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See detailControlled radical polymerization of styrene mediated by the C-phenyl-N-tert-butylnitrone/AIBN pair: Kinetics and electron spin resonance analysis
Sciannamea, Valérie; Catala, Jean-Marie; Jérôme, Robert ULg et al

in Journal of Polymer Science. Part A, Polymer Chemistry (2007), 45(7), 1219-1235

Kinetics of the free radical polymerization of styrene at 110 degrees C has been investigated in the presence of C-phenyl-N-tert-butylnitrone (PBN) and 2,2'-azobis(isobutyronitrile) (AIBN) after ... [more ▼]

Kinetics of the free radical polymerization of styrene at 110 degrees C has been investigated in the presence of C-phenyl-N-tert-butylnitrone (PBN) and 2,2'-azobis(isobutyronitrile) (AIBN) after prereaction in toluene at 85 degrees C. The effect of the prereaction time and the PBN/AIBN molar ratio on the in situ formation of nitroxides and alkoxyamines (at 85 degrees C), and ultimately on the control of the styrene polymerization at 110 degrees C, has been investigated. As a rule, the styrene radical polymerization is controlled, and the mechanism is one of the classical nitroxide-mediated polymerization. Only one type of nitroxide (low-molecular-mass nitroxide) is formed whatever the prereaction conditions at 85 degrees C, and the equilibrium constant (K) between active and dormant species is 8.7 x 10(-10) mol L-1 at 110 degrees C. At this temperature, the dissociation rate constant (k(d)) is 3.7 x 10(-3) s(-1), the recombination rate constant (k(c)) is 4.3 x 10(6) L mol(-1) s(-1), whereas the activation energy (E-a,E-diss), for the dissociation of the alkoxyamine at the chain-end is similar to 125 kJ mol(-1). Importantly, the propagation rate at 110 degrees C, which does not change significantly with the prereaction time and the PBN/AIBN molar ratio at 85 degrees C, is higher than that for the thermal polymerization at 110 degrees C. This propagation rate directly depends on the equilibrium constant K and on the alkoxyamine and nitroxide concentrations, as well. [less ▲]

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See detailControlled radical polymerization of vinyl acetate based on cobalt(II) acetyl acetonate
Debuigne, Antoine ULg; Detrembleur, Christophe ULg; Caille, Jean-Raphaël et al

in Chimie Nouvelle (2005)

Controlled radical polymerization (CRP) is a valuable strategy to design a large range of polymers with well defined molecular characteristics under non very demanding conditions. However, the known CRP ... [more ▼]

Controlled radical polymerization (CRP) is a valuable strategy to design a large range of polymers with well defined molecular characteristics under non very demanding conditions. However, the known CRP techniques, such as nitroxide mediated polymerization (NMP), atom transfer radical polymerization (ATRP) and radical addition-fragmentation chain transfer polymerization (RAFT), suffer from limitations, including a moderate control on the vinyl acetate polymerization. Within the search for new controlled radical polymerization processes, we designed a system based on the reversible combination of growing macroradicals with a cobalt(II)acetylacetonate complex which provides an effective control of the vinyl acetate polymerization even when carried out in suspension in water. In a macromolecular engineering effort, well-defined end-functional poly(vinyl acetate), and poly(vinyl acetate) or poly(vinyl alcohol) containing block copolymers have been synthesized. [less ▲]

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See detailControlled radical polymerization of vinyl monomers catalyzed by ruthenium N-heterocyclic carbene complexes
Demonceau, Albert ULg; Delfosse, Sébastien ULg; Richel, Aurore ULg et al

in Abstracts of Papers - American Chemical Society, National Meeting (2005), 230

As part of our program devoted to the development of new metal-NHC catalyst systems, we have launched a detailed investigation on the catalytic activity of ruthenium-p-cymene complexes bearing NHC ligands ... [more ▼]

As part of our program devoted to the development of new metal-NHC catalyst systems, we have launched a detailed investigation on the catalytic activity of ruthenium-p-cymene complexes bearing NHC ligands for the ring opening metathesis polymerization (ROMP) of cyclic olefins and for the ATRP of vinyl monomers. We report herein on the use for ATRP of [RuCl2(p-cymene)(NHC)] complexes generated in situ by combining the [RuCl2(p-cymene)]2 dimer with an imidazolium salt and a base such as potassium tert-butoxide, cesium carbonate or aluminum isopropoxide. [less ▲]

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See detailControlled radical polymerization of vinyl monomers catalyzed by ruthenium N-heterocyclic carbene complexes
Delfosse, Sébastien; Richel, Aurore ULg; Delaude, Lionel ULg et al

in Matyjaszewski, K. (Ed.) Progress in Controlled/Living Radical Polymerization / ACS Symposium Series 944 (2006)

The relative catalytic activities of a series of ruthenium-based complexes of the general formula [RuCl2(p-cymene)(NHC)], [RuCl2(=CHPh)(PR3)(NHC)] and [RuCl2(=CHPh)(NHC)2] (NHC is a N-heterocyclic carbene ... [more ▼]

The relative catalytic activities of a series of ruthenium-based complexes of the general formula [RuCl2(p-cymene)(NHC)], [RuCl2(=CHPh)(PR3)(NHC)] and [RuCl2(=CHPh)(NHC)2] (NHC is a N-heterocyclic carbene ligand) were determined by investigating the atom transfer radical polymerization (ATRP) of methyl mathacrylate and styrene. The catalytic activity of a variety of related [RuCl(O^N)(=CHR)(NHC)] complexes and their cationic couterparts, [Ru(O^N)(=CHR)(NHC)]+BF4- (R = Ph or OEt, O^N is a Schiff base ligand), is also reported. The results clearly demonstrate that, with both methyl methacrylate and styrene, subtle modifications of the substituents of the NHC ligand lead to dramatic changes in the ability of the resulting ruthenium complexes to favor the occurence of a well-behaved ATRP. [less ▲]

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See detailControlled RAFT synthesis of polyacrylonitrile-b-poly(acrylic acid) diblocks as precursors of carbon nanocapsules with assistance of gold nanoparticles
Aqil, Abdelhafid ULg; Detrembleur, Christophe ULg; Gilbert, Bernard ULg et al

in Chemistry of Materials (2007), 19(9), 2150-2154

A new strategy for the synthesis of carbon nanocapsules has been developed, based on the preparation of well-defined polyacrylonitrile-b-poly(acrylic acid) (PAN-b-PAA) block copolymers followed by their ... [more ▼]

A new strategy for the synthesis of carbon nanocapsules has been developed, based on the preparation of well-defined polyacrylonitrile-b-poly(acrylic acid) (PAN-b-PAA) block copolymers followed by their micellization in basic water to form spherical micelles with a PAN core and PAA shell. The PAN is then cross-linked by the use of gold nanoparticles. After pyrolysis, carbon nanocapsules are produced by graphitization of the PAN core and diffusion of the molten gold nanoparticles out of the nano-objects. [less ▲]

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See detailControlled release of drug from multicomponent device
Nizet, Dominique; Zalfen, Alina; Jérôme, Christine ULg et al

Poster (2007)

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See detailControlled release of drugs from an original multi-component device
Nizet, dominique; Zalfen, Alina; Collard, Laurence ULg et al

Poster (2007)

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See detailControlled release of drugs from multi-component biomaterials
Zalfen, Alina ULg; Nizet, D.; Jérôme, Christine ULg et al

in Acta Biomaterialia (2008), 4(6), 1788-1796

In order to control their release, drugs are encapsulated into systems which are expected to provide a certain site with a predetermined amount of drug over a well-defined period of time. Here we report ... [more ▼]

In order to control their release, drugs are encapsulated into systems which are expected to provide a certain site with a predetermined amount of drug over a well-defined period of time. Here we report on a multi-component drug delivery biomaterial that consists of a hydrogel matrix in which drug-loaded biodegradable microcarriers are dispersed, and whose potential applications could be found in the design of implantable devices with long-term activity, as required by contraceptive and hormone replacement treatments. The release profile of the drug can actually be tuned by the complex interplay of several release mechanisms, including the permeability and eventually the degradation rate of the microcarriers and the diffusion through the hydrogel. The hydrogel consisted of 2-hydroxyethyl methacrylate cross-linked by ethylene glycol dimethacrylate. The microcarriers were biodegradable poly-ε-caprolactone (PCL) microspheres in which active molecules, such as levonorgestrel (LNG), were encapsulated. The hydrogels were characterized by water swelling, thermal properties, LNG diffusion through drug-free and drug-depleted hydrogel membranes and LNG release from devices with drug dispersed in the hydrogel. The PCL microspheres were observed by scanning electron microscopy; their size distribution, LNG loading and release were also investigated. The hydrogel-microsphere assemblies were characterized in terms of the distribution of the microspheres within the hydrogel, water swelling and the release of the encapsulated molecules. The developed device, due to its composite structure, has the ability to combine several release mechanisms, leading to drug release obeying zero-order kinetics for most of the time. [less ▲]

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See detailControlled reproduction of the chub, Leuciscus cephalus (L.) in captivity.
Poncin, Pascal ULg; Melard; Philippart, Jean-Claude ULg

in De Pauw, N.; Jaspers, E.; Ackefors, H. (Eds.) et al Aquaculture - a biotechnology in progress (1989)

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See detailControlled ring-opening polymerization of epsilon-caprolactone in the presence of layered silicates and formation of nanocomposites
Kubies, Dana; Pantoustier, Nadège; Dubois, Philippe et al

in Macromolecules (2002), 35

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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 detailControlled substances and other source gases, Chapter 1 of the Scientific Assessment of Ozone Depletion: 2002
Montzka, S. A.; Fraser, P. J.; Butler, J. H. et al

in Nohende Ajavon, Ayité-Lô; Albritton, Daniel L.; Mégie, Gérard (Eds.) et al Scientific Assessment of Ozone Depletion: 2002 (2003)

This chapter provides an update on scientific progress since the previous Scientific Assessment of Ozone Depletion (WMO, 1999) regarding ozone-depleting substances (ODSs) in the atmosphere. This includes ... [more ▼]

This chapter provides an update on scientific progress since the previous Scientific Assessment of Ozone Depletion (WMO, 1999) regarding ozone-depleting substances (ODSs) in the atmosphere. This includes a discussion of the latest available data for observed trends in the troposphere and stratosphere, emissions, lifetimes, Ozone Depletion Potentials (ODPs), and Global Warming Potentials (GWPs). On the basis of this updated informaion, we relate observations of ODSs in the atmosphere to expectations, and discuss the evidence that the Montreal Protocol is effectively reducing ozone-depleting gases in the atmosphere. [less ▲]

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See detailControlled synthesis and chemical modification of unsaturated aliphatic (co)polyesters based on 6,7-dihydro-2(3H)-oxepinone
Lou, Xudong; Detrembleur, Christophe ULg; Lecomte, Philippe ULg et al

in Journal of Polymer Science. Part A, Polymer Chemistry (2002), 40(14), 2286-2297

A pure unsaturated cyclic ester, 6,7-dihydro-2(3H)-oxepinone (DHO2), was prepared by a new synthetic route. The copolymerization of DHO2 with epsilon-caprolactone (CL) was initiated by aluminum ... [more ▼]

A pure unsaturated cyclic ester, 6,7-dihydro-2(3H)-oxepinone (DHO2), was prepared by a new synthetic route. The copolymerization of DHO2 with epsilon-caprolactone (CL) was initiated by aluminum isopropoxide [Al(OiPr)3] at 0 °C as an easy way to produce unsaturated aliphatic polyesters with nonconjugated CC double bonds in a controlled manner. The chain growth was living, as certified by the agreement between the experimental molecular weight at total monomer conversion and the value predicted from the initial monomer/initiator molar ratio. The polydispersity was reasonably low (weight-average molecular weight/number-average molecular weight 1.2). The homopolymerization of DHO2 was, however, not controlled because of fast intramolecular transesterification. Copolymers of DHO2 and CL were quantitatively oxidized with the formation of epoxides containing chains. The extent of the epoxidation allowed the thermal properties and thermal stability of the copolyesters to be modulated. The epoxidized copolyesters were successfully converted into thioaminated chains, which were then quaternized into polycations. No degradation occurred during the chemical modification. [less ▲]

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See detailControlled synthesis and interface properties of new amphiphilic PCL-g-PEO copolymers
Rieger, Jutta ULg; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Langmuir (2006), 22(18), 7471-7479

Novel biodegradable and biocompatible poly(epsilon-caprolactone)-graft-poly(ethylene oxide), PCL-g-PEO, copolymers consisting of biocompatible blocks have been synthesized by ring-opening copolymerization ... [more ▼]

Novel biodegradable and biocompatible poly(epsilon-caprolactone)-graft-poly(ethylene oxide), PCL-g-PEO, copolymers consisting of biocompatible blocks have been synthesized by ring-opening copolymerization of epsilon-caprolactone (epsilon CL) and a poly(ethylene oxide) (PEO) macromonomer, i.e., PEO end-capped by an epsilon-caprolactone unit (gamma PEO.CL). The control is effective on the composition and length of both the hydrophobic polyester backbone and the hydrophilic PEO grafts. The reactivity ratios have been determined by monitoring the copolymer composition in relation to the comonomer conversion. The PCL-g-PEO copolymers have a tapered (gradient) rather than a random structure consistent with r(epsilon)CL = 3.95 and r(gamma)PEO.CL = 0.05. The amphiphilic graft copolymers display surfactant properties similar to those of PEO-b-PCL diblock copolymers of comparable composition and solubility, as supported by CHCl3/water interfacial tension measured by the pendant drop method. [less ▲]

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See detailControlled Synthesis of AB2 amphiphilic triarm star-shaped block copolymers by ring-opening polymerization
Petrova, Svetla; Riva, Raphaël ULg; Jérôme, Christine ULg et al

in European Polymer Journal (2009), 45(12), 3442-3450

This paper describes the synthesis of a novel amphiphilic AB2 triarm star-shaped copolymer with A = non-toxic and biocompatible hydrophilic poly(ethylene oxide) (PEO) and B = biodegradable and hydrophobic ... [more ▼]

This paper describes the synthesis of a novel amphiphilic AB2 triarm star-shaped copolymer with A = non-toxic and biocompatible hydrophilic poly(ethylene oxide) (PEO) and B = biodegradable and hydrophobic poly(ε-caprolactone) (PCL). A series of AB2 triarm star-shaped copolymers with different molecular weights for the PCL block were successfully synthesized by a three-step procedure. α-methoxy-ω-epoxy-poly(ethylene oxide) (PEO-epoxide) was first synthesized by the nucleophilic substitution of α-methoxy-ω-hydroxy-poly(ethylene oxide) (MPEO) on epichlorohydrin. In a second step, the α-methoxy-ω,ω’-dihydroxy-poly(ethylene oxide) (PEO(OH)2) macroinitiator was prepared by the selective hydrolysis of the ω-epoxy end-group of the PEO-epoxide chain. Finally, PEO(OH)2 was used as a macroinitiator for the ring-opening polymerization (ROP) of ε-caprolactone (εCL) catalyzed by tin octoaote (Sn(Oct)2). PEO-epoxide, PEO(OH)2 and the AB2 triarm star-shaped copolymers were assessed by 1H NMR spectroscopy, size exclusion chromatography (SEC) and MALDI-TOF. The behavior of the AB2 triarm star-shaped copolymer in aqueous solution was studied by dynamic light scattering (DLS) and transmission electron microscopy (TEM). [less ▲]

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See detailControlled synthesis of an ABC miktoarm star-shaped copolymer by sequential ring-opening polymerization of ethylene oxide, benzyl beta-malolactonate, and epsilon-caprolactone
Rieger, Jutta ULg; Coulembier, Olivier; Dubois, Philippe ULg et al

in Macromolecules (2005), 38(26), 10650-10657

This paper reports on the synthesis of an amphiphilic miktoarm ABC star-shaped copolymer, s[(PEO)(PMLABz)(PCL)], consisting of biocompatible/bioresorbable arms. Indeed, PEO is a hydrophilic biocompatible ... [more ▼]

This paper reports on the synthesis of an amphiphilic miktoarm ABC star-shaped copolymer, s[(PEO)(PMLABz)(PCL)], consisting of biocompatible/bioresorbable arms. Indeed, PEO is a hydrophilic biocompatible poly(ethylene oxide) arm, PMLABz is a poly(benzyl beta-malolactonate) arm precursor of a pH-sensitive bioresorbable poly(beta-malic acid) block, and PCL is a hydrophobic bioresorbable poly(epsilon-caprolactone) arm. Each constitutive arm was prepared by ring-opening polymerization. A double-headed PEO macroinitiator [PEO-(OH)-COO-K+] was first prepared by selective hydrolysis of the alpha-lactone (2-oxepanone) end group of PEO chains end-capped by a omega-methoxy group. The anionic polymerization of benzyl beta-malolactonate (MLABz) was selectively initiated by the alpha-potassium carboxylate end group of PEO in the presence of 18-crown-6 ether. The polymerization of epsilon-caprolactone (epsilon-CL) was initiated by the hydroxyl group left at the junction of the two blocks of the as-prepared PEO-b-PMLABz diblock copolymer, in the presence of tin(II) bis(2-ethylhexanoate) (Sn(Oct)(2)). The macroinitiator, the intermediate diblock, and the final miktoarm. star-shaped copolymer were analyzed by H-1 NMR spectroscopy and size exclusion chromatography. [less ▲]

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See detailControlled synthesis of anthracene-labeled omega-amine polystyrene to be used as a probe for interfacial reaction with mutually reactive PMMA
Yin, Zhihui; Koulic, Christian; Pagnoulle, Christophe et al

in Macromolecular Chemistry and Physics (2002), 203(14), 2021-2028

Anthracene-labeled polystyrene (PS) end-capped by a primary amine has been synthesized by atom transfer radical copolymerization of styrene with 3-isopropenyl-alpha,alpha-dimethylbenzyl isocyanate (m-TMI ... [more ▼]

Anthracene-labeled polystyrene (PS) end-capped by a primary amine has been synthesized by atom transfer radical copolymerization of styrene with 3-isopropenyl-alpha,alpha-dimethylbenzyl isocyanate (m-TMI). The m-TMI co-monomer (5.7 mol-%) does not perturb the control of the radical polymerization of styrene. The pendant isocyanate groups of the copolymer chains of low polydispersity (M-w/M-n = 1.25) and controlled molecular weight (up to 35 000) have been derivatized into anthracene by a reaction with 9-methyl(aminomethyl)anthracene. The anthracene-labeled PS (ca. 2 mol-% label) has been conveniently analyzed by size-exclusion chromatography with a UV detector (SEC-UV). Moreover, the omega-bromide end-group of the copolymer chains has been derivatized into a primary amine, making the labeled PS chains reactive towards non-miscible poly(methyl methacrylate) (PMMA) chains end-capped by an anhydride. The interfacial coupling of the mutually reactive PS and PMMA chains has been studied under static conditions (i.e., at the interface between thin PS and PMMA films) and successfully analyzed by SEC-UV. [less ▲]

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