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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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International audience

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...

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.

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...

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.

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.

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.

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.

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

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