6 research outputs found
Pourquoi les paradoxes de ZĂ©non ne remettent pas en question le mouvement mais plutĂŽt lâimmobilitĂ©
Ce document contient la version en français de lâarticle original intitulĂ© « Why Zeno's paradoxes of motion are actually about immobility » publiĂ© dans la revue Foundations of Science (cf. https://hal.archives-ouvertes.fr/hal-02263487 )Les paradoxes du mouvement de ZĂ©non prĂ©tendent nier lâexistence du mouvement. En effet, ils ont Ă©tĂ© conçus dans le seul but de consolider la vision ParmĂ©nidĂ©enne dâun monde immuable et sans changement. Lâobjectif principal de cet article est de dĂ©montrer que ces cĂ©lĂšbres paradoxes logiques devraient plutĂŽt ĂȘtre vus comme des paradoxes de lâimmobilitĂ©. Avec cette nouvelle vision, la notion de mouvement nâest plus problĂ©matique tandis que celle de lâimmobilitĂ© le devient. Ceci est tout sauf embĂȘtant puisque quâil est facile de concevoir le fait que de lâimmobilitĂ© apparente puisse dissimuler du mouvement rĂ©el, et ainsi la proposition « lâimmobilitĂ© nâest quâune illusion de nos sens » semble bien plus crĂ©dible que la thĂšse inverse soutenue par ParmĂ©nide. De plus, cette proposition est Ă©galement en conformitĂ© avec la description moderne des objets matĂ©riels : dans le cadre de la thĂ©orie atomique contemporaine, lâexistence dâun mouvement alĂ©atoire et incessant des atomes â nommĂ© lâagitation thermique â peut offrir une explication rationnelle pour cette âillusion dâimmobilitĂ©â. Cette nouvelle approche des paradoxes de ZĂ©non nous amĂšne aussi Ă introduire le nouveau concept dâimpermobilitĂ©, dont le principal avantage est dâĂȘtre bien plus appropriĂ© (que le concept dâimmobilitĂ©) pour une description sans a priori de la rĂ©alitĂ© des phĂ©nomĂšnes physiques
SynthĂšse dâagents de contrĂŽle originaux pour lâobtention de copolymĂšres α-fonctionnels par le procĂ©dĂ© RAFT. Application Ă lâĂ©laboration de particules Ă chevelure contrĂŽlĂ©e.
alpha-functionalized polymer of controlled chain length can be designed by the use of the RAFT (Reversible Addition Fragmentation chain Transfer) process, which is a controlled radical polymerization technique. The first requirement for this strategy is to synthesize functionalized chain transfer agents (CTA).In this research work, a simple strategy is presented: original dithioester precursors CTA were designed and used to provide a large variety of functionalized dithioesters. The efficiency of this strategy was previously checked with a model compound, and was then applied to the synthesis of dithioesters bearing biomolecules (bio-CTA) like a biotin, a phospholipid or a carbohydrate derivative. RAFT polymerization of N-acryloylmorpholine mediated by each of these new bio-CTAs is well controlled, the resulting polymer exhibiting narrow molar mass distributions (PDI<1.1). Moreover, 1H NMR and MALDI-ToF mass spectrometry analyses confirmed the presence of the biological compound at the alpha-end of the chains.Finally, the same strategy (leading to alpha-bio-functionalized polymers) was used to elaborate macromolecular structures for applications in biological diagnostic tests: 1- a high molecular weight reactive random copolymer was synthesized from the biotin-dithioester, and may serve as âhighly-fluorescentâ detection probes; 2- Functionalized particles with controlled hair were obtained via dispersion polymerization using alpha-functionalized polymer chains bearing a carbohydrate derivative (potentially able to capture pathogenic agents) as precursor stabilizer.Le procĂ©dĂ© RAFT (transfert de chaĂźne par addition-fragmentation rĂ©versible) est une technique de polymĂ©risation radicalaire contrĂŽlĂ©e de choix permettant dâobtenir directement des chaĂźnes polymĂšres alpha-fonctionnelles de longueur contrĂŽlĂ©e. La synthĂšse prĂ©alable dâagents de contrĂŽle (ou agents RAFT) fonctionnalisĂ©s est une Ă©tape primordiale Ă cette stratĂ©gie.Dans ce travail de thĂšse, une stratĂ©gie simple a Ă©tĂ© dĂ©veloppĂ©e pour la synthĂšse dâagents de transfert de chaĂźne fonctionnalisĂ©s : des agents RAFT prĂ©curseurs originaux appartenant Ă la famille des dithioesters ont Ă©tĂ© conçus afin de pouvoir synthĂ©tiser aisĂ©ment une large gamme dâagents RAFT fonctionnalisĂ©s. Cette nouvelle voie de synthĂšse a prĂ©alablement Ă©tĂ© validĂ©e Ă lâaide dâun composĂ© modĂšle avant dâĂȘtre appliquĂ©e Ă la synthĂšse de dithioesters portant un ligand biologique tel que la biotine, un lipide ou un dĂ©rivĂ© carbohydrate.La polymĂ©risation de type RAFT de la N-acryloylmorpholine en prĂ©sence de chacun de ces nouveaux bio-agents RAFT vĂ©rifie tous les critĂšres dâune polymĂ©risation contrĂŽlĂ©e. En particulier, les polymĂšres obtenus ont une distribution des masses molaires trĂšs Ă©troite (Ip<1,1). De plus, la prĂ©sence du ligand biologique en extrĂ©mitĂ© alpha des chaĂźnes a Ă©tĂ© confirmĂ©e par RMN 1H et par spectromĂ©trie de masse MALDI-ToF.Enfin, cette stratĂ©gie de synthĂšse de polymĂšres alpha-bio-fonctionnels a Ă©tĂ© utilisĂ©e pour la conception de structures macromolĂ©culaires rĂ©pondant aux critĂšres requis pour des applications dans le diagnostic biologique : 1) un copolymĂšre rĂ©actif de masses molaires Ă©levĂ©es prĂ©curseur de sondes de dĂ©tection « super-fluorescentes » a Ă©tĂ© synthĂ©tisĂ© Ă partir du dithioester-biotine ; 2) lâutilisation des polymĂšres alpha-fonctionnels synthĂ©tisĂ©s Ă partir du dithioester-sucre a permis lâĂ©laboration de particules fonctionnalisĂ©es Ă chevelure contrĂŽlĂ©e potentiellement utilisables pour la capture dâagents pathogĂšnes. Pour cela, un procĂ©dĂ© de polymĂ©risation mixte associant le principe de la polymĂ©risation en dispersion avec celui de la polymĂ©risation de type RAFT a Ă©tĂ© imaginĂ©
Additional Retardation in RAFT Polymerization: Detection of Terminated Intermediate Radicals
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Sub-micrometer sized hairy latex particles synthesized by dispersion polymerization using hydrophilic macromolecular RAFT agents
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Synthesis of stimuli-responsive double hydrophilic block copolymers by ATRP and RAFT and their use as nanostructure-directing agents of mesoporous silica materials
International audienceA series of double hydrophilic block copolymers DHBCs has been synthesized by controlled radical polymerization (Figure 1). Poly(ethylene oxide)-b-poly(acrylic acid) PEO-b-PAA was prepared by ATRP in acetone. PEO-b-PAA and PEO-b-Poly(N-isopropyl acrylamide) PEO-b-PNIPAM were prepared by RAFT using a PEO-based dithiobenzoate macro-RAFT agent, in water and dioxane respectively. Poly(poly(ethylene glycol) methyl ether acrylate)-b-PAA PmPEGA-b-PAA was prepared by RAFT in water using a trithiocarbonate RAFT agent. Poly(acrylamide)-b-PAA PAM-b-PAA and PAM-b-poly(3-acrylamidopropyl)trimethylammonium chloride) PAM-b-PAPTAC were prepared by RAFT/MADIX using xanthate as control agent, in water/ethanol for the PAM block and directly in water for the second block. The block copolymers have been characterized by SEC, pH titration, conductimetry, and capillary electrophoresis (CE).The reversible formation of micelles by variation of temperature in the case of PEO-b-PNIPAM, or by the mixing of polyelectrolyte DHBCs with a polyelectrolyte of opposite charge in the right range of pH (e.g. anionic PEO-b-PAA associated with cationic oligochitosan) has been studied. The micelles have been characterized by various scattering techniques and CE.Such stimuli-responsive (T, pH, ionic strength) micellar systems have been involved as structuring agents in the synthesis of nanostructured mesoporous silica by sol-gel process. A relationship between the composition of the DHBCs, the composition of the micelles, the experimental conditions of micelle formation and the final mesostructure of the silica materials is foreseen. This strategy has been applied to the preparation of drug-loaded silica for biomedical applications
Synthesis of stimuli-responsive double hydrophilic block copolymers by ATRP and RAFT and their use as nanostructure-directing agents of mesoporous silica materials
International audienceA series of double hydrophilic block copolymers DHBCs has been synthesized by controlled radical polymerization (Figure 1). Poly(ethylene oxide)-b-poly(acrylic acid) PEO-b-PAA was prepared by ATRP in acetone. PEO-b-PAA and PEO-b-Poly(N-isopropyl acrylamide) PEO-b-PNIPAM were prepared by RAFT using a PEO-based dithiobenzoate macro-RAFT agent, in water and dioxane respectively. Poly(poly(ethylene glycol) methyl ether acrylate)-b-PAA PmPEGA-b-PAA was prepared by RAFT in water using a trithiocarbonate RAFT agent. Poly(acrylamide)-b-PAA PAM-b-PAA and PAM-b-poly(3-acrylamidopropyl)trimethylammonium chloride) PAM-b-PAPTAC were prepared by RAFT/MADIX using xanthate as control agent, in water/ethanol for the PAM block and directly in water for the second block. The block copolymers have been characterized by SEC, pH titration, conductimetry, and capillary electrophoresis (CE).The reversible formation of micelles by variation of temperature in the case of PEO-b-PNIPAM, or by the mixing of polyelectrolyte DHBCs with a polyelectrolyte of opposite charge in the right range of pH (e.g. anionic PEO-b-PAA associated with cationic oligochitosan) has been studied. The micelles have been characterized by various scattering techniques and CE.Such stimuli-responsive (T, pH, ionic strength) micellar systems have been involved as structuring agents in the synthesis of nanostructured mesoporous silica by sol-gel process. A relationship between the composition of the DHBCs, the composition of the micelles, the experimental conditions of micelle formation and the final mesostructure of the silica materials is foreseen. This strategy has been applied to the preparation of drug-loaded silica for biomedical applications