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International audience; PScomb-block-PEOcomb copolymers having a poly(chloroethyl vinyl ether)-b-poly(hydroxy ethyl vinyl ether) backbone with polystyrene chains on one side and poly(ethylene oxide) chains on the other, i.e. (PCEVE-g-PS)-b-(POHEVE-g-PEO), were synthesized. The strategy is based on grafting of polystyryllithium onto the reactive chloro functions of the poly(chloroethyl vinyl ether) first block and on grafting polyethylene oxide from the hydroxyl functions of the second block. This procedure allows the preparation of densely grafted amphiphilic diblocklike, Janus-type, comblike copolymers with high molar masses and narrow polydispersity. The characteristics and dimensions of isolated (PCEVE-g-PS)-b-(POHEVE-g-PEO) macromolecules were studied by light scattering in THF, a good solvent of both PS and PEO branches, as well as using AFM imaging of highly diluted deposits. Unimolecular rodlike nano-objects with distinct PS and PEO domains were observed, in agreement with their diblocklike structure. In relation with their amphiphilic nature, the combs can self-assemble in different morphologies. When graphite deposits are made from more concentrated methylene dichloride solutions, the PScomb-b-PEOcomb copolymers self-assemble directly on the substrate, forming flowerlike molecular aggregates interconnected by their PEO moieties. When deposits are made from a selective solvent (methanol) of the PEO comb block, hyperbranched micelles formed in the solution retain their structure on the solid substrate, yielding well-defined spherical objects.

International audience; Comblike block copolymers having a poly(chloroethyl vinyl ether) backbone and poly(styrene-b-isoprene) side chains, i.e., PCEVE-g-(PS-b-PI), of different molar masses and chemical compositions were synthesized by "grafting onto" technique using the coupling reaction of acetal-PSLi (F-PSLi) chains onto the reactive functions of a PCEVE backbone, followed, in a second step, by the grafting of living PIDLi chains onto the acetal ends of PS branches activated by trimethyl silyl iodide. The comblike copolymers exhibit low polydispersity, high molar masses, and a controlled number of branches. Their characteristics and behavior were further studied in the solid as thin films and in good and selective solvents. Atomic force microscopy (AFM) shows isolated uniform molecules that adopt an ovoid conformation. The solution behavior of these comblike polymers was investigated by dynamic light scattering (DLS), both in a good solvent of the PS and the PI blocks and in selective solvents of the outer PI blocks. Depending on the solvent quality and the temperature, the comblike copolymers, which remain in the form of isolated molecules, adopt different chain conformations and dimensions, as shown by the drastic variation of the radius of gyration. In a series of hydrocarbon solvents of decreasing quality for the inner PS block, the significant volume decrease of the macromolecule is attributed to the internal shrinkage of the PS blocks. In cyclohexane, a theta solvent for the inner PS block, a strong variation of the comblike size (90% volume change) takes place with the temperature change, directly correlated with the internal expansion/contraction of the inner PS blocks.

International audience

International audience

International audience; We report on the synthesis of large and densely tough dendrimer-like star-branched polystyrenes of generation 3, specially designed for their visualization by AFM imaging. For this purpose, an iterative methodology involving a sequential three stages synthetic approach has been adopted. The precisely designed G-3 polymers appear on AFM images as completely flattened objects with a symmetrical square-like shape and an average diameter of 250 nm and a height of less than 1 nm. Imaging of their internal structure indicates that they are constituted of four interconnected lobes, in relation with the use of a tetrafunctional core precursor. In addition, AFM images show the presence inside each object of all the branching points which appear as white harder zones regularly distributed in the less dense and softer PS matrix.

International audience; Synthesis of dendrimer-like star-branched poly(ethylene oxide)s (PEOs) with two and three generations having Zn(II) tetraphenylporphyrin (ZnTPP) moieties at the core and at each branching point has been successfully achieved through an iterative convergent approach harnessing "click chemistry". In the first step, a four-armed poly(ethylene oxide)star-shaped polymer was synthesized by the copper(I)-catalyzed azide-alkyne cycloaddition between alpha-azido poly(ethylene oxide) branches (N-3-PEO-OH) and 5,10,15,20-tetra(propargyloxyphenyl) Zn(II) porphyrin as the core. In the second step, a tetra-armed star PEO bearing 5-(4-phenoxy)-10,15,20-tris(propargyloxyphenyl) Zn(II) porphyrin at each branch end was prepared by divergence of the omega-hydroxyl PEO chain-ends through a Williamson-type etherification reaction. The resulting star PEO with 3 propargyl groups at each arm end was then subjected to a new "click chemistry" reaction with N-3-PEO-OH affording the dendrimer star-like PEO of second generation carrying 12 new omega-OH-PEO external branches attached to the four ZnTPP branching points. Repetition of the second step afforded the high molar mass third generation dendrimer-like PEO carrying 36 omega-OH PEO terminal branches with a uniform distribution of 17 zinc tetraphenylporphyrin moieties as internal branching points. The photophysical properties of the resulting polymers in organic or aqueous medium and their efficiency in singlet oxygen generation are reported.

International audience; New hydrogels were prepared from iron(III) tetraphenylporphyrinato-functionalized 4-arm poly(ethylene oxide) films in which water plays both the role of a cross-linker and a swelling agent. Depending on the pH conditions, the hydrogels present the feature of either a chemical network or that of a dynamic transient network. Importantly, this intriguing behaviour is fully reversible as evidenced by rheological analysis and solubility tests.

International audience; The synthesis of Janus like comb copolymers constituted of polystyrene and poly(methyl vinyl ether) branches attached to a diblock backbone has been achieved using living/controlled cationic and anionic building steps associated to grafting from and grafting onto coupling processes. These comb-b-comb structures behave as isolated objects in good solvents as well as when deposited on an appropriate substrate from a good solvent. In contrast, thanks to their amphiphilic Janus-like structure, they behave like linear diblock copolymers when placed in a selective solvent of one of the comb moieties, forming stable large spherical super-micelles that could be observed on mica support.

International audience; A series of the fourth-generation (4G) dendrimer-like star-branched poly(methyl methacrylate)s, (PMMA)s, with high branch densities have been synthesized by the iterative "arm-first" divergent methodology. It involves a two-reaction sequence in each iterative process: (1) a linking reaction of alpha-functionalized living anionic PMMA with either two or four tert-butyldimethylsilyloxymethylphenyl (SMP) groups with benzyl bromide (BnBr)-chain-end-functionalized PMMA and (2) a transformation reaction of the SMP groups into BnBr functions. Accordingly, the branch segments are introduced by the (1) linking reaction based on termination reaction using premade living anionic polymers. The two-reaction sequence has been repeated four times to build up the 4G dendrimer-like star-branched polymers composed of four branch junctures in three generations and two branch junctures in one generation. Likewise, three block copolymers with the same dense 4G branched architectures have been synthesized by the linking reaction of the 3G brominated PMMA with either of living anionic polymers of tert-butyl methacrylate, (2,2-dimethyl-1,3-dioxolan-4-yl)methyl methacrylate, and 2-vinylpyridine. Unfortunately, however, the synthesis of a highly dense 4G polymer composed of four branch junctures in all generations was not successful possibly due to steric hindrance. The resulting dendrimer-like star-branched (PMMA)s have been analyzed by RALLS, SAXS, and viscosity measurements to obtain their hydrodynamic radii, radii of gyration, intrinsic viscosities, and g' values. The relationship between either of such values and the branched structures, generation, or molecular weight will be discussed. The observation of the largest and most dense 4G polymer by AFM was attempted in order to directly visualize the dendrimer-like star-branched polymer.

International audience; Comblike copolymers with randomly distributed polystyrene (PS) and polyisoprene (PI) branches, i.e., PCEVE-g-(PS, PI), were synthesized by the "grafting onto" technique. The comblike copolymers exhibit a low dispersity, high molar masses, and controlled number of branches. Their characteristics and behavior as isolated objects were investigated as solid molecular deposits, using atomic force microscopy (AFM), and in solution, in a good solvent of the polystyrene and polyisoprene branches, using dynamic light scattering (DLS). AFM experiments show isolated uniform molecules that adopt an ovo'idal conformation whose dimensions are found in good agreement with DLS data. The self-organization of the PS, PI comb copolymers was further studied in the solid state as thin films, using SAXS. The results show that PCEVE- g-(PS, PI) combs yield lamellar biphasic morphologies that were compared to those observed for PCEVE-g-(PS-b-PI) combs with PS-b-PI diblock branches and those known for linear PS-b-PI of similar weight compositions.

International audience

International audience; Large macrocyclic poly(chloroethyl vinyl ether)s (PCEVE)s of controlled ring size and narrow distribution were synthesized by a ring-closure process involving the intramolecular formation of acetal linkages between the two external blocks of linear ABC triblock precursors prepared by living cationic polymerization. The corresponding shape-persistent ring P(CEVE-g-PS) combs having macrocyclic poly(chloroethyl vinyl ether) backbones and polystyrene side chains were then synthesized by a “grafting onto” technique and characterized by size exclusion chromatography (SEC) analysis and atomic force microscopy (AFM) imaging of isolated molecules. Quantitative hydrolysis of the acetal linkages of the macrocyclic PCEVE backbone in acidic conditions yields the linear poly(chloroethyl vinyl ether)-g-polystyrene) homologue and allows a direct comparison of the characteristics and dimensions of cyclic and linear comb architecture. The influence of the chain architecture and PS graft dimensions on the dilute tetrahydrofuran (THF) solution properties, radius of gyration, and hydrodynamic radius of the comb copolymers is also studied and compared to data reported for linear and cyclic polystyrene chains.

We report on an efficient route to design large macrocyclic polymers of controlled molar mass and narrow dispersity. The strategy is based on the synthesis of a triblock copolymer A B C, in which the long central block B is extended by two short A and C sequences bearing reactive antagonist functions. When reacted under highly dilute conditions, this precursor produces the corresponding macrocycle by intramolecular coupling of the A and C blocks. Chloroethyl vinyl ether was selected as the monomer for the central block B , because it can be readily derivatized into brushlike polymers by a grafting process. The corresponding macrocyclic brushes were decorated with polystyrene or randomly distributed polystyrene and polyisoprene branches. In a selective solvent for the polyisoprene branches, the macrocyclic brushes self-assemble into cylindrical tubes of up to 700 nanometers.

International audience; Poly(styrene)comb-b-poly(isoprene)comb copolymers having a heterofunctional polyvinyl ether diblock backbone were synthesized by the grafting onto method. Their synthesis involves in a first step the selective coupling reaction of polystyryllithium chains onto the reactive chloroether functions of a poly(chloroethyl vinyl ether) first block while the second block poly(pyranethoxy vinyl ether) remains unchanged, yielding Poly(styrene)comb with a poly(pyranethoxy vinyl ether) tail. In a second step, living polyisoprenyllithium chains are grafted onto the second block previously modified to introduce reactive chlorobutyl functions. The obtained high molar masses PScomb-b-PIcomb copolymers exhibit a low polydispersity and a controlled number of branches. Their characteristics and behavior were further studied as isolated objects using imaging technique such as atomic force microscopy and using light scattering in a good solvent for PS and PI moieties, and in a selective solvent of PIcomb blocks. The PScomb-b-PIcomb copolymers adopt a cylindrical conformation in good solvent and self-assemble in micelles by association of the combPS blocks in heptane.

ISSN: 1598-5032; International audience; Living anionic and cationic polymerizations have been combined to prepare various types of comb-like copolymers composed of polystyrene (PS) and polyisoprene (PI) blocks, with a precisely controlled architecture. According to the relative placement of these elementary building blocks, combs with randomly distributed PS and PI or with poly(styrene-b-isoprene) diblock branches (I & II, respectively) can be prepared. The reaction procedure initially includes the synthesis of a poly(chloroethylvinyl ether) using living cationic polymerization, which is used as the reactive backbone to successively graft PS-Li+ and PI-Li+ or PI-b-PS-Li+ to obtain structures (I) or (II). The synthesis of Janus-type PS-comb-b-PI-combs (III) initially involves the synthesis of a diblock backbone using living cationic polymerization, which bears two distinct reactive functions having either a protected or activated form. Living PS-Li+ and PI-Li+ are then grafted, in two separate steps, onto each of the reactive functions of the backbone, respectively.

International audience; The synthesis of a series of water-soluble galactopyranose-functionalized polystyrene-polyvinyl ether dendrigrafts and their characterization (in solution and thin solid deposits) have been achieved. The presence of external galactopyranose groups on dendritic polymers has been exploited to prepare dendrigraft-oligonucleotide conjugates using a simple one-step coupling procedure with amino-ended oligonucleotides (ODNs). Several parameters such as the peripherical density of hydrophilic branches, the polymerization degree of polystyrene or poly(hydroxyethyl vinyl ether) blocks, and the number of galactopyranose groups were tuned. A capture test with short labeled complementary ODNs (25 bases) confirmed the presence of covalently bound ODNs on various kinds of dendrigrafts. The ability of the dendritic polymers to enhance the sensitivity of enzyme-linked oligosorbent assay (ELOSA) diagnostic tests (detection of hepatitis B virus, DNA target of 2400 bases) was then evaluated, especially the influence of the macromolecular architecture and the impact of the structural parameters. The dendrigraft-ODN conjugate with the lower saccharide external density was found to lead to a very significant amplification of the fluorescence signal, corresponding to a limit of sensitivity of 10(9) DNA copies per milliliter (instead of 10(11) DNA copies per milliliter without using dendrigrafts). Conversely, the dendrigrafts exhibiting a very high number of branches and galactopyranose groups at their periphery were not able to induce a better sensitivity due to steric hindrance generated by the peripheral congestion on these polymers.

International audience; The morphology of micelles formed from blends of linear and cyclic poly(styrene-b-isoprene) (PS-b-PI) block copolymers has been investigated in solution using dynamic light scattering (DLS) and in thin solid deposits by atomic force microscopy (AFM) and transmission electron microscopy under cryogenic conditions (cryo-TEM). Micelles of the pure cyclic PS290-b-PI110 copolymers are wormlike cylindrical objects built by unidirectional aggregation of 33 nm wide sunflower micelles, while the linear block copolymer having the same volume fraction and molar mass forms spherical micelles 40 nm in diameter. The DLS, AFM, and cryo-TEM results consistently show that the addition of the linear copolymer (even for amounts as low as 5% w/w) to the cyclic copolymer rather favors the formation of spherical micelles at the expense of the cylindrical aggregates. Those results clearly show that the linear block copolymer chains can be used to stabilize the thermodynamically unstable elementary sunflower micelle. The thermal stability of the micelles (from the pure copolymers and from the blends) has been examined in solid deposits with in situ AFM measurements. Coalescence starts at about 70 degrees C, and the surface roughness shows a two-step decrease toward a fully homogeneous and flat structure.

International audience; Water-soluble amphiphilic dendrigrafts constituted of a hydrophobic polystyrene core and a hydrophilic poly(ethylene oxide) shell have been prepared via a 'grafting onto' procedure from polystyrene dendrigraft precursors. The introduction of the surrounding hydrophilic shell was achieved through cyclic trans-acetalization between omega-acetal functionalized branches of the polystyrene precursor and PEO grafts bearing a alpha-bis(hydroxymethyl) chain end (A(2)-PEO). Yields of grafting are strongly affected by the increase of the degree of polymerization of the reactive PEO grafts (respectively, 100, 87, and 38% with A(2)-PEO20, A(2)-PEO100 and A(2)-PEO150). However, paradoxically, only the use of A(2)-PEO100 or A(2)-PEO150 as reactive grafts affords water-soluble dendrigrafts due to higher PEO weight content (respectively, 41 and 36%). The dimensions and the shape of the PScore-PEOshell Polymers were investigated in solution (THF and water) by dynamic light scattering and in the dry state by TEM and AFM.

International audience; We have studied the effect of polystyrene (PS) homopolymer addition on the morphology of self-assembled block copolymer micelles made from linear or cyclic poly(styrene-b-isoprene), PS-b-PI, in a selective solvent for the PI block (heptane). Both copolymers have the same composition: the degree of polymerization is 290 for the PS block, and 110 for the PI block, and we focused on the influence of the addition of small amounts of PS homopolymer on the micellar morphology. For the copolymer concentrations considered, the linear copolymer self-organizes into spherical micelles while the cyclic copolymer forms cylindrical micelles. PS and PI chains constitute the core and the corona of these micelles, respectively, due to the different affinity of the blocks for heptane. Consequently, the PS homopolymer added is "solubilized" into the micellar core. Dynamic light scattering (DLS) data combined with atomic force microscopy (AFM) results show that the addition of PS homopolymer induces a drastic change in the micellar organization. Indeed, a morphological transition, from spheres to cylinders for the linear copolymer, and from cylinders to vesicles for the cyclic copolymer, is observed. These results highlight the fact that a small incorporation of PS homopolymer is clearly sufficient to modify the morphology (size and shape) of the micelles. This approach could be a key parameter for the design/control of micelles for specific applications in nanotechnology.

International audience; We have studied the morphology of self-assembled micelles made of linear and cyclic poly(styrene-b-isoprene) PS-b-PI block copolymers dispersed in selective solvents of the PI block (n-heptane, n-decane). Up to a copolymer concentration of 5 mg mL(-1), the micelles made from linear block copolymer chains adopt a spherical shape. Those arising from cyclic copolymer chains having exactly the same molar mass and volume fraction self-assemble into (i) planar sun. ower-shaped particles at low concentration (c < 0.1 mg mL(-1)), (ii) giant wormlike micelles at intermediate concentration (0.1 mg mL(-1) < c < 2 mg mL(-1)) and (iii) vesicles at higher concentration (2 mg mL(-1) < c < 5 mg mL(-1)). Those results were obtained using dynamic light scattering and in situ freeze-drying cryo-transmission electron microscopy. In this contribution, we discuss the effects of concentration and temperature on the morphology of the self-assembled particles made from both linear and cyclic PS-PI copolymers, and highlight the surprising vesicle formation in cyclic block copolymer solutions.