References of "Dubois, Philippe"
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See detailControlled ring-opening polymerization of epsilon-caprolactone promoted by "in situ" formed yttrium alkoxides
Martin, Eric; Dubois, Philippe ULg; Jérôme, Robert ULg

in Macromolecules (2000), 33(5), 1530-1535

The ring-opening polymerization of ε-caprolactone has been initiated by [tris(hexamethyldisilyl)amide]yttrium in the presence of an excess of 2-propanol. This initiating system is very active even at high ... [more ▼]

The ring-opening polymerization of ε-caprolactone has been initiated by [tris(hexamethyldisilyl)amide]yttrium in the presence of an excess of 2-propanol. This initiating system is very active even at high alcohol-to-Y molar ratio. Polymers with controlled molecular parameters (Mn, end groups) and low dispersity are formed as result of fast alkoxide/alcohol exchange. At molar excess of 2-propanol higher than 100, this exchange is no longer quantitative. The in situ formed active species involved in this new initiating system are different from those ones present in the commercial yttrium oxo-isopropoxide Y5(μ-O)(OiPr)13 cluster. Evidence is provided by 1H NMR spectroscopy. [less ▲]

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See detailRing opening copolymerization of ε-caprolactone, γ-(triethylsilyloxy)-ε-caprolactone and γ-ethylene ketal-ε-caprolactonelactone: a route to hetero-graft copolyesters
Stassin, Fabrice; Halleux, Olivier; Dubois, Philippe ULg et al

in Macromolecular Symposia (2000), 153

ε-Caprolactone (ε-CL) has been copolymerized with two precursors of γ-hydroxy-ε-CL, i.e., γ-ethylene ketal-ε-caprolactone (TOSUO) and γ-(triethylsilyloxy)-ε-caprolactone (TeSCL). The triethylsilyloxy ... [more ▼]

ε-Caprolactone (ε-CL) has been copolymerized with two precursors of γ-hydroxy-ε-CL, i.e., γ-ethylene ketal-ε-caprolactone (TOSUO) and γ-(triethylsilyloxy)-ε-caprolactone (TeSCL). The triethylsilyloxy pendant groups can be selectively deprotected into hydroxyl groups followed by the deprotection of the acetal substituents. Each series of hydroxyl groups can be used to initiate the polymerization of cyclic monomers so leading to hetero-graft copolyesters with, for instance, poly-ε-CL and polylactide grafts. [less ▲]

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See detailContinuous reactive extrusion polymerization of L-lactide - an engineering view
Jacobsen, Sven; Fritz, Hans-Gerhard; Degée, Philippe et al

in Macromolecular Symposia (2000), 153

Polylactides (PLA), biodegradable aliphatic polyesters, produced from renewable resources might substitute petrochemically based polymers in a broad range of applications in the near future, if we manage ... [more ▼]

Polylactides (PLA), biodegradable aliphatic polyesters, produced from renewable resources might substitute petrochemically based polymers in a broad range of applications in the near future, if we manage to produce them at lower cost and higher efficiency than nowadays. Possible applications include food packaging for meat and soft drinks, films for agro-industry and non-wovens in hygienic products. The authors developed, based on a new catalytic system, a reactive extrusion polymerisation process, which can be used to produce PLA continuously in larger quantities and at lower costs than before. This extrusion polymerisation process has been developed and tested with laboratory scale machines and has to be transferred to industrial processing equipment. This paper aims to address the problems attached with this transfer and to discuss the chances to finally achieve low cost PLA at industrial scale. [less ▲]

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See detailSynthesis and polarized light-induced birefringence of new polymethacrylates containing carbazolyl and azobenzene pendant groups
Maertens, Christophe; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Journal of Polymer Science. Part B, Polymer Physics (2000), 38(1), 205-213

Low Tg copolymers of [11(N-carbazolyl)undecylmethacrylate] and [2,5-dimethylphenyl-[(4-nitrophenyl)azo]-phenoxyalkylmethacrylate] have been synthesized and the polarized light-induced birefringence of ... [more ▼]

Low Tg copolymers of [11(N-carbazolyl)undecylmethacrylate] and [2,5-dimethylphenyl-[(4-nitrophenyl)azo]-phenoxyalkylmethacrylate] have been synthesized and the polarized light-induced birefringence of thick films (70 m) has been investigated at a constant deducted temperature relative to Tg (T - Tg = 10 °C). The optical properties of these copolymers have been studied in relation to the azo-dye content and the length of the alkyl spacer between the azo-dye and the methacrylic backbone. They have been compared with the dispersion of (4-methoxy-2,5-dimethylphenyl)-(4-nitrophenyl)diazene (DMNPAA) within a poly[11(N-carbazolyl)undecyl-methacrylate] and a poly[N-vinylcarbazole] (PVK) matrix. The experimental curves have been fitted by biexponentials, so emphasizing the effects of the copolymer structure on the kinetics of the writing process. The photoinduced orientation is more than three orders of magnitude higher in a grafted material compared to the dispersion version. The azo-dye concentration also has an important role in both the amplitude and the dynamics of the photo-orientation. [less ▲]

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See detailPolymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials
Alexandre, Michaël ULg; Dubois, Philippe ULg

in Materials Science & Engineering. R: Reports (2000), R28(1-2), 1-63

A review with 115 refs. This review aims at reporting on very recent developments in syntheses, properties and (future) applications of polymer-layered silicate nanocomposites. This new type of materials ... [more ▼]

A review with 115 refs. This review aims at reporting on very recent developments in syntheses, properties and (future) applications of polymer-layered silicate nanocomposites. This new type of materials, based on smectite clays usually rendered hydrophobic through ionic exchange of the sodium interlayer cation with an onium cation, may be prepd. via various synthetic routes comprising exfoliation adsorption, in situ intercalative polymn. and melt intercalation. The whole range of polymer matrixes is covered, i.e., thermoplastics, thermosets and elastomers. Two types of structure may be obtained, namely intercalated nanocomposites where the polymer chains are sandwiched in between silicate layers and exfoliated nanocomposites where the sepd., individual silicate layers are more or less uniformly dispersed in the polymer matrix. This new family of materials exhibits enhanced properties at very low filler level, usually inferior to 5 wt.%, such as increased Young's modulus and storage modulus, increase in thermal stability and gas barrier properties and good flame retardancy. [on SciFinder (R)] [less ▲]

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See detailNew catalysis for fast bulk ring-opening polymerization of lactide monomers
Degée, Philippe; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Macromolecular Symposia (1999), 144

The ring-opening polymerization of lactides has been studied in bulk using either 2-ethylhexanoic acid tin(II) salt, Sn(Oct)2, or aluminum triisopropoxide, Al(OiPr)3, as the initiator over a wide range of ... [more ▼]

The ring-opening polymerization of lactides has been studied in bulk using either 2-ethylhexanoic acid tin(II) salt, Sn(Oct)2, or aluminum triisopropoxide, Al(OiPr)3, as the initiator over a wide range of temperature and monomer-to-initiator molar ratio, A high increase in the bulk polymerization rate has been observed when the initiator was added with an equimolar amount of a Lewis base, such as triphenylphosphine and 4-picoline (C6H7N) added to Sn(Oct)2 and Al(OiPr)3, respectively Melt stable polylactides of high molecular weight and reasonably narrow molecular weight distribution have been accordingly prepared. The use of the Sn(Oct)2. equimolar combination has allowed for reaching an acceptable balance between propagation and depolymerization rates, so that the polymerization is fast enough to be performed through a continuous single-stage process in a twin-screw extruder A global activation mechanism is proposed and discussed by comparison with both investigated initiation systems. [less ▲]

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See detailStudy of the propagation center in the anionic polymerization of (meth)acrylic monomers: NMR study of Di-tert-butyl 2-Lithio-2.4'-trimethylglutarate and living poly(tert-butyl methacrylate) oligomers in THF/toluene mixtures
Zune, Catherine; Dubois, Philippe ULg; Grandjean, Jean ULg et al

in Macromolecules (1999), 32(7), 5477-5486

Solvation influences both the stereoregularity and molecular weight distribution (MWD) of poly(tert-butyl methacrylate) (PtBMA) prepared by anionic polymerization of tBMA with a lithium counterion in THF ... [more ▼]

Solvation influences both the stereoregularity and molecular weight distribution (MWD) of poly(tert-butyl methacrylate) (PtBMA) prepared by anionic polymerization of tBMA with a lithium counterion in THF/toluene mixed solvents at −78 °C. As a probe of the structural changes of the propagating species, multinuclear 7Li, 1H, and 13C NMR analysis of di-tert-butyl 2-lithio-2,4,4‘-trimethylglutarate (a model dimer, A) and of short-length living PtBMA chains is reported and discussed. Whatever the system, the main structure of the lithium ester enolate in THF/toluene mixtures is similar to that one reported in THF. In the case of A and for toluene contents exceeding 50% v/v, partly organized pseudophases can additionally be detected in the 7Li NMR spectra, but they do not provide well-developed 1H and 13C NMR signals. The chemical shifts of 1H and 13C signals of A support the dimeric form of this model. An equilibrium between dimeric and nonaggregated living PtBMA chains has been previously proposed to dominate in pure THF. However, marked self-termination of low-molecular weight living oligomers prepared in THF/toluene mixtures can be observed at 263 K, in contrast to the stability observed in pure THF up to 298 K. Another contrasting feature is the broadening of the molecular weight distribution which can be explained by an aggregation process that stabilizes oligomers at the early stage of the anionic polymerization as supported by SEC-RI and SEC-UV eluograms. [less ▲]

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See detailMacromolecular engineering of polylactones and polylactides. XXV. Synthesis and characterization of bioerodible amphiphilic networks and their use as controlled drug delivery systems
Barakat, Ibrahim; Dubois, Philippe ULg; Grandfils, Christian ULg et al

in Journal of Polymer Science. Part A, Polymer Chemistry (1999), 37(14), 2401-2411

Well-defined ,-methacryloyl poly--caprolactone (PCL) and poly(d,l)-lactide P(D,L)LA dimacromonomers have been synthesized by living ring-opening polymerization of the parent monomers initiated by ... [more ▼]

Well-defined ,-methacryloyl poly--caprolactone (PCL) and poly(d,l)-lactide P(D,L)LA dimacromonomers have been synthesized by living ring-opening polymerization of the parent monomers initiated by diethylaluminum 2-hydroxyethylmethacrylate (Et2AlO(CH2)2OC(O)C(CH3)CH2) and terminated by reaction of the propagating Al alkoxide groups with methacryloyl chloride. These dimacromonomers have been copolymerized with a hydrophilic comonomer, i.e., 2-hydroxyethylmethacrylate, in bulk at 65°C by using benzoyl peroxide as a free-radical initiator. The swelling ability of the amphiphilic PHEMA/PCL or P(D,L)LA networks has been investigated in both aqueous and organic media. Effect of network composition and molecular weight of the dimacromonomer on the swelling kinetics and the equilibrium solvent uptake has been studied. Lipophilic dexamethasone acetate and the hydrophilic sodium phosphate counterpart have been incorporated into the amphiphilic gels and their release has been studied in relation to the gel characteristics. [less ▲]

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See detailRing-opening metathesis polymerization of new alpha-norbornenyl poly(epsilon-caprolactone) macromonomers
Mecerreyes, David; Dahan, Dahan; Lecomte, Philippe ULg et al

in Journal of Polymer Science. Part A, Polymer Chemistry (1999), 37(14), 2447-2455

Poly(epsilon-caprolactone) (PCL) macromonomers capped by a polymerizable norbornene end-group have been synthesized and (co)polymerized by ring-opening metathesis with formation of graft copolymers and ... [more ▼]

Poly(epsilon-caprolactone) (PCL) macromonomers capped by a polymerizable norbornene end-group have been synthesized and (co)polymerized by ring-opening metathesis with formation of graft copolymers and polymacromonomers. -Norbornenyl PCL macromonomers have been synthesized by ring opening polymerization (ROP) of epsilon-caprolactone (CL) initiated by 2-diethylaluminoxymethyl-5-norbornene. Copolymerization of these PCL macromonomers with norbornene and polymerizable derivatives has been catalyzed by the [RuCl2(p-cymene)]2 PCy3/(trimethylsilyl)diazomethane complex yielding a series of poly(norbornene)-graft-poly(epsilon-caprolactone) copolymers. These new graft copolymers have been characterized by a set of analytical methods, i.e., SEC, 1H-NMR, FTIR, DSC, and TGA. Furthermore, PCL macromonomers have been polymerized into high molecular weight comb chains of narrow molecular weight distribution (Mw/Mn = 1.10) within high yields (90%). [less ▲]

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See detailBeneficial effect of triphenylphosphine on the bulk polymerization of L,L-lactide promoted by 2-ethylhexanoic acid tin (II) salt
Degée, Philippe; Dubois, Philippe ULg; Jacobsen, S. et al

in Journal of Polymer Science. Part A, Polymer Chemistry (1999), 37(14), 2413-2420

The ring-opening polymerization of L,L-lactide has been studied in bulk using 2-ethylhexanoic acid tin (II) salt, Sn(Oct)2, as a catalyst over a wide range of temperature and monomer to Sn(Oct)2 molar ... [more ▼]

The ring-opening polymerization of L,L-lactide has been studied in bulk using 2-ethylhexanoic acid tin (II) salt, Sn(Oct)2, as a catalyst over a wide range of temperature and monomer to Sn(Oct)2 molar ratio. Although Sn(Oct)2 was known to initiate a fast polymerization, it is reported now that some Lewis bases, particularly triphenylphosphine (P()3), can increase further the polymerization rate, without any detrimental effect on the polylactide thermal stability. In order to optimize the balance between propagation and competing depolymerization reactions, the experimental conditions, i.e., temperature and concentration of Sn(Oct)2 and P()3 have been optimized. The up-scaling of the laboratory experiments to reactive extrusion has proved to be feasible, which demonstrates the efficiency of this catalytic system to produce polylactide in a continuous one-stage polymerization process. [less ▲]

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See detailSynthesis of dendritic-linear block copolymers by living ring-opening polymerization of lactones and lactides using dendritic initiators
Mecerreyes, David; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Journal of Polymer Science. Part A, Polymer Chemistry (1999), 37(13), 1923-1930

Polyether dendrons have been successfully used as macroinitiators for the living ring-opening polymerization (ROP) of lactones and lactides. A hydroxyl group located at the focal point of dendrimers of ... [more ▼]

Polyether dendrons have been successfully used as macroinitiators for the living ring-opening polymerization (ROP) of lactones and lactides. A hydroxyl group located at the focal point of dendrimers of different generations was transformed into diethyl aluminum alkoxides by reaction with triethyl aluminum. The dendritic aluminum alkoxides proved to be efficient macroinitiators for the living ROP of -caprolactone (CL), 1,4,8-trioxa(4,6)spiro[9]undecanone (TOSUO), D,L- and L,L-lactide. Formation of these block copolymers of unusual macromolecular architecture was supported by size exclusion chromatography and spectroscopy. The versatility of this synthetic approach allowed -functional dendrimer block-polyesters, such as macromonomer, and macromolecules with novel architectures, to be prepared. [less ▲]

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See detailAnionic polymerization of (meth)acrylic monomers: anionic polymerization of tert-butyl methacrylate in toluene
Zune, Catherine; Dubois, Philippe ULg; Jérôme, Robert ULg

in Polymer International (1999), 48(7), 565-570

The anionic polymerization of tBMA initiated by an organolithium compound in toluene at low temperature (-78 °C and 0 °C) has been revisited. Under these experimental conditions, no livingness is reported ... [more ▼]

The anionic polymerization of tBMA initiated by an organolithium compound in toluene at low temperature (-78 °C and 0 °C) has been revisited. Under these experimental conditions, no livingness is reported, consistently with formation of an important fraction of oligomers (Mn = 650). [less ▲]

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See detailSynthesis of novel polybutadiene-graft-poly(sodium methacrylate) amphiphilic copolymers as precursors for liquid crystalline graft copolymers
Gohy, Jean-François; Charlier, Christelle; Zhang, Jian-Xin et al

in Macromolecular Chemistry and Physics (1999), 200(7), 1630-2638

Well-defined polybutadiene-graft-poly(tert-butyl methacrylate) (PBD-g-PtBMA) copolymers were prepared by reaction of PtBMA chains end-capped with a tert-butyl 4-vinylbenzoate (tBVB) anion, with the ... [more ▼]

Well-defined polybutadiene-graft-poly(tert-butyl methacrylate) (PBD-g-PtBMA) copolymers were prepared by reaction of PtBMA chains end-capped with a tert-butyl 4-vinylbenzoate (tBVB) anion, with the selectively hydrosilylated 1,2-units of anionically synthesized PBD. Substitution of the tBVB anion for the anion of living PtBMA chains is required for the formation of the expected C-silylation product instead of the unstable O-silylation one. Subsequent hydrolysis of the poly(tert-butyl methacrylate) grafts followed by neutralization of the carboxylic acid groups by sodium hydroxide leads to amphiphilic polybuta-diene-graft-poly(sodium methacrylate) (PBD-g-PNaMA) graft copolymers. These copolymers form unimeric micelles in water, as observed by dynamic light scattering (DLS). Non-covalent liquid crystalline graft copo-lymers were prepared by cation exchange between PBD-g-PNaMA copolymers and an ammonium containing smectic mesogen. These copolymers form a smectic mesophase which is microphase separated from PBD. [less ▲]

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See detailPolylactide (PLA) – A new way of production
Jacobsen, Sven; Degée, Philippe; Fritz, Hans-Gerhard et al

in Polymer Engineering & Science (1999), 39(7), 1311-1319

Poly(lactide) (PLA), a biodegradable aliphatic polyester with excellent properties for different polymer applications, has been used mostly in the biomedical field, mainly because of its high price ... [more ▼]

Poly(lactide) (PLA), a biodegradable aliphatic polyester with excellent properties for different polymer applications, has been used mostly in the biomedical field, mainly because of its high price, resulting from expensive polymerization and purification techniques. Although this polymer can play a major role in future markets for biodegradable polymers, the current high price has to be reduced significantly to at least $4 US/kg. Therefore, this paper aims to partially review the polymerization techniques traditionally used in PLA synthesis and to propose new developments that enable us to produce these polymers by an innovative process for just a portion of the costs traditionally charged, using reactive extrusion techniques in a closely intermeshing co-rotating twin screw extruder. This paper gives an overview of attainable mechanical properties and future markets. [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 detailDynamics of the photo-induced orientation and relaxation of new polymethacrylates containing carbazolyl and azobenzene pendant groups
Maertens, Christophe; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Polymer International (1999), 48(3), 205-211

Polarized-light-induced birefringence has been investigated in copolymers of [-(N-carbazolyl)alkyl methacrylate] and [2,5-dimethylphenyl-[(4-nitrophenyl)azo]phenoxyalkyl methacrylate]. Optical properties ... [more ▼]

Polarized-light-induced birefringence has been investigated in copolymers of [-(N-carbazolyl)alkyl methacrylate] and [2,5-dimethylphenyl-[(4-nitrophenyl)azo]phenoxyalkyl methacrylate]. Optical properties of the side-chain copolymers have been compared with materials in which the azo-dye was merely dispersed in a poly[-(N-carbazolyl)alkyl methacrylate] matrix. Increasing the temperature of the film has a dramatic depressive effect on the maximum of photo-induced orientation near and above the glass transition temperature (Tg) region, while its effect was restricted under this temperature. Kinetics of the photo-orientation and the thermal relaxation as a function of temperature have been analysed by a biexponential model based on two rate constants. The universal Williams-Landel-Ferry (WLF) theory has been used to correlate the writing process and relaxation relative time constants with the relative temperature, i.e. T-Tg . The validity of this model for the studied materials leads to the assumption that photo-orientation and relaxation processes are mainly dependent on the free volume in the polymer matrix. This hypothesis has been assessed in the case of [11-(N-carbazolyl)undecyl methacrylate]-based materials. [less ▲]

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See detailSynthesis and bulk characterization of new P(CB-b-S) diblock copolymers
Stone, V. W.; Jonas, Alain M; Legras, Roger et al

in Journal of Polymer Science. Part A, Polymer Chemistry (1999), 37(2), 233-244

Strongly asymmetric chlorinated polybutadiene-b-polystyrene, [P((CB)x-b-(PS)y)] diblock copolymers with increasing x/(x + y) ratios (up to 5.2 mol %) have been synthesized by the selective chlorination of ... [more ▼]

Strongly asymmetric chlorinated polybutadiene-b-polystyrene, [P((CB)x-b-(PS)y)] diblock copolymers with increasing x/(x + y) ratios (up to 5.2 mol %) have been synthesized by the selective chlorination of the polybutadiene (PB) block in solution. Chlorination has been performed in anhydrous dichloromethane added with an antioxidant [2,2-methylenebis-(6-tert-butyl-4-methyl-phenol)], at -50°C, under a continuous Ar flow and in the dark. Under the optimized experimental conditions, the PB chlorination is not complete, but the PS block is left unmodified. Even in the presence of a large chlorine excess (Cl2/butene unit molar ratio of 2.5), the experimental degree of chlorination of homo PB does not exceed 85%. The chlorinated copolymers have been characterized by 1H-NMR, IR spectroscopy, size-exclusion chromatography, and elemental analysis. The chlorinated copolymers have also been studied by DSC and SAXS after annealing at 150°C. Although at this temperature the parent homopolymers are immiscible, no microphase separation has been observed for the block copolymers. [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 detailControlled radical polymerization of (meth)acrylates by ATRP with NiBr2(PPh3)2 as catalyst
Moineau, Georges; Minet, Michaël; Dubois, Philippe ULg et al

in Macromolecules (1999), 32(1), 27-35

NiBr2(PPh3)2 has been found to be an efficient catalyst for the ATRP of methyl methacrylate (MMA) and n-butyl acrylate (n-BuA) initiated by an alkyl halide in the absence of any activator (e.g., Lewis ... [more ▼]

NiBr2(PPh3)2 has been found to be an efficient catalyst for the ATRP of methyl methacrylate (MMA) and n-butyl acrylate (n-BuA) initiated by an alkyl halide in the absence of any activator (e.g., Lewis acid) at 85 °C. The molecular weight distribution of the poly(meth)acrylates is narrow (Mw/Mn = 1.1−1.4). However, some side reactions (more likely coupling reactions) are observed at high monomer conversions in the case of n-BuA. An excess of PPh3 has proved to increase the polymerization rate of MMA while preserving the control of the molecular parameters. When the catalyst/initiator molar ratio is too small (e.g., 0.05), the polymerization rate decreases, the polydispersity increases, and the initiation is less efficient. α-Acid and α-hydroxyl end groups have been successfully attached to the chains by using functional initiators, such as 2-bromo-2-methylpropionic acid and 2,2‘,2‘ ‘-tribromoethanol. Reactivity ratios for the MMA/n-BuA comonomer pair have been measured and found to be close to the values observed for a conventional free-radical polymerization. Diethyl meso-2,5-dibromoadipate has been used as a difunctional initiator for the n-BuA polymerization, leading to α,ω-bromo-poly(n-BuA) of narrow molecular weight distribution. Finally, the thermal stability of PMMA is consistent with the lack of termination reactions, while Tg is as high as 125 °C. [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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