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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.

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The synthesis, characteristics, and properties of amphipatic, water-soluble dendrigrafts, with a polystyrene core and polystyrene-b-poly(methyl vinyl ether) (PS-b-PMVE) diblock as external branches, are described. The dendrigrafts are observed by AFM and TEM as egglike or long cylindrical objects which can self-organize intramolecularly in segregated subdomains forming flowerlike or strings of flowerlike objects. In organic solvents the dendrigrafts behave as fully soluble isolated macromolecules and show in water a low critical solubility temperature (LCST) at t30 degrees C. The ability of the amphiphilic PS-b-PMVE dendrigrafts to complex and transport in water organic (pyrene) and metallo-organic (manganese tetraphenyl porphyrin) molecules is investigated. The possibility to stabilize the high oxidation state of metallo-porphyrin complexes through their encapsulation into the dendrigraft is shown.

Newly prepared water-soluble amphipatic hyperbranched organic polymers are used as nanocontainer and as carriers for large metal-organic molecules such as metallo-porphyrins. The hydrosoluble dendrigrafts are constituted by a polystyrene hydrophobic core surrounded by a polyvinyl ether hydrophilic shell. These nanometer-sized amphipatic macromolecules with an average diameter of about 100 nm and narrow polydispersity are fully soluble in aqueous media. Their capacity to encapsulate and transport metallo-porphyrins in aqueous media is investigated. Complexation studies show that up to several thousands of guest molecules can be embedded into each amphipatic dendrigraft macromolecule.

This work deals with the study of comb-like vs. arborescent grafted copolymers made of poly(chloroethyl vinyl ether)-g-polystyrene (PCEVE-g-PS). We describe how the molecular architecture of the branched polymers affects their nanoscale organization in thin films, as observed using atomic force microscopy. The results indicate that modifying the molecular architecture from a ‘generation-zero’ comb-like (PCEVE-g-PS) to a ‘first-generation’ hyperbranched (PCEVE-g-(PS-b-PCEVE-g-PS)) architecture strongly modifies the observed geometrical parameters of the molecules, in good agreement with the expected evolution of the molecular dimensions and the corresponding data obtained in solution. The surface organization of the (PCEVE-g-PS) copolymer molecules is also strongly conditioned by the interplay between the molecule–substrate interactions and the molecule–molecule interactions, leading to different possible orientations of the lateral branches with respect to the surface and thus to different final morphologies.

We study the effect of the cyclization of a linear poly(styrene-b-isoprene) PS−PI copolymer on the morphology of the micelles formed in heptane (a selective solvent for PI). The linear and the cyclic copolymers have exactly the same degree of polymerization, i.e. 290 for PS and 110 for PI, i.e., volume fraction ΦPS = 0.78. We use dynamic light scattering (DLS) and atomic force microscopy (AFM) techniques to characterize the micellar morphology made from copolymer molecules, focusing on the effect of cyclization. We also report the concentration effect on the micelle size and shape made from the linear and cyclic copolymers. Our results show that the micelles made from linear PS−PI adopt a “classical” spherical shape and keep the same morphology parameters over the range of investigated concentrations. In contrast, the micelles arising from cyclic copolymer chains adopt a giant wormlike shape. In this later case, both the size and the shape evolve when the concentration is increased, starting from small in...

Cyclic polystyrene-block-polyisoprenes of controlled dimensions have been synthesized for the first time by the direct coupling of α-isopropylidene-1,1-dihydroxymethyl-ω-diethylacetal-heterodifunctional linear polystyrene-block-polyisoprene precursors previously prepared by living anionic polymerization. Cyclization is achieved under high dilution by intramolecular coupling of the polymer ends under acid catalyst conditions. Using this strategy polystyrene-block-polyisoprene macrocycles of controlled chain dimensions are prepared in high yield (> 90%). Pure cycles were finally recovered by flash chromatography. The synthesis and characterization of both the linear α,ω-heterofunctional polystyrene-block-polyisoprenes block copolymers precursors and of the corresponding cyclized chain architectures are reported.

Micelles made from linear polystyrene-block-polyisoprene (PS/PI) in decane are spherical. The differences in the structure of micelles made from linear and cyclic PS/PI were investigated using small-angle X-ray scattering at rest and under shear flow. The effect of shear revealed that micelles made from cyclic copolymer chains have an elongated shape, which was confirmed by transmission electron microscopy. The cyclization of diblock copolymer chains is thus a new method to control the micellar morphology.

Arborescent graft polystyrenes were prepared by the “graft on graft” technique, involving the iterative grafting of end-functional polymer chains onto reactive polymer backbones. The grafts and the reactive backbone building blocks were synthesized individually by living polymerization techniques. The first-generation comb polymers were obtained by the coupling reaction of living α-acetal polystyryllithium onto poly(chloroethyl vinyl ether) PCEVE chains of controlled n. Initiation from acetal termini of polystyrene branches of a new living cationic polymerization of chloroethyl vinyl ether (CEVE) allowed one to prepare the corresponding comb copolymers with polystyrene-b-poly(chloroethyl vinyl ether) branches. Hyperbranched polystyrenes were finally obtained by grafting a second amount of polystyryllithium onto the CEVE units of poly(CEVE) external blocks. Nanomolecules of narrow molar masses distribution, branching functionalities up to 35 000, and molar masses over 108 g/mol were obtained by this method...

The recent emergence of hyperbranched polymers has opened the door to the design of a large variety of new chain architectures that promise to be strong competitors for dendrimers in a variety of potential applications. For instance, «comb-like» polymers can be obtained from poly(chloroethyl vinyl ether)- g -polystyrene (PCEVE- g -PS) copolymers, with excellent control over the dimensions of the polystyrene branches and the PCEVE backbone. In this work, the nanometer scale organization of these materials is studied by means of Atomic Force Microscopy (AFM). We focus on the influence of the intrinsic molecular architecture of the hyperbranched PCEVE- g -PS on the organization of the material. Several parameters such as sample preparation conditions (the nature of the solvent and the substrate, the solution concentration) and annealing of the samples are also taken into account. In the case of very thin deposits, we observe a layer-by-layer organization (the height of one monolayer corresponding to ∼7 nm). On the free surface, it is possible to image single polymer molecules and to analyze their size in terms of the polymer molecular weight. In thicker deposits, the molecules are found to adopt an extended conformation and to form lamellar arrangements.

In this paper, the possibilities offered by anionic polymerization were exploited to engineer well-defined PS-b-PEO2 gemini-type dispersants that were fitted with terminal styrenic groups. Two routes were explored to obtain this novel generation of surfactants whose thorough characterization indicated that they exhibit the expected molecular structure. These reactive block copolymers have been subsequently used as surfactants in the emulsion polymerization of styrene to stabilize the colloidal particles formed. The kinetics of polymerization in the presence of such reactive surfactants were shown to differ from the case involving PS-b-PEO linear macromonomers as surfactants.

The recent emergence of hyperbranched polymers has opened the door for the design of a large variety of novel, well-controlled chain architectures. For instance, «comb-like» and dendritic-like polymers can be obtained from hyperbranched poly(chloroethyl vinyl ether)-g-polystyrene (PCEVE-g-PS) copolymers, with excellent control over the dimensions of the polystyrene lateral branches and the PCEVE backbone. In this work, the nanometer scale organization of these materials is studied by means of Tapping Mode Atomic Force Microscopy. We focus on the influence of the intrinsic molecular architecture of the hyperbranched PCEVE-g-PS on the organization of the material. In the case of thin deposits, we observe a layer-by-layer organization. On the free surface, it is possible to image single polymer molecules and to analyze their size in terms of polymer molecular weight. In most cases, the molecules are found to adopt an extended conformation and to form lamellar arrangements. We observe that the degree of lateral ordering of these molecules strongly depends on their intrinsic architecture.

A series of cyclic poly[(styrene)-b-(ethylene oxide)] diblock copolymers 4 (1.5 kg/mol < M n < 1.1 kg/ mol) with narrow molecular weight distributions (≤ 1.12) have been synthesized. They were obtained by intramolecular cyclization of linear α-diethyl acetal-ω-styrenyl polystyrene ethylene oxide) 3, under high dilution conditions. The use of well-defined linear precursors in association with a cyclization process based on an unimolecular end-to-end coupling reaction allows the formation of macrocyclic diblocks in high yield (more than 90%). The structural characterization and the solution behavior of both the linear and cyclic amphipathic diblock copolymers have been investigated by means of NMR, size exclusion chromatography, and viscosimetry.

In the course of studies dealing with the synthesis and the characterization of the properties of highly branched polymers with controlled chain parameters, the selectivity of the grafting reaction of polystyryllithium chains onto poly(chloroethyl vinyl ether) has been investigated. To that purpose, a series of isometric poly(chloroethyl vinyl ether) oligomers with precise degree of polymerization, ranging from 3 to 9, were prepared by selective fractionation of a poly(CEVE) of narrow polydispersity into its different n-mers. The latter were used as reactive backbone for grafting PSLi chains. Characterization of the graft copolymers shows that the substitution of chloride of CEVE units is quantitative and yields comblike copolymers with a number of branches corresponding to the number of monomer units in the isometric poly(CEVE) backbone. The poly(CEVE)-g-polystyrenes show the typical solution behavior of star polystyrenes.

The grafting of polystyryl lithium onto poly(chloroethyl vinyl ether) chains has been investigated. The reaction proceeds cleanly and quantitatively thus allowing the synthesis of comblike polymers Since the dimensions of the polystyrene branches and of the poly(chloroethyl vinyl ether) backbone can be controlled by living polymerizations, both the length and the number of branches of the graft copolymers can be tuned The latter behave as star polymers. The possibility to initiate a new cationic polymerization of chloroethyl vinyl ether from polystyrene branches bearing acetal termini in order to prepare the corresponding stars with poly(chloroethyl vinyl ether-b- styrene) branches is also examined. Finally access to hyperbranched polymers of controlled architecture and dimensions by deactivation of a second amount of polystyryl lithium onto the last blocks of poly(chloroethyl vinyl ether) is also reported.

The grafting reaction of polystyrene branches onto poly(chloroethyl vinyl ether) (PCEVE) chains, based on the deactivation of polystyryl (PS) carbanionic ends onto chloroethyl ether functions has been investigated. The selectivity of the coupling is very high and allows the almost complete substitution of the chloride group of the CEVE units by PS chains with molar masses up to 15 000. The main side reaction observed is the deactivation of some PS chains, at the very beginning of the reaction. It is attributed mainly to impurities present in the PCEVE solution. Since the PCEVE polymer backbone and the PS grafts can be prepared by both living cationic and anionic polymerization, it is possible to synthesize poly(CEVE-g-styrene) copolymers possessing both a backbone with controlled dimensions and an adjustable number of branches having precise length and narrow molar mass distribution. The synthesis and the characteristics of comblike poly[(chloroethyl vinyl ether)-g-styrene]s are described.

The preparation by living polymerization and the investigation of the properties of polymers with cyclic chain architectures have been recently undertaken. The cyclization involves a unimolecular end-to-end reaction of a heterodifunctional linear precursor The elementary steps of the cyclization mechanism are examined in the light of matrix-assisted laser desorption/ ionization mass spectrometry (MALDI-MS) data obtained on linear polystyrene precursors and cyclized products. The synthetic procedures developed to prepare macrocyclic polymers of various structures, as well as macrocyclic random and block copolymers are then reviewed and discussed. The main characteristics of the cyclic (co)polymers are compared to the corresponding linear chains and some of the original properties that are induced by the cyclic chain architecture are presented.

We recently proposed a new method allowing the controlled synthesis of ring-shaped polymers with predictable molar masses and narrow molar mass distribution. The cyclization is based on a unimolecular “end-to-end” coupling reaction of an heterodifunctional linear polymer precursor. In this paper, this methodology is applied to the synthesis of semicyclic block copolymers comprising a cyclic hydrophilic block on which a linear hydrophobic polymeric tail is attached, i.e., a cyclic diblock copolymer of poly(hydroxyethyl vinyl ether) and linear polystyrene. The general strategy for the synthesis involves three main steps: (i) preparation of a linear α-acetal-γ-styrenyl-poly(chloroethyl vinyl ether-block-styrene) precursor, (ii) intramolecular coupling involving the activation and reaction of the two complementary functions under high dilution, yielding the cyclized poly(CEVE) block, and (iii) substitution by hydroxy functions of the chloro side groups of poly(CEVE) block in order to form the amphiphilic sem...

Since the early 1950s a number of theoretical studies have dealt with the prediction of the dimensions and behaviour of macrocyclic polymers. However, owing to the difficulty of synthesis, the comparison of theories with experimental data still remains restricted to a small number of macromolecules. The first cyclic polymers studied were those produced from systems in which ring-chain equilibrium exists, but it is only in the last decade that a method for the preparation of ring-shaped vinylic polymers of controlled dimensions has become available. The method involves the bimolecular end-to-end ring closure of an anionically prepared α,ω-difunctional linear polymer using a coupling agent. Low cyclization yields are generally observed. Besides theoretical considerations the experimental conditions which may lead to these results have been examined. In this paper a new approach to the synthesis of macrocyclic polymers with controlled dimensions is examined. In contrast to previous procedures, it involves a single unimolecular ring-closure process which is much less sensitive to the extremely low concentrations required for cyclizations. It is achieved by the direct end-coupling of an α,ω-heterodifunctional linear polymer precursor after the appropriate activation under high dilute conditions of one of its two end-functions. The advantages of this new approach are discussed both on theoretical and experimental grounds. Its application to the preparation of poly(vinyl ether)s, polystyrenes and poly(vinyl ether-b-styrene) diblock copolymers of controlled dimensions with a macrocyclic architecture is described.

α-Halogeno ether species, in appropriate conditions, can induce the “living” cationic polymerization of vinyl ethers. They can also be used as initiators for the “living” polymerization of styrene derivatives. Therefore, their use as intermediates in the preparation of tailor-made polymers and copolymers offers interesting opportunities in macromolecular synthesis. The main parameters which determine and control their reactivity are reviewed and discussed. The possibility to generate quantitatively these derivatives by various routes and from different organic functions such as aldehyde, ketone, acetal and hydroxyl is examined. Some of these routes have been used to generate the α-halogeno ether function directly at the end of acetal and hydroxy-terminated polymers. The latter have then been used as macroinitiators to prepare new block copolymers. The synthesis of poly(isobutyl vinyl ether-β-ethyl vinyl ether), poly(styrene-β-chloroethyl vinyl ether) and poly(chloroethyl vinyl ether-β-butadiene-β-chloroethyl vinyl ether) by this technique is described.

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.

The preparation and characteristics of a series of comb (co)polymers with different chain architectures and/or topologies are described. These structures are based on the preparation of poly(chloroethyl vinyl ether) (PCEVE) as a reactive backbone, which is used for grafting living anionic chains, typically polystyryllithium or polyisoprenyllithium. Since these different building blocks are synthesized by living ionic polymerizations, a precise control of the dimensions of both the branches and the backbone can be achieved, whereas the selectivity of the branch coupling reaction permits an almost quantitative substitution of the chloride groups of the PCEVE chain. This approach allows to precisely tune the dimensions and structure of the corresponding macromolecules and comb architectures displaying very different shapes. Linear, star-like, cylindrical, ringlike, have been prepared and characterized by different techniques including AFM imaging.

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.

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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 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; 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.

One of the most interesting and fascinating solution properties of block copolymers is their ability to self-assemble into micelles, lamellar aggregates, and vesicles. Such organized structures have made diblock copolymers of great importance in nanotechnology applications.1-11 For instance, the spontaneously formed vesicles in water are potentially useful as vehicles for delivering drugs and as biomimetic models of biological cells. We show here for the first time that the cyclization of a linear copolymer chain induces a remarkable change in the micellar morphology. This result is highlighted in the case of linear and cyclic polystyrene−polyisoprene (PS−PI) diblock copolymers having exactly the same molar weight and dispersed in a selective solvent for PI. The micelles arising from linear diblock copolymers exhibit a monodisperse spherical shape (50 nm in diameter) whereas those formed from cyclic copolymers are long (>1 μm) cylindrical (wormlike) objects resulting from the unidirectional self-assembly ...

New water-soluble amphipatic hyperbranched organic polymers composed of a hydrophobic polystyrene core and a hydrophilic shell have been synthesized and characterized. An arborescent polystyrene core is first synthesized by the “graft-on-graft” technique based on the iterative grafting of end-functional polystyryllithium chains onto reactive poly(chloroethyl vinyl) ether backbones. Chain-extension of the external branches of the hyperbranched polystyrene is then achieved by living cationic polymerization of protected hydrophilic vinyl ethers. This yields polystyrene dendrigrafts surrounded by a dense poly(vinyl ether) shell that is made hydrophilic by deprotection of hydroxyl functions of vinyl ether units. The obtained nanometer-sized macromolecular structures are fully soluble in aqueous media and present unimodal and narrow size distribution with an average diameter of about 100 nm. The dimensions and shape of the individual macromolecules before and after the deprotection step were further investigate...

In recent years it has become clear that the future of polymer chemistry and of the polymer industry lies more in improving existing polymers rather than discovering new monomers. Thus, the focus has now turned towards the synthesis of either novel or better controlled architectures through “living” polymerization mechanisms.