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Statistical copolymers of l-lactide (L-LA) and e-caprolactone (CL) are of major interest as a result of the desired combination of properties they exhibit for high-added-value applications, includi...

Despite significant advances in organocatalysis, stereoselective polymerization reactions utilizing chiral organocatalysts have received very little attention, and much about the underlying mechanisms remains unknown. Here, we report that both commercially available (R,R)- and (S,S)-enantiomers of chiral thiourea-amine Takemoto’s organocatalysts promote efficient control and high isoselectivity at room temperature of the ring-opening polymerization (ROP) of racemic lactide by kinetic resolution, yielding highly isotactic, semicrystalline and metal-free polylactide (PLA). Kinetic investigations and combined analyses of the resulting PLAs have allowed the stereocontrol mechanism, which eventually involves both enantiomorphic site control and chain-end control, to be determined. Moreover, epimerization of rac-LA to meso-LA is identified as being responsible for the introduction of some stereoerrors during the ROP process.

International audience; Partially biobased poly(1,2,3-triazolium)s are synthesized by reversible additionfragmentation chain transfer (RAFT) polymerization of tailor-made 1,2,3-triazole-functionalized (meth)acrylate monomers derived from levulinic acid, followed by N-alkylation of the 1,2,3-triazole moieties by methyl iodide (CH3I) and subsequent anion exchange with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). Chain extension of a 1,2,3-triazole-functionalized polymethacrylate by RAFT polymerization of styrene followed by N-alkylation with CH3I and anion exchange with LiTFSI affords two poly(1,2,3-triazole)- and two poly(1,2,3-triazolium)-based diblock copolymers (BCPs) with different weight fractions of each block. Discussion of the structure/properties relationships of all obtained materials is based on NMR spectroscopy, size exclusion chromatography, differential scanning calorimetry, thermogravimetric analysis, and broadband dielectric spectroscopy. The morphological and self-assembling properties of neutral and charged BCPs in bulk and in thin films are investigated by small-angle X-ray scattering and atomic force microscopy experiments, respectively.

Living anionic polymerization gives access to well-defined polymers, but it demands strict purification of reagents and solvents. This work presents the azaanionic polymerization (AAROP) of aziridines as a robust living polymerization technique, with the ease of controlled radical polymerizations. AAROP does not require inert atmosphere and remains living in the presence of large amounts of water or alcohols. Mesyl-, tosyl-, or brosyl-activated aziridines were polymerized with up to 100-fold excess of a protic impurity with respect to the initiator and still being active for chain extension. This allowed the preparation of polyols by anionic polymerization without protective groups, as only minor initiation occurred from the alcohols. The tolerance toward protic additives lies in the electron-withdrawing effect of the activating groups, decreasing the basicity of the propagating species, while maintaining a strong nucleophilic character. In this way, competing alcohols and water are only slightly involved...

International audience; The organometallic-mediated radical polymerization (OMRP) of N-vinyl-3-alkylimidazolium-type monomers, featuring the bis(trifluoromethylsulfonyl)imide counter-anion (Tf2N-) in the presence of Co(acac)(2) as controlling agent, is reported. Polymerizations of monomers with methyl, ethyl, and butyl substituents are fast, reaching high monomer conversion in ethyl acetate as solvent at 30 degrees C, and afford structurally well-defined hydrophobic poly(ionic liquid)s (PILs) of N-vinyl type. Block copolymer synthesis is also achieved by sequential OMRP of N-vinyl-3-alkyldazolium salts carrying different alkyl chains and different counteranions (Tf2N- or Br-). These block copolymerizations are carried out at 30 degrees C, either under homogeneous solution in methanol or in a biphasic medium consisting of a mixture of ethyl acetate and water. Unprecedented PIL-b-PIL block copolymers are thus prepared under these conditions. However, anion exchange occurs at the early stage of the growth of the second block. Finally, diblock copolymers generated in the biphasic medium can be readily coupled by addition of isoprene, forming all PIL-based and symmetrical ABA-type triblock copolymers in a one-pot process. Such a direct block copolymerization method, involving vinylimidazolium monomers bearing different alkyl chains, thus opens new opportunities in the precision synthesis of all PIL-based block copolymers of tunable properties.

International audience; The Bronsted acid-catalyzed polytransacetalization of hydroxymethylbenzaldehyde dimethylacetal (1), a commercially available AB(2)-type monomer, led to hyperbranched polyacetals (HBPA's) with a degree of branching (DB) around 0.5 by forming methanol as byproduct. In sharp contrast, the polyacetalization of the nonprotected homologue, namely, hydroxymethylbenzaldehyde (2), yielded HBPA's with DB = 1, by forming water as byproduct, under the same acidic conditions. This major difference arises from the instability of the initially formed hemiacetal intermediates, which react faster than aldehyde moieties, driving the polyacetalization toward the quantitative formation of dendritic acetal units. This represents a rare example of defect-free hyperbranched polymer synthesis utilizing a very simple AB(2)-type monomer. Bronsted acid catalysts included p-toluenesulfonic, camphorsulfonic, and pyridinium camphorsulfonic acids. Trapping of the water generated during polyacetalization of 2 was accomplished using molecular sieves regularly renewed, which allowed achieving polymers of relatively high molar masses. These HBPA's with DB = 1 featuring multiple aldehyde functions at their periphery were further derivatized into PEGylated HBPA's, using linear amino-terminated poly(ethylene oxide)s of different molar masses. This led to submicrometric sized HBPA's with a core shell architecture. Finally, HBPA derivatives could be readily hydrolyzed under acidic conditions (e.g., pH = 4), owing to the acid sensitivity of their constitutive acetal linkages.

International audience; Several commercial trialkyl phosphines were tested as organic catalysts for the group transfer polymerization (GTP) of methyl methacrylate (MMA) and tert-butyl acrylate (tBA). Among them, only tris(2,4,6-trimethoxyphenyl)-phosphine (TTMPP) was able to bring about the "controlled/living" GTP of both monomers at room temperature, in bulk and/or in THF solution, using 1-methoxy-2-methyl-1-[(trimethylsilyl)oxy]prop-1-ene (MTS) as initiator. However, control of the polymerization appeared to be more difficult in the case of tBA compared to MMA. Poly[alkyl(meth)acrylate]s exhibiting dispersities

International audience; The synthesis of poly(N-heterocyclic carbene)s, denoted poly-(NHC)s, and of their poly(NHC-CO(2)) adducts for a use in organocatalysis is described. Poly(NHC)s were readily obtained in a three-step sequence of reactions, involving i) the free-radical polymerization of ionic liquid monomers, that is, 1-vinyl-3-alkylimidazolium-type monomers with bromide (Br(-)) as counteranion, followed by ii) anion exchange of Br(-) for bis(trifluoromethanesulfonyl)imide ((-)NTf2), of the poly(1-vinyl-3-alkylimidazolium bromide) precursors, affording poly(1-vinyl-3-alkylimidazolium bis(trifluorornethanesulfonyl)imide) derivatives, and iii) deprotonation of the latter polymeric ionic liquids with a strong base. Carbon dioxide (CO(2)) was found to reversibly react with poly(NHC)s forming relatively air-stable and thermolabile poly(NHC-CO(2)) adducts. Both poly(NHC)s and their poly(NHC-CO(2)) adducts were used as polymer-supported organic catalysts and precatalysts, respectively, in transesterification and benzoin condensation reactions under homogeneous conditions. Both types of polymer-supported NHCs were recycled and used several times, but the manipulation of poly(NHC)s like their molecular NHC analogues-was more complicated owing to their air and moisture sensitivity. In this regard, zwitterionic poly(NHC-CO(2)) adducts like their molecular NHC-CO(2) analogues could be easier manipulated than their bare poly(NHC) counterparts, providing good to excellent yields even after several organocatalytic cycles, in particular toward the transesterification reaction.

International audience; The aqueous solution behavior of novel polypeptide-based double hydrophilic block copolymers (DHBCs), namely, poly[2-(dimethylamino)ethyl methacrylate]-b-poly(glutamic acid) (PDMAEMA-b-PGA), exhibiting pH- and temperature-responsiveness is presented using a combination of scattering techniques (light and neutron) and transmission electron microscopy. Close to the isoelectric point (IEP), direct or inverse electrostatic polymersomes are generated by electrostatic interactions developing between the two charged blocks and driving the formation of the hydrophobic membrane of the polymersomes, with the latter being stabilized in water by uncompensated charges. Under basic conditions, that is, when PDMAEMA is uncharged, the thermosensitivity of the DHBCs relates to the lower critical solution temperature (LCST) behavior of PDMAEMA around 40 degrees C. As a consequence, at pH = 11 and below this LCST, free chains of DHBC unimers are evidenced, while above the LCST the hydrophobicity of PDMAEMA drives the self-assembly of the DHBCs in a reversible manner. In this case, spherical polymeric micelles or polymersomes are obtained, depending on the PGA block length. These possibilities of variation in size and shape of morphologies that can be achieved as a function of temperature and/or pH variations open new routes in the development of multiresponsive nanocarriers for biomedical applications.

International audience; 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 alpha,omega-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 alpha,omega-difunetionalized PEOs by combined techniques such as H-1 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 alpha- and omega-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 alpha-Nu,omega-OE PEO chain (activated chain end mechanism).

International audience; 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, ovoids, 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.

International audience; Three imidazolium-based ionic liquid (IL) monomers, namely, 3-(1-ethyl imidazolium-3-yl)propylmethacrylamido bromide (IL-1), 2-(1-methylimidazolium-3-yl)ethyl methacrylate bromide (IL-2), and 2-(1-ethylimidazolium-3-yl)ethyl methacrylate bromide (IL-3), and methacrylic acid (MAA) were polymerized by the reversible addition fragmentation chain transfer (RAFT) process in methanolic solutions at 70 °C, using either 2-cyanopropyl dithiobenzoate (CTA-1) or (4-cyanopentanoic acid)-4-dithiobenzoate (CTA-2) as chain transfer agents (CTAs). Under these conditions, polymers exhibited molar masses predetermined by the initial molar ratio of the monomers to the dithioester precursor, as evidenced by 1H NMR spectroscopy from chain ends analysis. These hydrophilic polymers were subsequently used as macro-CTAs in chain extension experiments in aqueous or in alcoholic solutions, affording IL-based double hydrophilic block copolymers (DHBCs) of the type PIL-1-b-PAm, PMAA-b-PIL-2 and PMAA-b-PIL-3, where PAm and PIL stand for polyacrylamide and polymeric ionic liquid. These DHBCs could be further manipulated and made to self-assemble in micelle-like structures in water by exchanging the bromide (Br−) counteranion of IL blocks for −N(SO2CF3)2. This anion exchange indeed turned the solution properties of the PIL blocks from hydrophilic to hydrophobic, as verified on the corresponding IL-based homopolymers which were immiscible with water after the anion switch. Investigations by 1H NMR evidenced that the diblock copolymers exhibited salt-responsive behavior in aqueous solutions: anion exchange induced the formation of water-soluble micellar aggregates consisting of hydrophobic − N(SO2CF3)2-based IL blocks at the core stabilized by water-soluble PAm or PMAA at the shell.

International audience; Both AB linear-type and AB(2) miktoarm star-type amphiphilic block copolymers based on polystyrene (PS) as A block and poly(glutamic acid) (PGA) as B block were obtained by a four-step synthetic approach combining (i) atom transfer radical polymerization of styrene and (ii) chemical modification of the bromo end groups of ATRP-derived precursors into many or twice as many primary amino groups, followed by (iii) ring-opening polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride and (iv) a final step of hydrolysis. The self-assembly properties in bulk of these linear PS-b-PGA and miktoarm star PS-b-(PGA)(2) block copolymers were subsequently investigated by different analytical means, including Fourier transform infrared spectroscopy (FTIR), wide and small-angle X-ray scattering (WAXS and SAXS) and atomic force microscopy (AFM). FTIR analysis revealed that the PGA block systematically adopted a rodlike alpha-helix conformation, even for degree of polymerization as low as 18. The very high immiscibility between PS and PGA blocks (conformational asymmetry) drove all of these rod-coil block copolymers to self-assemble in a hexagonal in lamellar (HQ morphology in the nanometer size range, whatever their composition and architecture. In addition, WAXS and SAXS results evidenced the effect of the macromolecular architecture on the local organization of PGA helices: the linear block copolymers showed an internal lamellar structure with PGA helices stacked, inter-digitated or folded depending on the weight fraction of the rodlike PGA blocks, whereas miktoarm stars exhibited a stacked microstructure, independently of the PGA content

National audience; Double hydrophilic block copolymers (DHBC) consisting of a Jeffamine block, a statistical copolymer based on ethylene oxide and propylene oxide units possessing a lower critical solution temperature (LCST) of 30 degrees C in water, and Poly(L-glutamic acid) as a pH-responsive block were synthesized by ring-opening polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride using an amino-terminated Jeffamine macroinitiator, followed by hydrolysis. This DHBC proved thermoresponsive as evidenced by dynamic light scattering and small-angle neutron scattering experiments. Spherical micelles with a Jeffamine core and a poly(L-glutamic acid) corona were formed above the LCST of Jeffamine. The size. of the core of such micelles decreased with increasing temperature, with complete core dehydration being achieved at 66 degrees C. Such behavior, commonly observed for thermosensitive homopolymers forming mesoglobules, is thus demonstrated here for a DHBC that self-assembles to generate thermoresponsive micelles of high colloidal stability.

International audience

Polystyrene (PS)/poly(ethylene oxide) (PEO) amphiphilic star-block copolymers and dendrimer-like architectures were prepared using a core-first method. PS stars were first obtained by atom transfer radical polymerization using three and four functional benzyl halides. The chain ends of these star polymers were subsequently modified to generate either the same or twice the number of hydroxyl groups that served to grow the PEO blocks by anionic polymerization of ethylene oxide. Well-defined PSn-b-PEOn (n = 3 or 4) stars and PS3-b-PEO6 dendrimer-like copolymers exhibiting a monomodal and narrow molar mass distribution were obtained in this way. When spread at the air/water interface, these stars proved to be surface active, forming stable reproducible films. Isotherms yielded A0 (theoretical surface area occupied by a film at zero pressure) values, allowing for quantitative comparisons between the stars and linear diblock analogues. Both structures demonstrated similar behavior, passing from liquid expanded ...

Star-block copolymers (PEO3-b-PAA3) and dendrimer-like copolymers (PEO3-b-PAA6) consisting of three inner poly(ethylene oxide) (PEO) arms and either three or six peripheral poly(acrylic acid) (PAA) blocks were derived by a core-first approach. To this end, the OH end groups of three-arm PEO stars prepared anionically were derivatized into either three or six bromo-ester functions that served to grow the poly(tert-butyl acrylate) (PtBA) blocks by atom transfer radical polymerization (ATRP) in a controlled fashion. This could be achieved at 80 °C in toluene in the presence of CuBr/pentamethyldiethylenetriamine (CuBr/PMDETA) as the catalyst system. Characterization by size exclusion chromatography and NMR of star-block copolymers (PEO3-b-PtBA3) and dendrimer-like copolymers (PEO3-b-PtBA6) confirmed their well-defined character. Subsequent treatment with trifluoroacetic acid selectively hydrolyzed the PtBA blocks, leading to the targeted PEO3-b-PAA3 and PEO3-b-PAA6 compounds. Alternatively, an arm-first metho...

We studied the effect of the length of alkyl end groups and chain backbone architecture on the associative properties of end-capped PEO. The latter was done by comparing linear and star PEO with th...

AA‘2-type asymmetric stars and AB2-type miktoarm star polymers were prepared by combination of atom transfer radical polymerization (ATRP) and chemical modification of the termini of ATRP-derived polymers. The first step involved the preparation of ω-bromopolystyrene (PS) chains by ATRP using ethyl 2-bromoisobutyrate as initiator. Styrene was polymerized in bulk at 100 °C in the presence of Cu(I)Br and pentamethyldiethylenetriamine (PMDETA) as catalytic system. Next, the bromo end groups of the resulting PS chains were derivatized into twice as many bromoisobutyrates in order to obtain ω,ω‘-bis(bromo)-PS chains. The last step consisted of growing either two additional PS or two poly(tert-butyl acrylate) (PtBA) blocks by ATRP, following the same polymerization conditions as those mentioned above. This methodology enabled us to synthesize AA‘2 triarm PS stars with asymmetry in the molar mass of their branches and PS(PtBA)2 stars with chemically different PS and PtBA arms. According to the evolution of molar...

Novel multihalide compounds which were readily obtained by derivatization of 4-tert-butylcalix[4,6,8]arenes were used to initiate the atom transfer radical polymerization (ATRP) of styrene, tert-butyl acrylate (t-BuA), and methyl methacrylate (MMA), in the presence of CuX (X = Br or Cl) and 2,2‘-bipyridyl. Well-defined polystyrene (PS) stars constituted of precisely four, six, and eight arms could be synthesized with a narrow polydispersity in this way. For instance, octafunctional polystyrene stars exhibiting molar masses as high as 600 000 g mol-1 could be prepared. However, the polymerization had to be restricted to low conversion, typically below 15−20% to prevent stars from mutually coupling and avoid their contamination with species of higher functionality. Besides the concentration of polymeric radicals [P•], the factor that was found to play a significant role in the occurrence of star−star coupling is their overlapping concentration (C*): intermolecular coupling indeed appeared to be enhanced whe...

Newly designed star-shaped and dendrimer-like copolymers made of poly(ethylene oxide) (PEO) and polystyrene (PS) were synthesized by sequential anionic polymerization of ethylene oxide and atom transfer radical polymerization (ATRP) of styrene, the switch from the first to the second mechanism being obtained by selective transformation of “living” oxanionic sites. First, tri- and tetrafunctional initiators were used to anionically polymerize ethylene oxide and produce tri- and tetraarmed PEO stars. Next, the OH end groups of PEO star branches were derivatized into 2-bromopropionate groups giving rise to the corresponding tri- and tetrabromoester ended-PEO stars; the latter served as macroinitiators for the ATRP of styrene at 100 °C in the presence of CuBr/2,2‘-bipyridine catalyst system affording amphiphilic star block copolymers PEOn-b-PSn (n = 3 or 4). PEOn-b-PS2n (n = 3 or 4) dendrimer-like copolymers constituted of an inner PEO part and an outer PS layer were prepared by introducing a branching agent ...

A novel octafunctional calixarene derivative, namely, 5,11,17,23,29,35,41,47-octa-tert-butyl-49,50,51,52,53,54,55,56-octakis(2-bromopropionyloxy)calix[8]arene (1) which was readily synthesized in one step, was used to initiate the bulk atom transfer radical polymerization (ATRP) of styrene, at 100 °C, in the presence of CuBr/2,2‘-bipyridyl. Polystyrene (PS) stars of narrow polydispersity with precisely eight arms could be synthesized by restricting the polymerization to low conversion, typically below 15−20%. At higher conversions, irreversible coupling occurred between stars as evidenced by a size exclusion chromatography line equipped with a multiangle laser light scattering detector (MALLS/SEC). Octafunctional stars of molar masses up to 340 000 g mol-1 could be prepared by using high ratios of the monomer to the initiator ([M]/[I] = 12 000). The precise octafunctional structure of the stars was confirmed, on one hand, by studying the kinetics of ATRP of styrene initiated by an equimolar mixture of 1 a...

A C60 derivatized triarm poly(ethylene oxide) copolymer was synthesized and characterized. The soluble polymer produced spread at aqueous interfaces to form highly expanded fluid Langmuir monolayers. The onset area of 1300 A2/arm is likely due to the polymer disrupting cohesion between C60 units. Compression/expansion studies revealed a significant elastic region, beyond which the C60 units condensed, and a compact rigid and irreversible monolayer formed.

The tetramine ligand 1 hexasubstituted by very long alkyl chains (C18H37) exhibits an exceptionally large temperature-dependent solubility in 1,4-dioxane, its solubility increasing ca. approximately 104-fold between 23 and 50 degrees C. The preformed copper(I) complex CuBr/1 was shown to catalyze the atom transfer radical polymerization of methyl methacrylate with good control of the molar masses and polydispersities. Due to the thermoresponsive character of CuBr/1 polymerizations were carried out in homogeneous conditions while lowering the temperature to 10 degrees C led to the precipitation of the catalyst. Catalyst recovery was achieved with high yield ( approximately 95%) by a simple filtration under noninert atmosphere. Very low residual copper contamination ( approximately 200 ppm) was measured in the final polymer. The catalyst was recycled two times without significant loss of activity.