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The action of various external stimuli on telechelic poly(ethylene oxide) bearing iron(III) tetraphenylporphyrin chloride or iron(II) tetraphenylporphyrin derivatives at their ends has been investigated in organic and water media. Fully reversible chain end coupling processes were shown to take place yielding bis-iron(III) μ-oxo-tetraphenylporphyrin poly(ethylene oxide) under changes in acido-basic conditions, solvent nature, or the action of redox additives. At low concentration macrocyclic poly(ethylene oxide)s of same molar mass as the linear poly(ethylene oxide) precursors are almost exclusively formed via intramolecular coupling whereas increasing the poly(ethylene oxide) concentration yields both intra- and intermolecular chain coupling and formation of large macrocycles with [bis-iron(III) μ-oxo-tetraphenylporphyrin poly(ethylene oxide)] repeating units. The mechanisms involved are discussed.

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...

Peripherally functionalized arborescent polystyrenes (PS) of various architectures and chain parameters (backbone DP n , number and DP n of branches, number of termini and functions) were prepared by covalently assembling different elementary building blocks of controlled DP n , synthesized using anionic and cationic polymerization techniques. These multifunctional dendritic macromolecules have narrow polydispersities (

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.

Polystyrene (PS) combs and dendrigrafts bearing di(hydroxymethyl) group termini at each branch end were used as starting materials for the preparation of branched and hyperbranched polymer structures with ferrocenyl moieties at their periphery. Quantitative acetalization of the 1,3-propanol ends using carboxaldehyde ferrocene yields polymers with one ferrocenyl moiety per branch terminus. By varying the size of the different macromolecular building blocks used in the preparation of the hyperbranched polymers, in particular the n of the PS blocks forming the external branches, a series of ferrocenyl-functionalized polystyrene combs and dendrigrafts was prepared. Their electrochemical properties were studied by cyclic voltammetry in organic solution and compared with the corresponding α-functional linear PS. Results show that all ferrocenyl groups in dendrigrafts are available and participate to the oxidation−reduction cycles while only a small fraction of the ferrocene groups is active in combs and linear PS.

Functional arborescent graft polystyrenes prepared by the graft-on-graft technique, involving the iterative grafting of end functional polymer chains onto reactive polymer backbones were synthesized. The zero-generation comb polymers and then the first generation hyperbranched structures were obtained by the coupling reaction of living α-acetal polystyryllithium onto linear or comb chains of poly(chloroethyl vinyl ether) (PCEVE) of controlled DP n and structure. Both the PS grafts and the PCEVE reactive backbones were synthesized individually by living polymerization techniques. Initiation of styrene polymerization from acetal functionalized lithium derivatives yield the co-functionalization of all external polystyrene branches. Derivatization of these acetal branch termini allowed the generation of aldehyde, hydroxyl and carboxyl groups as well as the introduction of functional organic molecules at the periphery of the nanoparticles.

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.

Highly branched starlike comb polystyrenes (star polymers with four and five arms constituted of PS combs) have been synthesized. The strategy developed is based on the highly selective coupling reaction of living polystyryllithium onto poly(chloroethyl vinyl ether) chains with a starlike chain architecture. The PS grafts and the poly(CEVE) building blocks were prepared individually by living polymerization techniques. The solution properties and the characteristic parameters ([η], Rg, Rh, ρ) of these new PS comb star macromolecules were determined and compared to those of the corresponding “linear” PS combs. The results confirm the much higher compactness of the new macromolecular structures, which behave as hard spheres in the whole molar mass domain examined.

The grafting of polystyryllithium onto chloroethyl ether functions of poly(chloroethyl vinyl ether) (PCEVE) chains is a selective reaction which allows the complete substitution of chloride of CEVE units by polystyrene (PS) chains. Since the PCEVE polymer backbone and the PS grafts can be prepared by living cationic and anionic polymerization, respectively, it is possible to synthesize PCEVE-g-PS polymers possessing both a backbone with controlled dimensions and an adjustable number of branches of precise length. This procedure was applied to the synthesis of a series of linear and macrocyclic comblike PCEVE-g-PS based on the use of linear and cyclic PCEVE as reactive backbone, respectively. The synthesis, the characterization and the solution properties of these linear and cyclic comblike polymers are reported.

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.

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.

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.

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.

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...

Macrocyclic polystyrenes prepared by a single-step, pseudo-unimolecular cyclization of a linear α-(diethoxyethyl)-ω-styrenylpolystyrene can effectively be analyzed by liquid chromatography at the critical point of adsorption. Using silica gel as the stationary phase and THF−hexane as the eluent, the macrocyclic oligomers are separated from their linear precursors and other nonfunctional linear oligomers. The quantitative determination of the cyclization yield can be carried out via appropriate detector calibration for the linears and cyclics. Additional information on the chemical structure of the linears and cyclics is obtained by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. In conclusion, a possible cyclization mechanism is given including an interpretation of the MALDI behavior of the samples.

A new strategy for the synthesis of vinyl type macrocyclic polymers of controlled molecular weight and molecular weight distribution has been investigated. It involves the direct coupling of an α-ω-heterodifunctional linear polymer precursor previously prepared by living polymerization. The cyclization is achieved under high dilution, by an appropriate activation of one of the polymer-ends in order to allow its reaction with the other end function. Its application to the preparation of polystyrenes and poly(vinyl ether)s with a macrocyclic structure, as well as ring closure mechanisms in the presence of different cyclization agents are reported.

The synthesis of bicyclic eight-shaped poly(chloroethyl vinyl ether)s of controlled molar masses and narrow polydispersities has been achieved in very good yield. The strategy used is derived from the one reported for the synthesis of monomacrocyclic poly(vinyl ether)s and polystyrene. The procedure consists in the preparation of a linear tetrafunctional precursor bearing two series of antagonist functions, namely, α,α'-distyrenyl-ω,ω'-diacetal-poly(CEVE). The synthesis and the characterization of this polymer by controlled living cationic polymerization of chloroethyl vinyl ether are first described. In a second step, performed in highly diluted conditions, the acetal ends of the precursor are selectively activated by an electrophilic catalyst in order to form carbocationic-like termini which rapidly add on the styrenyl function of the chain. The presence of two functions of each type on a poly(CEVE) chain allows the formation of two rings per chain. The structural investigation of the cyclized polymer by SEC and NMR supports that bicyclic eight-shaped poly(CEVE) can be prepared cleanly and almost quantitatively by this cyclization procedure based on unimolecular end-to-end coupling reactions

A new strategy for the synthesis of vinyl type macrocyclic polymers of controlled molecular weight and molecular weight distribution has been investigated. It involves the direct coupling of an α,ω-heterodifunctional linear polymer precursor previously prepared by living polymerization. The cyclization is achieved under high dilution, by appropriate activation of one of the polymer ends in order to allow its reaction with the other end function. The theoretical advantages of this approach compared to the conventional procedure involving the coupling of a living homodifunctional polymer precursor by a difunctional organic molecule are discussed

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.

A route to macrocyclic polymers based on a new unimolecular ring-closure process has been investigated. It involves the direct end-to-end coupling of an α,ω-bis[chloroiron(III) meso-tetraphenylporphyrin] telechelic linear polystyrene synthesized by living polymerization followed by chain-end functionalization. The corresponding macrocyclic polystyrene was obtained readily and selectively by intramolecular condensation of the α,ω-bis[chloroiron(III) meso-tetraphenylporphyrin] polymer ends in the presence of a base to yield a diiron(III)-μ-oxobis(porphyrin) dimer as ring-closing unit. Addition of dilute HCl was shown to rapidly reconvert the diiron(III)-μ-oxobis(porphyrin) unit into the initial bis[chloroiron(III) porphyrin], demonstrating the selectivity and complete reversibility of the cyclization process. The synthesis and detailed structural characterization of the α,ω-homodifunctional precursor and the corresponding macrocyclic polystyrene along with an analysis of the porphyrin dimerization reaction using NMR spectroscopy and size-exclusion chromatography coupled with a diode array detector are presented.

Macrotricyclic poly(vinyl ether)s of controlled molar masses and MWD are prepared by synthesizing in a first step a three-arm star-shaped poly(vinyl ether) from a diheterohexafunctional precursor by living cationic polymerization. The cyclization of each star arm is then achieved under highly diluted conditions by the promoted intramolecular addition of the active end groups onto the three remaining head functions. High cyclization yields are obtained without the detectable formation of polycondensates resulting from intermolecular reaction

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.

International audience

Preparation de polymere cyclique CH 3 CH(-OR 1 -)[CH 2 CH(OR)] n CH 2 CH(OR)CH 2 -R 1 (R=CH 2 CH 2 Cl, R 1 =-(CH 2 ) 4 OCH 2 PhCH(OMe)-) par polymerisation cationique vivante du chloroethyl vinyl ether amorcee par le systeme HI/ZnCl 2 /CH 2 =CHO(CH 2 ) 4 OCHW 2 PhCH=CH 2 puis cyclisation intramoleculaire

Two different methods of synthesis were examined for the preparation of poly(alkylvinylether)s with pendant 4′-cyano-4-oxy-biphenyl mesogenic groups attached to side chains of different length: a) anchoring of the mesogenic group onto an alkylvinylether monomer followed by polymerization or b) synthesis of the corresponding poly(chloroalkylvinylether)s and chemical substitution of the pendant chlorine by the mesogenic groups. Polymerization were performed with initiating systems based on activated iodide. Much better control of MW and MWD of the final polyvinylether chains was obtained when process b) was applied. Polymers with 2 and 4 carbons in the spacer do not show liquid crystalline properties. It is only with polymers having six carbon atoms in the spacer that mesophases were observed. Those issued from process b) give two distinct mesophases: a smectic A phase in the high temperature range and a smectic C phase for the low one. Polymers synthetized from process a) present only the smectic A phase. The effects of molecular weights and molecular weight distributions on the liquid crystalline properties have been examined and are discussed.

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.