Publications (78)230.43 Total impact
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Article: Dendritic carrier based on PEG: design and degradation of acid-sensitive dendrimer-like poly(ethylene oxide)s.
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ABSTRACT: Degradable dendrimer-like PEOs were designed using an original ABC-type branching agent featuring a cleavable ketal group, following an iterative divergent approach based on the anionic ring opening polymerization (AROP) of ethylene oxide and arborization of PEO chain ends. A seventh generation dendrimer-like PEO carrying 192 peripheral hydroxyls and exhibiting a molar mass of 446 kg · mol(-1) was obtained in this way. The chemical degradation of these dendritic scaffolds was next successfully accomplished under acidic conditions, forming linear PEO chains of low molar mass (≈2 kg · mol(-1)), as monitored by (1)H NMR, SEC, and MALDI-TOF mass spectrometry as well as by AFM.Macromolecular Rapid Communications 11/2011; 32(21):1722-8. · 4.60 Impact Factor -
Chapter: Recent Trends in Macromolecular Engineering Using Ring‐Opening Metathesis Polymerization
09/2011: pages 249 - 293; , ISBN: 9783527631421 -
Chapter: Anionic Polymerization of Vinyl and Related Monomers
09/2011: pages 7 - 55; , ISBN: 9783527631421 -
Article: Sequential functionalization of janus‐type dendrimer‐like poly(ethylene oxide)s with camptothecin and folic acid
Journal of Polymer Science Part A Polymer Chemistry 05/2011; 49(13):2839 - 2849. · 3.92 Impact Factor -
Article: Expanding the Scope of Group Transfer Polymerization Using N-Heterocyclic Carbenes as Catalysts: Application to Miscellaneous (Meth)acrylic Monomers and Kinetic Investigations
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ABSTRACT: 1,3-Bis(di-isopropyl)imidazol-2-ylidene (1) and 1,3-bis(di-tert-butyl)imidazol-2-ylidene (2), which are N-heterocyclic carbenes (NHCs) are shown to catalyze the solution group transfer polymerization (GTP) of miscellaneous monomers in a controlled fashion at room temperature, in the presence of 1-methoxy-2-methyl-1-trimethylsiloxypropene (MTS) as initiator. The ability of seven distinct monomers, methyl methacrylate (MMA), tert-butyl acrylate (tBA), n-butyl acrylate (nBA), N,N-dimethylaminoethyl acrylate (DMAEA), N,N-dimethyl acrylamide (DMA), N,N-dimethylaminoethyl methacrylate (DMAEMA), and methacrylonitrile (MAN) to polymerize via GTP by NHC catalysis has been evaluated. The first-order kinetic plots, that is the evolution of ln[M]0/[M] versus time, systematically deviate from linearity, with the noticeable exception of GTP of DMA. A direct dependence of the rate of GTP on the concentration in MTS initiator is observed in the case of tBA carried out in THF, that is, the rate of polymerization increases with [MTS], with a first-order dependence on [MTS]. These results suggest the formation of hypervalent siliconate intermediates in NHC-induced GTP of acrylic monomers which proceeds via an associative mechanism. The nonlinear variation of ln[M]0/[M] with time in the terminal phase of the polymerization of both acrylates and methacrylates may be explained by the development of strong interactions between the NHC and pendant ester groups of poly(meth)acrylates, limiting the availability of the catalyst for chain end activation. In contrast, interactions between the NHC and amide-type units of poly(DMA) are unlikely, NHCs being not known as effective catalysts for transamidation reactions. A first-order kinetic plot with a linear variation of ln[M]0/[M] with time is thus observed for the NHC-catalyzed GTP of DMA.10/2010; -
Article: Metal-free and solvent-free access to alpha,omega-heterodifunctionalized poly(propylene oxide)s by N-heterocyclic carbene-induced ring opening polymerization.
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ABSTRACT: A N-heterocyclic carbene, namely, 1,3-bis-(diisopropyl)imidazol-2-ylidene either directly initiates or catalyzes the metal-free ring opening polymerization of neat propylene oxide at 50 degrees C, affording well-defined alpha,omega-heterodifunctionalized poly(propylene oxide) oligomers.Chemical Communications 05/2010; 46(18):3203-5. · 6.17 Impact Factor -
Article: N-Heterocyclic Carbene-Organocatalyzed Ring-Opening Polymerization of Ethylene Oxide in the Presence of Alcohols or Trimethylsilyl Nucleophiles as Chain Moderators for the Synthesis of α,ω-Heterodifunctionalized Poly(ethylene oxide)s
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ABSTRACT: The present study describes innovations in the ring-opening polymerization (ROP) of ethylene oxide (EO) using N-heterocyclic carbenes (NHCs) as organocatalysts, which enables the synthesis of α,ω-heterodifunctionalized poly(ethylene oxide)s (PEOs). Two representative NHC catalysts, namely, 1,3-bis(diisopropyl)imidazol-2-ylidene (1) and 1,3-bis(di-tert-butyl)imidazol-2-ylidene (2), were efficiently employed in conjunction with a variety of chain regulators of general structure NuE, where Nu and E are the nucleophilic and the electrophilic part, respectively, with E = H or SiMe3 (e.g., PhCH2OH, HC≡CCH2OH, N3SiMe3, and PhCH2OSiMe3). Catalytic amounts of the NHC (typically [NHC]/[NuE]/[EO] = 0.1/1/100 in moles) were indeed utilized to trigger the metal-free ROP of EO at 50 °C in dimethyl sulfoxide, allowing the polymerization to proceed to completion. In this way, PEOs of dispersities lower than 1.2 and molar masses perfectly matching the [EO]/[NuE] ratio were obtained, attesting to the controlled/living character of these NHC-catalyzed polymerizations. Characterization of α,ω-difunctionalized PEOs by combined techniques such as 1H NMR spectroscopy, MALDI-TOF mass spectrometry, and size exclusion chromatography confirmed the quantitative introduction of the nucleophilic moiety (Nu) and its electrophilic component (E = H or SiMe3) in the α- and ω-position of the PEO chains, respectively, and the formation of polymers with narrowly distributed molar masses. These results are discussed in the light of the existence of two possible mechanisms. The first one involves a direct attack of the NHC catalyst onto EO and the formation of a zwitterionic intermediate (activated monomer mechanism). The second possibility is the activation by the NHC of the E moiety of the NuE chain regulator first and then of the α-Nu,ω-OE PEO chain (activated chain end mechanism).02/2010; -
Article: Fast Access to Dendrimer-like Poly(ethylene oxide)s through Anionic Ring-Opening Polymerization of Ethylene Oxide and Use of Nonprotected Glycidol as Branching Agent
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ABSTRACT: Dendrimer-like poly(ethylene oxide)s (PEOs) were synthesized through a semicontinuous process based on the anionic ring-opening polymerization (AROP) of ethylene oxide (EO), followed by AROP of a mixture of glycidol (G) and propylene oxide (PO). Glycidol was used as branching agent generating two hydroxyl groups after ring-opening, whereas propylene oxide served to prevent the aggregation of the generated terminal alkoxides. A three-armed PEO star was first prepared through AROP of EO from 1,1,1-tris(hydroxymethyl)ethane as trifunctional precursor using dimethyl sulfoxide (DMSO) as solvent. After completion of EO polymerization and without isolating the PEO star precursor, G and PO (molar ratio 1:3) were added in the same batch to be polymerized either sequentially or randomly. This led to a three-armed PEO star with an average number of terminal hydroxyls per arm which depended on the number of G units inserted at PEO chain ends, as determined by 1H NMR spectroscopy. Growth of the second and the third generation of PEO could be achieved upon reiterating the same steps of AROP of EO and subsequent AROP of G and PO (arborization step) in one pot, affording dendrimer-like PEOs of generation 3 with moderately distributed but expected molar masses. In a variant of this strategy, G was copolymerized in the presence of allyl glycidyl ether during the arborization step in order to introduce allylic double bonds at the branching points of the dendrimer-like PEOs.10/2009; -
Article: Group Transfer Polymerization of (Meth)acrylic Monomers Catalyzed by N-Heterocyclic Carbenes and Synthesis of All Acrylic Block Copolymers: Evidence for an Associative Mechanism
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ABSTRACT: N-Heterocyclic carbenes (NHCs), namely, 1,3-bis-(diisopropyl)imidazol-2-ylidene (1) and 1,3-bis(di-tert-butyl)imidazol-2-ylidene (2) were employed as neutral organocatalysts to bring about the group transfer polymerization (GTP) of both methacrylic and acrylic monomers, including methyl methacrylate (MMA), tert-butylacrylate (tBA), and n-butylacrylate (nBA). This could be achieved at room temperature using 1-methoxy-2-methyl-1-trimethylsiloxypropene (MTS) as initiator in polar or apolar medium. In this way, polymethacrylates and polyacrylates with molar masses in the range 10 000−300 000 g·mol−1, corresponding to the initial [monomer]/[MTS] ratio and with polydispersities lower than 1.2, were obtained in quantitative yields. The kinetics of GTP of MMA catalyzed by 1 or 2 was further investigated. Though the first-order kinetic plot ln[M]0/[M] versus time deviated from linearity at high monomer conversion, no inhibition period was noted at low monomer conversion. Moreover, the polymerization rate dramatically increased as the concentration of initiator increased, with first-order dependence in initiator. When mixed in 1/1 molar ratio, MTS and NHC 1 did not reveal the formation of enolate-type species by 29Si or 13C NMR spectroscopy. Based on these observations, we propose that NHCs activate the silyl ketene acetal initiator and further propagate GTP via an associative mechanism. The fact that ln[M]0/[M] does not evolve linearly with time in the terminal phase of the polymerization can be understood by a reduced diffusion of the catalyst to the trimethylsilyl end groups. The proposed associative mechanism can also account for the successful control of NHC-catalyzed GTP of acrylates during which termination reactions such as backbiting or internal isomerization could be drastically minimized. Next, was described the synthesis of all acrylic block copolymers based on polyacrylates and polymethacrylates (e.g., PMMA-b-PnBA-b-PMMA), utilizing the same NHC as catalyst in sequential GTP. It is again argued that such block copolymer formation is favored by an associative mechanism forming highly unstable activated silicon intermediates.08/2009; -
Article: Step-Growth Polymerization of Terephthaldehyde Catalyzed by N-Heterocyclic Carbenes
07/2009; -
Article: Electronic and steric ligand effects in the radical polymerization of vinyl acetate mediated by beta-ketoiminate complexes of cobalt(II).
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ABSTRACT: Complexes Co[OC(Ph)CHC(Me)NAr](2) [Ar=Ph, 1; o,o'-C(6)H(3)Me(2) (Xyl), 2; p-C(6)H(4)CF(3), 3] are tested in the polymerization of vinyl acetate (VAc) initiated by V-70 (0.8 equiv) at 30 degrees C. Polymerization occurs without any notable induction time yielding PVAc with relatively low polydispersity, but with higher than expected M(n) values, which indicates inefficient trapping processes. The apparent polymerization rate constant varies in the order 2>1>3. Controlled polymer growth is also observed when the polymerization is conducted in the presence of a much higher V-70/1 ratio, demonstrating that this system can also function as a transfer agent in a degenerative transfer process. Competition between chain growth and catalyzed chain transfer (CCT) is also observed, the latter prevailing at higher temperatures. Comparison of these results with previous reports on bis(beta-diketonato) complexes allows a separate assessment of ligand electronic and steric effects in the ability to control polymerization.Chemistry - An Asian Journal 06/2009; 4(8):1257-65. · 4.50 Impact Factor -
Article: Radical polymerization of vinyl acetate with bis(tetramethylheptadionato)cobalt(II): coexistence of three different mechanisms.
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ABSTRACT: The complex [Co(II)(tmhd)(2)] (4; tmhd = 2,2,6,6-tetramethylhepta-3,5-dionato) has been investigated as a mediator for controlled radical polymerization of vinyl acetate (VAc) and compared with the analogue [Co(II)(acac)(2)] (1; acac = acetylacetonato). A relatively well controlled process occurs, after an induction time, with 2,2'-azobis(4-methoxyl-2,4-dimethylvaleronitrile) (V-70) as radical initiator at 30 degrees C. However, whereas the polymerization essentially stops after about six initiator half-lives in the presence of 1, it continues with a first-order rate law in the presence of 4. The successful simulation of the kinetic data shows that 4 operates simultaneously by associative (degenerative transfer, DT) and dissociative (organometallic radical polymerization, OMRP) mechanisms. The occurrence of OMRP was confirmed by an independent polymerization experiment starting from an isolated and purified [Co(tmhd)(2)](PVAc) macroinitiator. The polymer molecular weight evolves linearly with conversion in accordance with the expected values for one chain per Co atom when DT is the predominant mechanism and also during the pure OMRP process; however, observation of stagnating molecular weights at long reaction times with concomitant breakdown of the first-order rate law for monomer consumption indicates a competitive chain-transfer process catalyzed by an increasing amount of Co(II). In the presence of external donors L (water, pyridine, triethylamine) the DT pathway is blocked and the OMRP pathway is accelerated, and polymerization with complex 4 is then about five times slower than with complex 1. The reversal of relative effective OMRP rate constants k(eff) (4>1 in the absence of external donors, 4<1 in their presence) is rationalized through competitive steric effects on Co(III)-C and Co(II)-L bond strengths. These propositions are supported by (1)H NMR studies and by DFT calculations.Chemistry 04/2009; 15(19):4874-85. · 5.93 Impact Factor -
Article: N-heterocyclic carbene-induced zwitterionic ring-opening polymerization of ethylene oxide and direct synthesis of alpha,omega-difunctionalized poly(ethylene oxide)s and poly(ethylene oxide)-b-poly(epsilon-caprolactone) block copolymers.
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ABSTRACT: An N-heterocyclic carbene (NHC), namely, 1,3-bis-(diisopropyl)imidazol-2-ylidene (1), was demonstrated to bring about the metal-free ring-opening polymerization of ethylene oxide at 50 degrees C in dimethyl sulfoxide, in absence of any other reagents. Poly(ethylene oxide) (PEO) of polydispersities <1.2 and molar masses perfectly matching the [monomer]/[(1)] ratio could thus be obtained in quantitative yields, attesting to the controlled/living character of such carbene-initiated polymerizations. It is argued that (1) adds to ethylene oxide to form a zwitterionic species, namely 1,3-bis-(diisopropyl)imidazol-2-ylidinium alkoxide, that further propagates by a zwitterionic ring-opening polymerization (ZROP) mechanism. Through an appropriate choice of terminating agent NuH or NuSiMe(3) at the completion of the polymerization, a variety of end-functionalized PEO chains could be generated. In particular, alpha,omega-bis(hydroxy)-telechelic PEO, alpha-benzyl,omega-hydroxy, and alpha-azido,omega-hydroxy-difunctionalized PEOs were synthesized by NHC (1)-initiated ZROP, using H(2)O, PhCH(2)OH, and N(3)SiMe(3) as terminating agent, respectively. Characterization of these alpha,omega-difunctionalized PEOs by techniques such as (1)H NMR spectroscopy, MALDI-TOF spectrometry, and size exclusion chromatography confirmed the quantitative introduction of functional groups at both alpha and omega positions of the PEO chains and the formation of very narrow molar mass polymers. Finally, the synthesis of a poly(ethylene oxide)-b-poly(epsilon-caprolactone) diblock copolymer by sequential ZROP of the corresponding monomers was successfully achieved using (1) as organic initiator without isolation of the PEO block intermediate.Journal of the American Chemical Society 02/2009; 131(9):3201-9. · 9.91 Impact Factor -
Article: Micelles and polymersomes obtained by self-assembly of dextran and polystyrene based block copolymers.
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ABSTRACT: The self-assembly of dextran-block-polystyrene (dex-b-PS) block copolymers was investigated in solution. The hydrophobic PS weight fraction in these block copolymers ranges from 7 to 92% w/w, whereas the average number molar mass of dextran was kept constant at 6600 gmol(-1). Self-assembly by direct dissolution in water could be performed only for block copolymers with a low hydrophobic content (7% w/w), whereas mixtures of tetrahydrofuran and dimethylsulfoxide were required for higher PS content, before transferring the structures into water. Core-shell micelles, ovoïds, and vesicles could be identified upon characterization by light and neutrons scattering, atomic force microscopy, and transmission electron microscopy. Most of the morphologies observed were not expected considering the chemical composition of the block copolymers. Finally, the size and shape of these nanoparticles were fixed upon cross-linking the dextran block through reaction of the hydroxyl groups with divinylsulfone. The role of the dextran conformation on the self-assembly process is discussed.Biomacromolecules 01/2009; 10(1):32-40. · 5.48 Impact Factor -
Article: Janus-type dendrimer-like poly(ethylene oxide)s.
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ABSTRACT: A straightforward and original methodology allowing the synthesis of Janus-type dendrimer-like poly(ethylene oxide)s (PEOs) carrying orthogonal functional groups on their surface is described. The use of 3-allyloxy-1,2-propanediol (1) as a latent AB2-type heterofunctional initiator of anionic ring-opening polymerization (AROP) of ethylene oxide (EO) and of selective branching agents of PEO chain ends served to construct the two dendrons of these dendrimer-like PEOs, following a divergent pathway. Thus, the first PEO generation of the first dendron was grown by AROP from 1 followed by the reaction of the corresponding alpha-allyl,omega,omega'-bishydroxy- heterofunctional PEO derivative with 2-(3'-chloromethybenzyloxymethyl)-2-methyl-5,5-dimethyl-1,3-dioxane (2) used as a branching agent. This afforded the dendron A with four latent peripheral hydroxyls protected in the form of two ketal rings. The remaining alpha-allylic double bond of the PEO thus prepared was transformed into two hydroxyl groups using OsO4 in order to create the first PEO generation of the dendron B by AROP of EO. Allyl chloride (3) was then used as another (latent) branching agent to react with the terminal hydroxyl of the corresponding PEO chains. Deprotection under acidic conditions of the ketal groups of dendron A, followed by AROP of EO, afforded the second PEO generation on this face. This alternate and divergent procedure, combining AROP of EO and selective branching of PEO branches, could be readily iterated, one dendron after the other up to the generation six, leading to a Janus-type dendrimer-like PEO exhibiting a total mass of around 300 kg/mol and possessing 64 peripheral groups on each face. The possibility of orthogonal functionalization of the surfaces of such Janus-type dendritic PEOs was exploited. Indeed, a dendron of generation 4 was functionalized with hydroxyl functions at its periphery, whereas the other was end-capped with either tertiary amino or disulfide groups. In a variant of this strategy, azido groups and acetylene could also be orthogonally introduced at the periphery of the fourth generation Janus-type dendrimer-like PEO and subjected to polycondensation by a 1,3-dipolar cycloaddition reaction. This afforded a necklace-like covalent assembly of dendrimer-like PEOs through the formation of stable [1,2,3]-triazole linkages.Journal of the American Chemical Society 10/2008; 130(35):11662-76. · 9.91 Impact Factor -
Chapter: Guidelines for Synthesizing Block Copolymers
02/2008: pages 9 - 38; , ISBN: 9783527610570 -
Article: Harnessing the potential of N-heterocyclic carbenes for the rejuvenation of group-transfer polymerization of (meth)acrylics.
Angewandte Chemie International Edition 02/2008; 47(29):5390-3. · 13.45 Impact Factor -
Article: Combination of an anionic terminator multifunctional initiator and divergent carbanionic polymerization: application to the synthesis of dendrimer-like polymers and of asymmetric and miktoarm stars.
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ABSTRACT: A new and versatile synthetic strategy that provides access to precisely defined and totally soluble multicarbanionic initiators has been implemented to obtain by divergent growth dendrimer-like samples of polystyrene (PS) (up to the seventh generation) or polybutadiene (PB) (up to the third generation) and also asymmetric and miktoarm stars. This strategy rests on lithium-halide exchange reactions to generate multicarbanionic species and on the design of an original reagent that can concomitantly react with living carbanionic chains/arms to deactivate them and produce multicarbanionic sites after exchange of its bromides against lithium. This reagent, 4,4'-dibromodiphenylethylene (1), functions as a TERminating agent and a Multifunctional INItiator (TERMINI), according to a concept first proposed by Percec in another context. Upon using this anionic TERMINI in living carbanionic polymerization and repeating the two steps of chain end derivatization by 1 and divergent arm growth from the multifunctional sites generated, perfectly defined dendrimer-like polystyrene and polybutadiene could be obtained up to the seventh generation for the former and up to the third generation for the latter. Each step, i.e., chain end modification and arm growth, was carefully monitored, and the dendrimer-like samples of PS and PB were all characterized by size exclusion chromatography equipped with a multiangle laser light scattering detector (SEC/LS) and high-temperature size exclusion chromatography equipped with a viscometric detector (HT-SEC). The viscosity behavior of these dendrimer-like polystyrenes--bell-shaped variation versus the number of generation--was found to be similar to that reported for regular dendrimers. This chemistry, namely this anionic TERMINI, was also exploited to derive three-arm asymmetric and miktoarm stars.Journal of the American Chemical Society 02/2008; 130(4):1350-61. · 9.91 Impact Factor -
Article: Synthesis of ATRP-induced dextran-b-polystyrene diblock copolymers and preliminary investigation of their self-assembly in water.
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ABSTRACT: Dextran-b-polystyrene diblock copolymers forming miscellaneous spherical self-assemblies in water were obtained by chemical modification of the anomeric extremity of a commercial dextran followed by atom transfer radical polymerisation of styrene.Chemical Communications 09/2007; · 6.17 Impact Factor -
Article: Bouquet-type dendrimerlike poly(ethylene oxide)s with a focal aldehyde and peripheral hydroxyls.
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ABSTRACT: Doubly functionalized dendrimerlike poly(ethylene oxide)s (PEOs) carrying 16 hydroxyl groups at their periphery and one aldehyde group at their focal point were synthesized up to the fourth generation through an iterative divergent approach. First, a protected aldehyde dihydroxyl compound, namely, 3,3-diethoxy-1,2-propanediol, was used as initiator for the anionic ring-opening polymerization (AROP) of ethylene oxide after partial deprotonation (30%) in dimethyl sulfoxide. The two hydroxyls carried by the PEO chain ends of the first generation were subsequently derivatized so as to generate four hydroxyls via a two-step reaction (allylation and osmylation). The next generations of such dendrimerlike PEOs were grown upon repeating the same cycle of AROP and chain-end modification. At the completion of these reactions, the acetal group present at the core was deprotected under acidic conditions to afford the targeted dendrimerlike PEO of fourth generation with a central aldehyde group. The reactivity and accessibility of the latter function was demonstrated upon its conjugation with aniline used as a model compound.Biomacromolecules 09/2007; 8(8):2374-8. · 5.48 Impact Factor
Top co-authors
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Institutions
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2005–2011
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French National Centre for Scientific Research
Lyon, Rhone-Alpes, France
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1998–2008
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Université Bordeaux 1
- UMR LCPO - Laboratoire de Chimie des Polymères Organiques
Talence, Aquitaine, France
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2005–2007
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University of Florida
- Department of Chemistry
Gainesville, FL, USA
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