References of "Dubois, Philippe"
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See detailIntercalative polymerization of cyclic esters in layered silicates : thermal vs. catalytic activation
Pantoustier, Nadège; Alexandre, Michaël ULg; Degée, Philippe et al

in Composite Interfaces (2003), 10(4-5), 423-433

Poly(ε-caprolactone) layered silicate nanocomposites were synthesized by in situ inter-calative ring-opening polymerization (ROP) of ε-caprolactone. The polymerization was promoted by thermal or catalytic ... [more ▼]

Poly(ε-caprolactone) layered silicate nanocomposites were synthesized by in situ inter-calative ring-opening polymerization (ROP) of ε-caprolactone. The polymerization was promoted by thermal or catalytic initiation starting from either non-modified natural sodium-montmorillonite (MMT-Na) or montmorillonite modified by different ammonium cations bearing either non-functional alkyl chains or chains terminated by carboxylic acid or hydroxyl functions. The resulting compositions were analyzed by small-angle X-ray diffraction and transmission electron microscopy. The clay dispersion depended on the structure of the alkyl ammonium. Exfoliated nanocomposites were formed when hydroxyl-containing alkyl-ammonium was used; otherwise, partially intercalated/partially exfoliated structures were observed. Moreover, caving to the inherent catalytic properties of the montmo-rillomte surface, it was also possible to prepare intercalated nanocomposites by in situ polymerization of ε-caprolactone in presence of non-modified montmorillonite-Na (MMT-Na) without any added catalyst. [less ▲]

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See detailPoly(epsilon-caprolactone)/clay nanocomposites by in-situ intercalative polymerization catalyzed by dibutyltin dimethoxide
Lepoittevin, Bénédicte; Pantoustier, Nadège; Devalckenaere, Myriam et al

in Macromolecules (2002), 35(22), 8385-8390

Poly(epsilon-caprolactone)/clay nanocomposites were prepared by in-situ ring-opening polymerization of epsilon-caprolactone by using dibutyltin dimethoxide as an initiator/catalyst. A nonmodified Na ... [more ▼]

Poly(epsilon-caprolactone)/clay nanocomposites were prepared by in-situ ring-opening polymerization of epsilon-caprolactone by using dibutyltin dimethoxide as an initiator/catalyst. A nonmodified Na+-montmorillonite and two montmorillonites surface-modified by dimethyl 2-ethylhexyl (hydrogenated tallow alkyl) and methyl bis(2-hydroxyethyl) (hydrogenated tallow alkyl) ammonium cations, respectively, were used. The evolution of molecular weights was followed in relation to silicate surface modification and clay concentration. The alcohol-bearing organo-modified clay was a co-initiator for the polymerization reaction and thus controlled the molecular weight of the PCL chains. Furthermore, the number-average molecular weight of the growing PCL chains linearly increased with the monomer conversion. Nanocomposites were analyzed by small-angle X-ray diffraction, transmission electron microscopy, and thermogravimetry. The clay dispersion depended on the structure of the alkylammonium used to make the clay more hydrophobic. Exfoliated nanocomposites were formed when hydroxyl-containing alkylammonium. was used; otherwise, intercalated structures were reported. Thermogravimetric analyses showed a higher degradation temperature for the exfoliated structures than for the intercalated ones, both of them exceeding the degradation temperature of unfilled poly(epsilon-caprolactone). [less ▲]

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See detail2-oxepane-1,5-dione: A precursor of a novel class of versatile semicrystalline biodegradable (Co)polyesters
Latere, Jean-Pierre; Lecomte, Philippe ULg; Dubois, Philippe ULg et al

in Macromolecules (2002), 35(21), 7857-7859

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See detailBiodegradable polyester layered silicate nanocomposites based on poly(epsilon-caprolactone)
Pantoustier, Nadège; Lepoittevin, Bénédicte; Alexandre, Michaël ULg et al

in Polymer Engineering & Science (2002), 42(9), 1928-1937

Nanocomposites based on biodegradable poly(epsilon-caprolactone) (PCL) and layered silicates (montmorillonite, MMT) were prepared either by melt intercalation with PCL or by in situ ring-opening ... [more ▼]

Nanocomposites based on biodegradable poly(epsilon-caprolactone) (PCL) and layered silicates (montmorillonite, MMT) were prepared either by melt intercalation with PCL or by in situ ring-opening polymerization of epsilon-caprolactone as promoted by the so-called coordination-insertion mechanism. Both non-modified clays (Na+-MMT) and silicates modified by various alkylammonium cations were studied. Mechanical and thermal properties were examined by tensile testing and thermogravimetric analysis. Even at a filler content as low as 3 wt% of inorganic layered silicate, the PCL-layered silicate nanocomposites exhibited improved mechanical properties (higher Young's modulus) and increased thermal stability as well as enhanced flame retardant characteristics as a result of a charring effect. It was shown that the formation of PCL-based nanocomposites depended not only on the nature of the ammonium cation and related functionality but also on the selected synthetic route, melt intercalation vs. in situ intercalative polymerization. Interestingly enough, when the intercalative polymerization of epsilon-caprolactone was carried out in the presence of MMT organo-modified with ammonium cations bearing hydroxyl functions, nanocomposites with much improved mechanical properties were recovered. Those hybrid polyester layered silicate nanocomposites. were characterized by a covalent bonding between the polyester chains and the clay organo-surface as a result of the polymerization mechanism, which was actually initiated from the surface hydroxyl functions adequately activated by selected tin (II) or tin (IV) catalysts. [less ▲]

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See detailPoly(epsilon-caprolactone)/clay nanocomposites prepared by melt intercalation: mechanical, thermal and rheological properties
Lepoittevin, Bénédicte; Devalckenaere, Myriam; Pantoustier, Nadège et al

in Polymer (2002), 43(14), 4017-4023

(Nano)composites of poly(epsilon-caprolactone) (PCL) were prepared by melt blending the polymer with natural Na+ montmorillonite and montmorillonite modified by hydrogenated tallowalkyl (HTA)-based ... [more ▼]

(Nano)composites of poly(epsilon-caprolactone) (PCL) were prepared by melt blending the polymer with natural Na+ montmorillonite and montmorillonite modified by hydrogenated tallowalkyl (HTA)-based quaternary ammonium cations, such as dimethyl 2-ethylhexyl HTA ammonium and methyl bis(2-hydroxyethyl) HTA ammonium. Microcomposites or nanocomposites were prepared depending on whether neat or modified montmorillonites was used, as assessed by X-ray diffraction and transmission electron microscopy. Mechanical and thermal properties were studied as a function of the filter content by tensile testing, Izod impact testing, thermogravimetric analysis and differential scanning calorimetry. The rheological behaviour at 80 degreesC was also analysed in relation to the structure and content of the layered silicate. Effect of exfoliated silicates on the mechanical properties, thermal stability and flame resistance of PCL was considered. Stiffness and thermal stability improved with the filler loading until a content of 5 wt%. Further loading resulted in the levelling off and possibly in a decrease of these properties. A marked charring effect was observed upon exposure to a flame. [less ▲]

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See detailPolyethylene-layered silicate nanocomposites prepared by the polymerization-filling technique: synthesis and mechanical properties
Alexandre, Michaël ULg; Dubois, Philippe ULg; Sun, Tao et al

in Polymer (2002), 43(8), 2123-2132

Polyethylene-layered silicate nanocomposites were prepared by the in situ intercalative polymerization of ethylene by the so-called polymerization-filling technique and analyzed by transmission electron ... [more ▼]

Polyethylene-layered silicate nanocomposites were prepared by the in situ intercalative polymerization of ethylene by the so-called polymerization-filling technique and analyzed by transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), differential scanning calorimetry, dynamic mechanical analysis and tensile testing. Non-modified montmorillonite and hectorite were first treated by trimethylaluminum-depleted methylaluminoxane before being contacted by a Ti-based constrained geometry catalyst. The nanocomposite was formed by addition and polymerization of ethylene. In the absence of a chain transfer agent, ultra high molecular weight polyethylene was produced. The tensile properties of these nanocomposites were poor and essentially independent of the nature and content of the silicate. Upon hydrogen addition, the molecular weight of the polyethylene was decreased with parallel improvement of the tensile and shear moduli, in relation to the filler content. The exfoliation of the layered silicates was confirmed by XRD analysis and TEM observation. The mechanical kneading of the molten nanocomposites resulted in the partial collapse of the exfoliated structure driven by the thermodynamic stability of the layered filler. [less ▲]

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See detailPolyester layered silicate nanohybrids by controlled grafting polymerization
Lepoittevin, Bénédicte; Pantoustier, Nadège; Alexandre, Michaël ULg et al

in Journal of Materials Chemistry (2002), 12(12), 3528-3535

Poly( epsilon-caprolactone) (PCL) layered silicate nanohybrids were synthesized by ring opening polymerization of epsilon-caprolactone according to a well-controlled coordination-insertion mechanism ... [more ▼]

Poly( epsilon-caprolactone) (PCL) layered silicate nanohybrids were synthesized by ring opening polymerization of epsilon-caprolactone according to a well-controlled coordination-insertion mechanism. Montmorillonites were surface-modified by non functional (trimethylhexadecylammonium) and hydroxy functional alkylammonium cations, i.e., (2-hydroxyethyl) dimethylhexadecylammonium. The hydroxy functions available at the clay surface were activated into tin( II or IV) or Al(III) alkoxide initiators for lactone polymerization, thus yielding surface-grafted PCL chains. The surface-grafted PCL chains were recovered by an ionic exchange reaction with lithium chloride and they were analyzed by size exclusion chromatography. The PCL molar mass was measured as a function of the hydroxy content of the clay that was modulated by exchanging the Na cations with mixtures of non-functional and hydroxy functional ammonium cations of different compositions. Nanohybrids were also characterized by small-angle X-ray diffraction, transmission electron microscopy and thermogravimetry. The PCL molar mass and the nanocomposite morphology (i.e., exfoliation and/or intercalation) were readily tuned by the content of the hydroxy groups available at the clay surface. Surface-grafted aluminium trialkoxide species proved highly efficient in initiating polymerization that leads to PCL chains of controlled molar mass and narrow molecular weight distribution with polydispersity indices as low as 1.2. [less ▲]

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See detailMetallocene catalyzed polymerization of ethylene in the presence of graphite. 2. Structure and electrical properties of the composites
Pluta, Miroslaw; Alexandre, Michaël ULg; Blacher, Silvia ULg et al

in Polymer (2001), 42(22), 9293-9300

Structure and electrical properties of conducting polyethylene/graphite composites have been studied in relation to the preparation method, i.e. (i) the polymerization-filling technique (PFT), in which ... [more ▼]

Structure and electrical properties of conducting polyethylene/graphite composites have been studied in relation to the preparation method, i.e. (i) the polymerization-filling technique (PFT), in which the polyolefinic chains are growing from the graphite surface, (ii) the slurry polymerization of ethylene in the presence of untreated graphite, and (iii) the mechanical blending of preformed polyethylene and graphite. The extent of the filler dispersion depends on the method used for the composite preparation. Moreover, the graphite particles can be oriented by the molding of the samples used for the measurement of the electrical properties. This orientation is as pronounced as the melt viscosity of polyethylene is low, this characteristic feature changing with the preparation method. These structural details have consequences on the electrophysical properties and the percolation threshold. Finally, the thermal dependence of the electrical resistivity has been studied. [less ▲]

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See detailMetallocene catalyzed polymerization of ethylene in the presence of graphite. 1. Synthesis and characterization of the composites
Alexandre, Michaël ULg; Pluta, Miroslaw; Dubois, Philippe ULg et al

in Macromolecular Chemistry and Physics (2001), 202(11), 2239-2246

Polyethylene/graphite composites have been prepared by two different methods. In a first approach, the ethylene polymerization has been catalyzed by metallo-cene in the presence of neat graphite particles ... [more ▼]

Polyethylene/graphite composites have been prepared by two different methods. In a first approach, the ethylene polymerization has been catalyzed by metallo-cene in the presence of neat graphite particles (NGC composites). A second series of composites (TGC) has been prepared by the polymerization-filling technique, which requires that the metallocene/methylalumoxane catalyst is fixed onto the graphite surface prior to the ethylene polymerization. The two series of composites exhibit significantly different morphology and thermal properties. The filler distribution is very heterogeneous in the NGC series. The morphology changes from an intimate mixture of PE and filler particles at low graphite content to graphite covered by patches of PE at high filler loading. The graphite distribution is much more homogeneous in the TGC samples, and the morphology consists of particles covered by a layer of PE in the whole composition range. Differences in the thermal properties are discussed in relation to the morphology. [less ▲]

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See detailEffect of the Solvent Polarity on the Living Ligated Anionic Polymerization of tert-Butyl Methacrylate and Copolymerization with Methyl Methacrylate
Zune, Catherine; Archambeau, C.; Dubois, Philippe ULg et al

in Journal of Polymer Science. Part A, Polymer Chemistry (2001), 39(10), 1774-1785

An anionic polymerization of t-butyl methacrylate and a copolymerization with methyl methacrylate were initiated with an organolithium ligated with 10 equiv of LiCl. As a rule, the complexation of the ... [more ▼]

An anionic polymerization of t-butyl methacrylate and a copolymerization with methyl methacrylate were initiated with an organolithium ligated with 10 equiv of LiCl. As a rule, the complexation of the active species by LiCl masked the effect that the polarity of the solvent might have on the molecular structure of the chains. [less ▲]

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See detailPreparation and properties of layered silicate nanocomposites based on ethylene vinyl acetate copolymers
Alexandre, Michaël ULg; Beyer, Günter; Henrist, Catherine ULg et al

in Macromolecular Rapid Communications (2001), 22(8), 643-646

(Nano)composites based on ethylene vinyl acetate copolymers (EVA) and montmorillonite modified by various alkylammonium cations were processed by mechanical kneading. Polymer intercalation and filler ... [more ▼]

(Nano)composites based on ethylene vinyl acetate copolymers (EVA) and montmorillonite modified by various alkylammonium cations were processed by mechanical kneading. Polymer intercalation and filler exfoliation were evidenced by X-ray diffraction and transmission electron microscopy, respectively. Nano-composites tensile properties showed that Young's modulus increases significantly even at very low content of the organo-modified filler while preserving high ultimate elongation and tensile stress. The matrix thermal stability in air was increased by 40°C and, interestingly, the obtained nanocomposites present flame retardant properties. TEM micrograph of the nanocomposite based on EVA3 filled with 5 wt.-% of Mont-2CN2C18. [less ▲]

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See detailPolymerization-filling technique: an efficient way to improve the mechanical properties of polyethylene composites
Alexandre, Michaël ULg; Martin, Eric; Dubois, Philippe ULg et al

in Chemistry of Materials (2001), 13(2), 236-237

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See detailPoly (ε-caprolactone-b-glycolide) and Poly(D,L-lactide-b-glycolide) diblock copolyesters: controlled synthesis, characterization, and colloidal dispersions
Barakat, Ibrahim; Dubois, Philippe ULg; Grandfils, Christian ULg et al

in Journal of Polymer Science. Part A, Polymer Chemistry (2001), 39(2), 294-306

Living -aluminum alkoxide poly--caprolactone and poly-D,L-lactide chains were synthesized by the ring-opening polymerization of -caprolactone (-CL) and D,L-lactide (D,L-LA), respectively, and were used as ... [more ▼]

Living -aluminum alkoxide poly--caprolactone and poly-D,L-lactide chains were synthesized by the ring-opening polymerization of -caprolactone (-CL) and D,L-lactide (D,L-LA), respectively, and were used as macroinitiators for glycolide (GA) polymerization in tetrahydrofuran at 40 °C. The P(CL-b-GA) and P(LA-b-GA) diblock copolymers that formed were fractionated by the use of a selective solvent for each block and were characterized by 1H NMR spectroscopy and differential scanning calorimetry analysis. The livingness of the operative coordination-insertion mechanism is responsible for the control of the copolyester composition, the length of the blocks, and, ultimately, the thermal behavior. Because of the inherent insolubility of the polyglycolide blocks, microphase separation occurs during the course of the sequential polymerization, resulting in a stable, colloidal, nonaqueous copolymer dispersion, as confirmed by photon correlation spectroscopy. [less ▲]

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See detailPoly(e-caprolactone) layered silicate nanocomposites: effect of clay surface modifiers on the melt intercalation process
Pantoustier, Nadège; Alexandre, Michaël ULg; Degée, Philippe et al

in e-Polymers (2001), (9), 1-9

Nanocomposites based on biodegradable poly(e-caprolactone) (PCL) and layered silicates (montmorillonite) modified by various alkylammonium cations were prepared by melt intercalation. Depending on whether ... [more ▼]

Nanocomposites based on biodegradable poly(e-caprolactone) (PCL) and layered silicates (montmorillonite) modified by various alkylammonium cations were prepared by melt intercalation. Depending on whether the ammonium cations contain non-functional alkyl chains or chains terminated by carboxylic acid or hydroxyl functions, microcomposites or nanocomposites were recovered as shown by X-ray diffraction and transmission electron microscopy. Mechanical and thermal properties were examined by tensile testing and thermogravimetric analysis. The layered silicate PCL nanocomposites exhibited some improvement of the mechanical properties (higher Young's modulus) and increased thermal stability as well as enhanced flame retardant characteristics as result of a charring effect. This communication aims at reporting that the formation of PCL-based nanocomposites strictly depends on the nature of the ammonium cation and its functionality, but also on the selected synthetic route, i.e. melt intercalation vs. in situ intercalative polymerization. Typically, protonated w-aminododecanoic acid exchanged montmorillonite allowed to intercalate e-caprolactone monomer and yielded nanocomposites upon in situ polymerization, whereas they exclusively formed microcomposites when blended with preformed PCL chains. In other words, it is shown that the formation of polymer layered silicate nanocomposites is not straightforward and cannot be predicted since it strongly depends on parameters such as ammonium cation type and functionality together with the production procedure, i.e., melt intercalation, solvent evaporation or in situ polymerization [less ▲]

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See detailPolarization holography reveals the nature of the grating in polymers containing azo-dye
Blanche, Pierre-Alexandre ULg; Lemaire, P. C.; Maertens, Christophe et al

in Optics Communications (2000), 185(1-3), 1-12

To study the origin of reversible holographic recording in three polymers containing the same azo-dye, we have measured the diffraction efficiency and analyzed the gratings characteristics for various ... [more ▼]

To study the origin of reversible holographic recording in three polymers containing the same azo-dye, we have measured the diffraction efficiency and analyzed the gratings characteristics for various writing beams polarizations. The amplitude of the holographic grating, as well as the ratio between index and absorption modulations, have been investigated by gratings shifting. The total amount of diffracted power and the diffraction efficiency versus the reading beam polarization has been measured by non-degenerated four waves mixing. These experiments have revealed that the molecular mechanisms of holographic recording in the studied compounds are different. The photoinduced orientation of the chromophores is predominant for C6-C11-DMNPAA; so, in C11-C6-DMNPAA (DMNPAA: 2,5-dimethyl-4-(p-nitrophenylazo)anisole), the refractive index variation comes from the presence of both trans and cis populations generated by photoisomerization. The behavior of the PVK:DMNPAA is included between these extreme cases since both phenomena act. [less ▲]

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See detailUse of metallocenes in the polymerization-filling technique with production of polyolefin-based composites
Alexandre, Michaël ULg; Martin, Eric; Dubois, Philippe ULg et al

in Macromolecular Rapid Communications (2000), 21(13), 931-936

In an updated version of the polymerization-filling technique, the surface of particulate fillers has been activated by metallocenes. Homogeneously filled polyolefins have accordingly been produced by the ... [more ▼]

In an updated version of the polymerization-filling technique, the surface of particulate fillers has been activated by metallocenes. Homogeneously filled polyolefins have accordingly been produced by the in situ copolymerization of ethylene and α-olefins, e.g., 1-octene and 1,9-decadiene. Different fillers have been successfully used, including inorganic particles with either an acidic surface (kaolin, glass beads, silica) or a basic surface (magnesium hydroxide, wollastonite), graphite and nickel particles. Hydrogen has proved to be efficient in reducing the molecular weight of the produced polymers. [less ▲]

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See detailPhotoinduced birefringence and diffraction efficiency in azo dye doped or grafted polymers: theory versus experiment of the temperature influence
Blanche, Pierre-Alexandre ULg; Lemaire, P. C.; Maertens, Christophe et al

in Journal of the Optical Society of America. B, Optical Physics (2000), 17(5), 729-740

We have investigated the influence of the temperature on the photoinduced birefringence as well as on the diffraction efficiency of azo dye doped or grafted polymers. The samples are composed of three ... [more ▼]

We have investigated the influence of the temperature on the photoinduced birefringence as well as on the diffraction efficiency of azo dye doped or grafted polymers. The samples are composed of three polymer matrices containing 2, 5-dimethyl-4-(p-nitrophenylazo anisole). We propose two theoretical models to explain the experimental increase of both phenomena when the temperature is decreased. Models are based on the statistical angular distribution of the chromophores that depends on the intensity of the polarized laser beam in the media, counteracted by the thermal agitation. Parameters introduced in both models can be used to characterize the polymeric system properties. [less ▲]

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See detailSingle-step reactive extrusion of PLLA in a corotating twin-screw extruder promoted by 2-ethylhexanoic acid tin(II) salt and triphenylphosphine
Jacobsen, S.; Fritz, H. G.; Degée, Philippe et al

in Polymer (2000), 41(9), 3395-3403

The ring opening polymerisation of L,L-lactide using an equimolar complex of 2-ethylhexanoic acid tin(II) salt Sn(Oct)2 and triphenylphosphine P( )3 as catalyst shows for the first time a reactivity ... [more ▼]

The ring opening polymerisation of L,L-lactide using an equimolar complex of 2-ethylhexanoic acid tin(II) salt Sn(Oct)2 and triphenylphosphine P( )3 as catalyst shows for the first time a reactivity providing a polymerisation propagation rate fast enough to imagine a continuous single-step reactive extrusion process for bulk polymerisation. The ring opening polymerisation has been realised on a corotating closely intermeshing twin-screw extruder, using a specially designed screw concept to provide sufficient energy input and mixing for further enhancement of the propagation rate, without detrimentally enhancing depolymerisation or transesterification reactions. Using one chosen screw and processing concept on a twin-screw extruder with 25 mm diameter and a L/D-ratio of 48, the influence of different processing parameters on the resulting molecular parameters of the Polylactide (PLA) has been determined. Furthermore, the mechanical property profile of the generated PLA-polymers is discussed and related to the molecular parameters. [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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