg; Grandfils, Christian ULg et al

in Chemistry of Materials (1997), 9(4), 871-874

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See detailElectrochemical synthesis of new electroactive polymers from dithienylene-vinylene derivatives
Jérôme, Christine ULg; Maertens, Christophe; Mertens, Marc et al

in Synthetic Metals (1997, January), 84(1-3), 163-164

Highly conjugated thiophene derivatives, based on thienylene-vinylene and thieneylene-vinylene-phenylene units, have been synthesized in order to examine: (i) the effect of such regular conjugated monomer ... [more ▼]

Highly conjugated thiophene derivatives, based on thienylene-vinylene and thieneylene-vinylene-phenylene units, have been synthesized in order to examine: (i) the effect of such regular conjugated monomer structures on the polymerization; (ii) the optical and electrochemical properties of the corresponding conjugated polymers. The all-trans monomers have been prepared by a Wittig reaction and the polymers have then been synthesized electrochemically. The polymers are electrochromic and can be reversibly doped both oxidatively and reductively. Their electrochemical behavior and optical properties have been analysed on the basis of quantum-chemical calculations. [less ▲]

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See detailCarbon black-filled polymer blends : a scanning probe microscopy characterization
Leclère, Philippe; Lazzaroni, Roberto; Gubbels, Frédéric et al

in Materials Research Society Symposium Proceedings (1997), 457

Conducting polymer composites, that consist of a conducting filler randomly distributed throughout an insulating polymer or polymer blend, attract interest in several application fields such as sensors or ... [more ▼]

Conducting polymer composites, that consist of a conducting filler randomly distributed throughout an insulating polymer or polymer blend, attract interest in several application fields such as sensors or electromagnetic radiation shielding. The macroscopic electrical resistivity of the filled polyblend strongly depends on the localization of the filler. Here, we investigate the morphology of Carbon Black (CB)-filled polymer blends in order to determine the parameters governing the selective localization of CB in one phase of the blend components or at the interface between the components. The dispersion of the CB particles in the polymer blend is observed by means of Lateral Force Microscopy (LFM) as a function of the blend composition and the load in CB. The selective localization of CB at the interface enables the reduction of the percolation threshold down to 0.5 wt%; as a result, the mechanical properties of the polymer blend can be fully retained. Different techniques can be used to locate the CB at the interface; we compare their efficiency experimentally. [less ▲]

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See detailElectrochemical synthesis and characterization of the electronic structure of new conjugated polymers from dithienylene vinylene derivatives
Jérôme, Christine ULg; Maertens, Christophe; Mertens, Marc et al

in Synthetic Metals (1996), 83(2), 103-109

Highly conjugated thiophene derivatives, based on thienylene vinylene and thienylene vinylene phenylene units, have been synthesized in order to examine: (i) the effect of such regular conjugated monomer ... [more ▼]

Highly conjugated thiophene derivatives, based on thienylene vinylene and thienylene vinylene phenylene units, have been synthesized in order to examine: (i) the effect of such regular conjugated monomer structures on polymer formation; and (ii) the optical and electrochemical properties of the corresponding macromolecules. The all-trans monomers have been prepared by a Wittig reaction. The polymers have then been synthesized electrochemically. The polymers are electrochromic and can be reversibly doped both oxidatively and reductively. Their electrochemical behavior and optical properties have been analyzed on the basis of a series of quantum-chemical calculations. [less ▲]

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See detailMicrodomain morphology analysis of block copolymers by atomic force microscopy with phase detection imaging
Leclère, Philippe; Lazzaroni, Roberto; Brédas, Jean-Luc et al

in Langmuir (1996), 12(18), 4317-4320

We use atomic force microscopy (AFM) with phase detection imaging (PDI) in order to study the surface microdomain morphology of thick (i.e., ca. 2 mm) films of triblock copolymers. We present here the ... [more ▼]

We use atomic force microscopy (AFM) with phase detection imaging (PDI) in order to study the surface microdomain morphology of thick (i.e., ca. 2 mm) films of triblock copolymers. We present here the results obtained on a poly(methyl methacrylate)-block-polybutadiene-block-poly(methyl methacrylate) (PMMA-b-PBD-b-PMMA) copolymer prepared by using a 1,3-diisopropenylbenzene (DIB)-based difunctional anionic initiator. Our data illustrate the interest of PDI for the elucidation of surface phase separation in block copolymers. We show that the surface of thick films studied by this new technique exhibits a two-phase structure corresponding to the two types of components. [less ▲]

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See detailA combined theoretical and experimental study of the electrochemically induced chemisorption of acrylonitrile on nickel, copper, and zinc
Fredriksson, C.; Lazzaroni, Roberto; Brédas, Jean-Luc et al

in Chemical Physics Letters (1996), 258(3-4), 356-362

We report a combined theoretical and experimental study of the interaction between a series of transition metals (Ni, Cu, Zn) and acrylonitrile. We demonstrate experimentally that the transition metal has ... [more ▼]

We report a combined theoretical and experimental study of the interaction between a series of transition metals (Ni, Cu, Zn) and acrylonitrile. We demonstrate experimentally that the transition metal has a selective role in the grafting of electropolymerized acrylonitrile. Nickel and copper substrates support the formation of a polyacrylonitrile film, while zinc does not. Quantum chemical calculations indicate that acrylonitrile molecules form π-d bonds with Ni and Cu atoms, but do not react chemically with a Zn atom, in qualitative agreement with the experiment. Computational results also show that the electron affinity is significantly increased upon chemisorption, promoting radical anion species at the metal surface as initiators for polymerization. [less ▲]

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See detailTheoretical investigation of the molecular structure of aluminium triisopropoxide and its complexes in ring-opening polymerization
Parenté, Vincent; Brédas, Jean-Luc; Dubois, Philippe ULg et al

in Macromolecular Theory and Simulations (1996), 5(3), 525-546

We present a theoretical study on aluminium triisopropoxide (Al(O1Pr)3) using both empirical (Molecular Mechanics, MM, with Dreiding II force field) and quantum-chemical (Austin Model 1, AMI ... [more ▼]

We present a theoretical study on aluminium triisopropoxide (Al(O1Pr)3) using both empirical (Molecular Mechanics, MM, with Dreiding II force field) and quantum-chemical (Austin Model 1, AMI, semiempirical Hartree-Fock) techniques. We determine the most stable geometries for both the tetramer and tiimer of aluminium triisopropoxide as well as the thermodynamic characteristics of the equilibrium existing between these two aggregated structures. The theoretical results are compared to experimental data from X-ray diffraction and 27Al NMR measurements. For the tetramer, it appears that the optimal equilibrium geometries are in good agreement with the experimental X-ray diffraction geometry; another geometry is also obtained with both theoretical approaches, which is slightly less stable but of higher symmetry. On the basis of the most stable configurations for the tetramer and trimer aggregates, the variation of free enthalpy (AG) between the two aggregated structures has been estimated. The evolution of the theoretical AG values indicates a displacement of equilibrium towards the trimer species with temperature, in good agreement with experimental 1H and 27Al NMR data. Moreover, the AMI heats of formation show a gain of 33.9 kcal/mol due to the aggregation of four Al(O1Pr)3 instead of three, and thus a better stability of the tetramer. The molecular geometries being well described by the theoretical methods used in this study, we also present a model for the ring-opening polymerization complexes of ε-caprolactone and lactides. [less ▲]

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