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This work focuses on the temperature-dependent structural and rheological characterization of polystyrene- b-poly( n-butyl acrylate)- b-polystyrene triblock copolymers (PS- b-P nBA- b-PS) in the melt and, in particular, on their ability to show a lower disorder-to-order temperature (LDOT). To this aim, copolymers of varying block lengths, but keeping the P nBA block as a major component, were synthesized. Small-angle x-ray scattering revealed that the copolymers with short PS blocks (∼10 kg/mol) approach an LDOT but do not cross it. At room temperature, these copolymers exhibit higher moduli compared to a P nBA homopolymer due to the reinforcing effect of the PS but are flowing at temperatures above the glass transition of the PS. Increasing the PS and P nBA block length, to keep the same PS fraction, induces more profound changes in the structural and viscoelastic behaviors. Such a copolymer crosses the LDOT, leading to a microphase-separated and ordered state at high temperature. Contrary to the copolymers with short PS blocks, the flow regime was not reached, even at temperatures well above the glass transition of the PS. Instead, a low-frequency plateau was observed in rheology, showing the increased lifetime of the microphase-separated PS domains. ABA triblock copolymers exhibiting an LDOT behavior could, thus, be of interest for the design of thermoplastic elastomers or pressure-sensitive adhesives that can resist the flow at high temperatures.

We present a systematic experimental study of the shear rheology of metallosupramolecular assemblies based on entangled telechelic star polymers comprising one (single dynamic network) or two (double dynamics network) types of physical bonds with the aim to unravel the role of concentration and strength of these bonds on the nonlinear response. Model dynamic networks functionalized with terpyridine ligands were formed by adding different metal ions with increasing bonding strength, zinc, copper, and cobalt. The dynamics are driven by entanglement/disentanglement processes and a ligand exchange mechanism. Steady-state viscosities of single and double dynamics networks collapse onto a universal curve over a wide range of Weissenberg numbers based on terminal time (up to about 300 for single and 1000 for double), exhibiting stronger shear thinning (with an exponent of −0.76) compared to entangled neutral star polymers. Double dynamics networks consisting of two different metal ions (with different lifetimes) exhibit stronger mechanical coherence (rate-dependent fractional viscosity overshoot) and accumulate larger strain at steady-state flow compared to single-ion counterparts. The shear stress growth function signals exhibit weak, albeit unambiguous shear strain hardening, which becomes more pronounced for stronger associations. They also exhibit double overshoot, which reflects the interplay of association strength and chain deformation. Increasing the strength of associations leads to the failure of the Cox–Merz rule, which is more severe for single dynamic networks. The markedly different behavior of double dynamics networks is attributed to the fact that at sufficiently high ion content, the weaker bond acts as a sacrificial component, which provides local energy dissipation and enhances the overall deformability. This bears analogies with their linear viscoelastic response, which has revealed that the arm disentanglement (delayed due to the reversible bonds) effectively interpolates between the two single dynamic network components, depending on composition. Our results suggest ways to tailor the mechanical properties of this class of materials by judicious choice of the type and content of the ion.

Magneto-responsive nanocomposites are prepared by mixing 1–5 vol % of Fe nanoparticles (NPs) in a metallo-supramolecular network made of poly(n-butyl acrylate) (PnBA) bearing terpyridine side groups and cross-linked by the addition of different amounts of Zn2+ ions. To have a clear understanding of the stepwise increase of complexity, the thermomechanical behavior of these materials was characterized through shear linear rheology at each step of their preparation. The metallo-supramolecular networks reveal a clear transition from polymer- to network-driven dynamics when passing progressively from low (

We report on mechanically linked polymers containing a single catenane in the middle of the chain. These polymers were synthesized by a simple procedure consisting in “clicking” polymer chains onto a functionalized palladium-templated [2]catenane, allowing the preparation of a variety of mechanically linked polymers. The flexibility of the catenane junction was modulated by removing the Pd ion from the catenane to unlock the macrocycles and increase their mobility. We show that this mobility change has a strong impact on the solid-state properties of the polymers. This is illustrated by studying the glass transition temperature of polystyrene-based polymers and the crystallization behavior of poly(ethylene oxide)-based polymers. Our study proves that a change of flexibility of a single catenane inserted into a polymer chain drastically influences the polymer behavior in the solid state.

We report on the use of atomic force microscopy (AFM) to identify and characterize an intermediate state in macrocycle shuttling in a hydrogen bonded amide-based molecular shuttle. The [2]rotaxane consists of a benzylic amide macrocycle mechanically locked onto a thread that bears both fumaramide and succinic amide-ester sites, each of which can bind to the macrocycle through up to four intercomponent hydrogen bonds. Using AFM-based single-molecule force spectroscopy, we mechanically triggered the translocation of the ring between the two principal binding sites ("stations") on the axle. Equilibrium fluctuations reveal another interacting site involving the two oxygen atoms in the middle of the thread. We characterized the ring occupancy distribution over time, which confirms the intermediate in both shuttling directions. The study provides evidence of weak hydrogen bonds that are difficult to detect using other methods and shows how the composition of the thread can significantly influence the shuttling dynamics by slowing down the ring motion between the principal binding sites. More generally, the study illustrates the utility that single-molecule experiments, such as force spectroscopy, can offer for elucidating the structure and dynamics of synthetic molecular machines.

A series of tunable interpenetrating polymer network (IPN) hydrogels are designed by the orthogonal incorporation of two distinct types of reversible bonds, i.e., Schiff base bonds and metal–ligand...

We study the linear viscoelastic properties of polymeric networks formed by poly( n-butyl acrylate) telechelic stars end-capped with 2,2:6,2″-terpyridine (Star-PnBA-tpy4) and two types of metal-ligand cross-links with different lifetimes. The influence of interactions, mediated by temperature, nature of metal ions, and ion content, on the linear viscoelastic behavior of both single and double dynamics transient networks is systematically investigated by small amplitude oscillatory shear and creep rheometry. The experimental results reveal that the dynamics of networks with two different metal-ligand cross-links is much faster than expected, characterized by the average sticker lifetime rather than a discrete contribution of each metal-ligand complex. We model the dynamics with the help of our modified tube-based time marching algorithm by accounting for both association/dissociation dynamics of metal-ligand coordination and the entanglement dynamics. Two parameters are defined in the model, namely, the proportion of dangling ends and the average time during which a sticker is free. This allows us to quantify the transient dynamics of the network and, in particular, to determine how the sticker dynamics depend on temperature and ion content.

We investigate the viscoelastic properties of double dynamic networks (DDNs) based on side-functionalized P nBA chains. One of these networks is highly crosslinked by metal-ligand junctions characterized by a fast association/dissociation dynamics, while the other network is sparsely crosslinked with slow dynamic covalent networks (DCNs). We first show that modulating the dynamics of the metallosupramolecular networks, by playing with the temperature, the density of reversible junctions, or the stress applied, has direct consequences on the local equilibration of the DCN. The latter takes place by a constraint release Rouse process at the rhythm of the association/dissociation of the metal-ligand junctions. Then, based on creep-recovery experiments, we investigate the ability of the DDNs to recover their initial shape after a creep test and show again the important role played by the metallosupramolecular network. In particular, the sample recovery strongly depends on the network connectivity, which is enhanced if a denser metallosupramolecular network is used as it reduces the possible creep of the double dynamic network and increases its elastic memory. The sample recovery also depends on the association-dissociation dynamics of the metallosupramolecular bonds as it fixes how fast the stretched DCN can come back to its equilibrium conformation and can recover its initial shape after a large deformation has been applied. Adjusting the dynamics of the weak network is thus a key process to govern the viscoelastic response of the slow network.

Since the Industrial Revolution, technological advances have generated enormous emissions of various pollutants affecting all ecosystems. The detection and degradation of pollutants has therefore become a critical issue. More than 59 different remediation technologies have already been developed, such as biological remediation, and physicochemical and electrochemical methods. Among these techniques, advanced oxidation processes (AOPs) have been popularized in the treatment of wastewater. The use of ZnO as a photocatalyst for water remediation has been developing fast in recent years. In this work, the goals are to produce ZnO photocatalysts with different morphologies, by using a green sol-gel process, and to study both the influence of the synthesis parameters on the resulting morphology, and the influence of these different morphologies on the photocatalytic activity, for the degradation of an organic pollutant in water. Multiple morphologies were produced (nanotubes, nanorods, nanospheres), with the same crystalline phase (wurtzite). The most important parameter controlling the shape and size was found to be pH. The photoactivity study on a model of pollutant degradation shows that the resulting activity is mainly governed by the specific surface area of the material. A comparison with a commercial TiO2 photocatalyst (Evonik P25) showed that the best ZnO produced with this green process can reach similar photoactivity without a calcination step.

We report here a synthetic platform toward mono-functionalized tridentate macrocycles based on a pyridine-2,6-bis-carboxamide motif. These macrocycles bear a variety of functional groups at the fourth position of the pyridine, giving access to a wide range of synthetic methods for further derivatisation or preparation of more complex structures such as mechanically interlocked molecules or polymer materials. To illustrate the potential of this family of macrocycles a series of square planar palladium complex-based pseudorotaxanes, containing different axles and functional groups on the ring, are synthesised, and then used to prepare a macro-pseudorotaxane, i.e. a polymer containing a rotaxane junction, and mechanically-linked gels by a one-pot and a polyrotaxane approach.

We study the viscoelastic properties and the structure of a short hydrogenated polybutadiene (HPB) building block end-capped by terpyridine ligands. Adding metal ions in the sample leads to the formation of metallo-supramolecular junctions between the blocks, while the difference in polarity between the HPB chains and the metal complexes leads to the phase separation of the complexes into well-organized structures. By varying the nature and amount of metal ions added to the system, with the temperature, as well as with the sample thermal history, we show that it is possible to modulate these associations and obtain a very rich range of properties. In particular, while increasing the amount of metal ions leads to the sample reinforcement, it also causes a decrease of its melting temperature. This result is linked to the structure of the sample, which is characterized, in specific conditions, by the co-existence of two lamellar structures that we attribute to the existence of mono-complexes. The stability of these two lamellar structures is discussed based on the structural evolution during several heating and cooling ramps. We also show that the usually observed lamellar structure can be changed into a hexagonal structure if excess of metal ions are added to the sample.

The formation of micelles on surfaces by spin-coating dilute solutions of diblock, triblock, and tetrablock copoly(2-oxazoline)s in a non-selective solvent is demonstrated. The micelles are not preexistent in the initial solution but are formed during the evaporation of the solvent by precipitation of the least-soluble block. The morphology and size of the micelles vary according to the fraction of this block but are not dependent on the block order in the copolymer.

Non-covalent interactions are important for directing protein folding across multiple intermediates and can even provide access to multiple stable structures with different properties and functions. Herein, we describe an approach for mimicking this behavior in the self-assembly of metal-organic cages. Two ligands, the bend angles of which are controlled by non-covalent interactions and one ligand lacking the above-mentioned interactions, were synthesized and used for self-assembly with Pd

This work studies the linear viscoelastic properties of a series of low-dispersity poly(n-butyl acrylate) chains end-functionalized with 2,2′;6′,2″-terpyridine, able to self-associate by metal–ligand coordination. Depending on the architecture and functionality of the chains, the polymers self-assemble into different metallo-supramolecular bulk structures once metal ions are added. Linear building blocks (monofunctional or bifunctional) form longer chains while four-arm stars form networks. The properties of the obtained materials can be finely tuned depending on the length of the polymer chains and the type of metal. In this respect, enhanced control is gained over the dynamics of this class of metallo-supramolecular assemblies. Hence, they are extremely interesting for specific applications such as adhesives or mechanosensors.

The linear and nonlinear rheology of associative colloidal polymer assemblies with metallo-supramolecular interactions is herein studied. Polystyrene-b-poly(tert-butylacrylate) with a terpyridine ligand at the end of the acrylate block is self-assembled into micelles in ethanol, a selective solvent for the latter block, and supramolecularly connected by complexation to divalent metal ions. The dependence of the system elasticity on polymer concentration can be semi-quantitatively understood by a geometrical packing model. For strongly associated (Ni2+, Fe2+) and sufficiently concentrated systems (15 w/v%), any given ligand end-group has a virtually 100% probability of being located in an overlapping hairy region between two micelles. By assuming a 50% probability of intermicellar crosslinks being formed, an excellent prediction of the plateau modulus was achieved and compared with the experimental results. For strongly associated but somewhat more dilute systems (12 w/v%) that still have significant overlap between hairy regions, the experimental modulus was lower than the predicted value, as the effective number of crosslinkers was further reduced along with possible density heterogeneities. The reversible destruction of the network by shear forces can be observed from the strain dependence of the storage and loss moduli. The storage moduli of the Ni2+ and Zn2+ systems at a lower concentration (12 w/v%) showed a rarely observed feature (i.e., a peak at the transition from linear to nonlinear regime). This peak disappeared at a higher concentration (15 w/v%). This behavior can be rationalized based on concentration-dependent network stretchability.

This work reviews an eco-friendly process for producing TiO2 via colloidal aqueous sol–gel synthesis, resulting in crystalline materials without a calcination step. Three types of colloidal aqueous TiO2 are reviewed: the as-synthesized type obtained directly after synthesis, without any specific treatment; the calcined, obtained after a subsequent calcination step; and the hydrothermal, obtained after a specific autoclave treatment. This eco-friendly process is based on the hydrolysis of a Ti precursor in excess of water, followed by the peptization of the precipitated TiO2. Compared to classical TiO2 synthesis, this method results in crystalline TiO2 nanoparticles without any thermal treatment and uses only small amounts of organic chemicals. Depending on the synthesis parameters, the three crystalline phases of TiO2 (anatase, brookite, and rutile) can be obtained. The morphology of the nanoparticles can also be tailored by the synthesis parameters. The most important parameter is the peptizing agent. Indeed, depending on its acidic or basic character and also on its amount, it can modulate the crystallinity and morphology of TiO2. Colloidal aqueous TiO2 photocatalysts are mainly being used in various photocatalytic reactions for organic pollutant degradation. The as-synthesized materials seem to have equivalent photocatalytic efficiency to the photocatalysts post-treated with thermal treatments and the commercial Evonik Aeroxide P25, which is produced by a high-temperature process. Indeed, as-prepared, the TiO2 photocatalysts present a high specific surface area and crystalline phases. Emerging applications are also referenced, such as elaborating catalysts for fuel cells, nanocomposite drug delivery systems, or the inkjet printing of microstructures. Only a few works have explored these new properties, giving a lot of potential avenues for studying this eco-friendly TiO2 synthesis method for innovative implementations.

A standard method of protein immobilization is proposed, based on the use of protein-polyelectrolyte complexes (PPCs) as building blocks for layer-by-layer assembly. Thicker multilayers, with a higher polyelectrolyte fraction, are obtained with PPCs compared to single protein molecules. Biological activity is not only maintained, but specific activity is also higher, as demonstrated for lysozyme-poly(styrene sulfonate) complexes. This is attributed to the more hydrated state of the assemblies. This new method of protein immobilization opens up perspectives for biotechnology and biomedical applications.

Stimuli-responsive double hydrophilic diblock copolymers have been prepared that consist of poly(N-isopropylacrylamide)-block-poly(2-(dimethylamino)ethyl methacrylate) sequences terminated by a terpyridine ligand. These building blocks are assembled in aqueous media in a stepwise manner, by first forming metallo-supramolecular ABA triblock copolymers and then gels by thermo-induced micellar aggregation. This study sheds light on the subtle interplay that exists between the responsive behaviour of the core and corona forming blocks. Due to the intrinsic sensitivity of the constituting polymer chains and the non-covalent interactions between them, supramolecular gels respond to specific external triggers. These stimuli allow the manipulation of numerous rheological aspects of the assembled materials, including network formation and dynamics. Interestingly, an independent control over the network formation and dynamics is notably achieved via an appropriate choice of the metal ions and of the length of the associating block. By playing with the architecture of the associating copolymers and the nature of the metal ions, this work further demonstrates the possibility to build materials possessing either a mono or dual relaxation mechanism via a unique approach.

A new photo-sensitive diblock copolymer composed of a hydrophilic sequence of poly(ethylene oxide) (PEO) linked to a CO2-philic sequence of poly(1H,1H,2H,2H-heptadecafluorodecyl acrylate) (PFDA) by a light sensitive o-nitrobenzyl group was successfully synthesized by RAFT polymerization and used as a stabilizer for the free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) dispersion in α,α,α-trifluorotoluene and supercritical carbon dioxide (scCO2). Thanks to this fluorinated stabilizer, well-defined particles of PHEMA down to 350 nm diameter were produced in scCO2. Advantageously, the photocleavable group at the block junction of the stabilizer could be cleaved by exposing the particles to UV light so that the fluorinated block could be extracted in TFT or scCO2. As supported by X-ray photoelectron spectroscopy (XPS) analysis, up to 80% of the fluorinated block of the stabilizer can be removed, leading to efficient swelling and dispersion of the resulting PHEMA nanogels in water.

One of the first examples of supramolecular gels presenting independent dual dynamics is built through a combination of hydrophobic and metal-ligand interactions. The associating building block consists in a water-soluble linear polymer terminated by a short hydrophobic sticker at one end, and a coordinating moiety at the other end. The distinct supramolecular nature of these noninterfering binding motifs allows the dynamics of the hydrogels to be finely tuned in an orthogonal fashion by the application of specific stimuli. Precisely, the solvent-induced plasticization of the hydrophobic associations and the acid-promoted dissociation of the metal-ligand complexes are used to control the network dynamics. By opposition to classically encountered binary gel-sol responses, we demonstrate that the stimuli-induced transition in material properties can be gradual, provided that the material structure is well designed and strong enough.

The dynamics of supramolecular networks made up of partially hydrolyzed poly(n-butyl acrylate) [PnBA] is investigated. These linear entangled random copolymers [PnBA-AA] self-assemble via hydrogen bonding interactions between carboxylic acid groups. Two types of supramolecular assemblies are revealed, i.e., binary assembly of carboxylic acid dimers and collective assembly of dimers into distinct poly(acrylic acid) [PAA] domains. The latter is proved by emergence of new relaxation processes in broadband dielectric spectroscopy while the former is evident by an increase of the glass transition temperature as well as retardation of segmental mobility observed by rheology. Therefore, a “sea–island” morphology containing geometrically confined PAA nanodomains embedded in a PnBA-rich matrix is suggested for the supramolecular network. Thermodynamic theories are employed to rationalize the existence of an interlayer with restricted mobility between the two phases. A fraction of PnBA-AA segments that are trapped ...

“Smart” materials have considerably evolved over the last few years for specific applications. They rely on intelligent macromolecules or (supra-)molecular motifs to adapt their structure and properties in response to external triggers. Here, a supramolecular stimuli-responsive polymer gel is constructed from heterotelechelic double hydrophilic block copolymers that incorporate thermo-responsive sequences. These macromolecular building units are synthesized via a three-step controlled radical copolymerization and then hierarchically assembled to yield coordination micellar hydrogels. The dynamic mechanical properties of this particular class of materials are studied in shear flow and finely tuned via temperature changes. Notably, rheological experiments show that structurally reinforcing the micellar network nodes leads to precise tuning of the viscoelastic response and yield behavior of the material. Hence, they constitute promising candidates for specific applications, such as mechano-sensors.

This Review highlights the large number of methods to exploit colloidal assembly of comparably simple particles with nano- to micrometer dimensions in order to access complex structural hierarchies from nanoscopic over microscopic to macroscopic dimensions

The effect of poly(ethylene oxide) [PEO]−metal salt complexation on the dynamics and microstructure of PEO−nickel chloride [NiCl2] systems is investigated by rheology and X-ray scattering. Annealed PEO−nickel salt systems exhibit network properties above the melting temperature of PEO, characterized by a second elastic plateau, beyond the reptation time of PEO chains. The level of the second plateau strongly depends on the annealing conditions and the ion content. In PEO−NiCl2 networks, the linear viscoelastic region is experimentally out of reach, meaning that their viscoelastic properties strongly depend on strain and strain rate as well as any deformation history. The network can be broken down by large-amplitude shear and reversibly reformed under quiescent conditions. X-ray scattering reveals formation of distinct crystalline structures of PEO−NiCl2 complexes, which are different from those of both neat PEO and nickel salt. The combined rheology and X-ray scattering results indicate that the network results from a small fraction of trapped PEO chains, which are bridging the crystalline domains of PEO−NiCl2 complexes

The melt dynamics of poly(ethylene oxide) [PEO]–nickel chloride [NiCl2] systems are analyzed by proton NMR relaxometry and rheology. A consistent picture of the corresponding microstructure is proposed based on the combined results. Rheology reveals the presence of a weak gel due to PEO–metallic salt complexation, evidenced by a low second storage modulus plateau (

Background Osmosis drives transcapillary ultrafiltration and water removal in patients treated with peritoneal dialysis. Crystalloid osmosis, typically induced by glucose, relies on dialysate tonicity and occurs through endothelial aquaporin-1 water channels and interendothelial clefts. In contrast, the mechanisms mediating water flow driven by colloidal agents, such as icodextrin, and combinations of osmotic agents have not been evaluated. Methods We used experimental models of peritoneal dialysis in mouse and biophysical studies combined with mathematical modeling to evaluate the mechanisms of colloid versus crystalloid osmosis across the peritoneal membrane and to investigate the pathways mediating water flow generated by the glucose polymer icodextrin. Results In silico modeling and in vivo studies showed that deletion of aquaporin-1 did not influence osmotic water transport induced by icodextrin but did affect that induced by crystalloid agents. Water flow induced by icodextrin was dependent upon the presence of large, colloidal fractions, with a reflection coefficient close to unity, a low diffusion capacity, and a minimal effect on dialysate osmolality. Combining crystalloid and colloid osmotic agents in the same dialysis solution strikingly enhanced water and sodium transport across the peritoneal membrane, improving ultrafiltration efficiency over that obtained with either type of agent alone. Conclusions These data cast light on the molecular mechanisms involved in colloid versus crystalloid osmosis and characterize novel osmotic agents. Dialysis solutions combining crystalloid and colloid particles may help restore fluid balance in patients treated with peritoneal dialysis.

The thermally-induced gelation and gel properties of concentrated aqueous solutions of double thermoresponsive poly(N-vinylamide)-based di- and triblock copolymers are studied by rheology. The copolymers under investigation, prepared by cobalt-mediated radical polymerization and coupling reactions, are composed of poly(vinylcaprolactam) (PNVCL) blocks and of a statistical poly(vinylcaprolactam-stat-vinylpyrrolidone) segment with a cloud point temperature (TCP) higher than that of PNVCL. Heating the di- and triblock solutions beyond the first phase transition temperature favors gel formation while heating above the second TCP leads to opaque gels without macroscopic demixing. Moduli of the triblock hydrogels are systematically higher than those of the corresponding diblocks, even above the second transition. Rheological data suggest distinct micellar structures for each copolymer architecture: densely packed micelles of diblocks and 3-D networks of bridged micelles for triblocks. Strain sweep experiments also emphasize the positive effect of the micelle bridging on the elasticity and stability of the hydrogels. The formation and properties of the obtained gels are also shown to depend on the copolymer concentration, block length, and composition. Addition of salt also allows us to tune the phase transition temperatures of these double thermoresponsive hydrogels. © 2015 The Royal Society of Chemistry.

International audience; Localization of the photosensitizer conjugation site in amphiphilic block copolymers is shown to have a great impact on photodynamic therapy efficiency. To this end, an asymmetric multifunctional derivative of the azadipyrromethene boron difluoride chelate (aza-BODIPY) was synthesized and inserted at specific locations in polypeptide-based rod-coil amphiphilic block copolymers. A study of the photophysical properties of the vesicle nanocarriers, obtained by self-assembly of these copolymers, as well as in vitro tests on two cancer cell lines were performed. This study aims at providing guidelines for the optimization of the synthetic design of therapeutic nanomedicines with minimal amounts of photosensitive molecules.

At the basis of smart self-assembled materials are lying small building blocks that can hierarchically assemble in response to stimuli, e.g., temperature or chemical species. In this context, the synthesis of terpyridine end-capped poly(2-(dimethylamino)ethyl methacrylate)-block-poly(N-isopropylacrylamide) diblock copolymers via controlled radical copolymerization is reported here. The self-assembly of those copolymers is investigated in dilute aqueous solutions while varying temperature or adding transition metal ions, respectively, leading to the formation of micellar nanostructures or metallosupramolecular triblock copolymers.

A poly(methyl methacrylate)-block-poly(4-vinylpyridine)-block-polystyrene (PMMA-b-P4VP-b-PS) triblock terpolymer is synthesized by ATRP to study its self-assembly with PAA in organic solvents. The self-assembly behavior of this system is compared with the one of a mixture of two diblocks, namely polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and poly(methyl methacrylate)-block-poly(methacrylic acid) (PMMA-b-PMAA). For both systems, formation of hydrogen-bonded complexes between the P4VP and PMAA or PAA blocks occurs. These complexes become insoluble in the solvent used and micelles with a P4VP/P(M)AA complexes core surrounded by PS and PMMA coronal chains are obtained in both cases. These micelles are analyzed by DLS and TEM. Spherical micelles are formed for both systems but the hydrodynamic radii obtained for the two types of micelles are different. Indeed, the micelles formed by the PMMA-b-P4VP-b-PS + PAA system are smaller than those observed for the PS-b-P4VP + PMMA-b-PMAA system. Finally, the effect of the molar ratio of the P4VP/PMAA complexing blocks is investigated.

Associating polymers constitute a fascinating class of materials because of the richness in their rheological behaviors. They may find application in numerous areas, provided that their mechanical properties can be tailored to fulfill specific requirements. In this context, this study aims to control the magnitude of the viscoelastic response of coordination micellar hydrogels built through the hierarchical assembly of heterotelechelic poly(N-isopropylacrylamide). The influence of different variables on the rheological properties of those materials is investigated and discussed in term of cross-linking density. In this respect, two distinct regimes are distinguished that correspond to the well percolated network, with a high cross-linking density, and the weakly percolated network, with a low cross-linking density.

Amphiphilic diblock copolythiophenes are synthesized by an efficient two-step synthetic strategy. The block architecture is created via the quasi-living Grignard metathesis reaction, after which ionic imidazolium moieties are introduced by substitution on the bromohexyl side chains of one of the monomer constituents. The compositional influence on the solution behavior and thermal properties of both the precursor and ionic block copolythiophenes is investigated. The novel materials are of particular appeal for integration in organic solar cell stacks, either as active layer or interlayer materials.

The light-induced formation of pH and temperature-responsive poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) nanocages is demonstrated here. The strategy is based on the self-assembly in aqueous solutions of a photocleavable poly(tert-butyl acrylate)-hv-poly[2-(dimethylamino)ethyl methacrylate] block copolymer (PtBA-hv-PDMAEMA, where -hv- is the photocleavable junction) into spherical micelles, followed by first PDMAEMA cross-linking by a bis-iodo compound and then by UV light irradiation. The exposure to light induces the cleavage of the junction between the PtBA core and the cross-linked PDMAEMA shell of the micelles. The PtBA block is then extracted to obtain the desired nanocages. The size change of the nanocages in response to pH and temperature is investigated by dynamic light scattering. Finally, the ability to functionalize the internal cavity of the nanocages is demonstrated.

Associating polymers constitute a fascinating class of materials because of the richness in their rheological behavior. Their rheology is mainly dictated by the nature and intrinsic stabilities of the transient associations. Here, we report on the combination of hydrophobic interaction and coordinative bonds through the synthesis of heterotelechelic water-soluble polymers. The characteristics of supramolecular cross-links allow the construction of mechano-responsive hydrogels showing an outstanding “two-step” gel-to-sol transition. Contributions of both supramolecular cross-links are investigated by rotational rheometry while varying the hydrophobic segment length and the type of metal. In this respect, an unprecedented control is gained over the response of multicomponent networks.

A series of ionic polythiophenes, in homopolymer and random copolymer configurations, is prepared via the Grignard metathesis (GRIM) polymerization protocol and subsequent substitution on the bromohexyl side chains with N-methylimidazole. The introduced structural variations - comonomer ratio, side chain composition, counter ions - allow tuning of the thermal properties and solution behavior of the resulting conjugated polymers. As expected, the solubility depends majorly on the number of ionic groups and the counter ions. The most peculiar behavior is observed for the P3HT-P3(MIM)HT-Br 50/50 random copolymer, which shows organization of the polymer chains in solution and thin film dependent on the preparation conditions. Dynamic light scattering studies confirm that the ordered solid-state structure is somewhat maintained when the copolymer is dissolved in a bad solvent mixture. The ionic (co)polythiophenes are generally more resistant to thermal degradation than their precursors. The precursor polymers all show a clear semi-crystalline behavior, with a decrease in crystallinity upon decreasing the number of regular 3-hexylthiophene units. On the other hand, the studied ionic (co)polythiophenes are fully amorphous. Changes in the counter ions have dramatic effects on the thermal properties. Bromine counter ions render the polymers strongly hygroscopic. The novel materials are of particular appeal in the field of organic photovoltaics, in which the imidazolium-substituted (co)polythiophenes can be beneficially applied as constituents of either active layers or electron transport layers. Their processability from green solvents is also of major importance for the field. © 2013 Elsevier Ltd. All rights reserved.

Synthesis of combs with well-entangled backbones and long branches with high densities has always been a challenge. Steric hindrance frequently leads to coupling of chains and structural imperfections that cannot be easily distinguished by traditional characterization methods. Research studies have therefore tried to use a combination of different methods to obtain more information on the actual microstructures. In this work, a grafting-from approach is used to synthesize poly(n-butyl acrylate) combs using atom transfer radical polymerization (ATRP) in three steps including the synthesis of a backbone, cleavage of protecting groups and growth of side branches. We have compared the linear viscoelastic properties theoretically predicted by a time marching algorithm (TMA) tube based model with the measured rheological behaviour to provide a better insight into the actual microstructure formed during synthesis. For combs with branches smaller than an entanglement, no discernible hierarchical relaxation can be distinguished, while for those with longer branches, a high frequency plateau made by entangled branches can be separated from backbone's relaxation. Dilution of the backbone, after relaxation of side branches, may accelerate the final relaxation, while extra friction can delay it especially for longer branches. Such a comparison provides a better assessment of the microstructure formed in combs.

This work focuses on the linear viscoelastic properties of entangled telechelic bulk metallo-supramolecular polymers. The latter are based on linear and star poly(n-butyl acrylate)s functionalized with a terpyridine ligand at each chain extremity, in the presence of transition metal ion of varying nature. The systems are investigated both experimentally and theoretically using small amplitude oscillatory shear and a modified version of the tube-based time marching algorithm (TMA), respectively. The experimental data reveal that sample relaxation depends on both disentanglement and association dynamics, with the respective importance of these two processes depending on the nature of the metal ion and on the temperature. A good description of the data is achieved using the modified TMA model, provided that dissociation events of metal-ligand complexes occur via ligand exchange. The model contains two fitting parameters, i.e., the fraction of unassociated stickers and the longest time needed in order to ensure that all the chains were dissociated at least once. This latter time is found to be independent of the chain architecture and is well described by an Arrhenius equation, which allows the derivation of the related activation energy. This work provides the necessary framework to explore other metallo-supramolecular networks, built from different chain architectures, and exploit the large richness of their dynamics.

Aqueous solutions of terpyridine end-functionalized Pluronics are investigated with or without the addition of Ni 2+ and Zn 2+ ions. Thermorheological measurements on these solutions show in some cases temperature-dependent sol-gel transitions. Without added metal ions, the thermorheological behavior is controlled by the composition of the Pluronics and the presence of clustered terpyridines. With added metal ions, the thermorheological behavior is essentially controlled by the terpyridine metal ion complexes. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

This contribution describes the synthesis and associating behavior in water of a multiresponsive amphiphilic diblock copolymer. This copolymer is composed of an hydrophobic photocleavable poly(para-methoxyphenacyl methacrylate) block (PMPMA) and a hydrophilic thermosensitive poly[(oligo ethylene glycol)methacrylate] block (POEGMA). The PMPMA-b-POEGMA copolymer forms micelles with a PMPMA core and a POEGMA corona in water. Light irradiation leads to the transformation of PMPMA into poly(methacrylic acid) (PMAA) and to the disruption of the initial micelles. The response of the accordingly obtained PMAA-b-POEGMA copolymer to pH, temperature, calcium (Ca2+), and phosphate (PO 4 3-) ions is demonstrated. © 2012 American Chemical Society.

A polystyrene-[Ni 2+]-poly(ethylene oxide) metallo-supramolecular block copolymer (PS-[Ni 2+]-PEO), where -[ is a terpyridine, is used to create nanoporous thin films with free terpyridine ligands homogenously distributed on the pore walls. The PS-[Ni 2+]-PEO block copolymer is synthesized by a two step assembly process, and is then self-assembled into a thin film in order to obtain PEO cylinders oriented perpendicularly to the film surface. The supramolecular junction is opened by exposing the film to an excess of a competing ligand, and the free PEO block is then rinsed away by a selective solvent. The presence of the terpyridines on the pore walls is evidenced by fluorescence spectroscopy after formation of a fluorescent complex with an europium salt. © 2012 American Chemical Society.

A polystyrene- block -poly(ethylene oxide) block copolymer bearing a photocleavable junction between the blocks is used to form nanoporous thin fi lms with carboxylic acid functions homogeneously distributed on the pore walls. The presence of the carboxylic acid groups is evidenced by fl uorescence spectroscopy after their reaction with a diazomethane functionalized fluorescent dye. In addition, the initial light-responsivethin film, acting as a photoresist, can be easily patterned to selectively generate porosity in predetermined areas. In that way, fluorescent patterns can be obtained as evidenced by fluorescent microscopy.

We just clicked: A convergent approach consisting of two successive copper(I)-catalyzed azide-alkyne cycloaddition "click" reactions leads to a diblock copolymer in which the two blocks are linked by a rotaxane-type mechanical bond (see scheme). Rotaxane formation is templated by a square-planar PdII complex. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Graft copolymers have been prepared by one-step organometallic-mediated radical polymerization (OMRP) for the first time. Poly(ethylene glycol) acrylate (PEGA) was copolymerized with vinyl acetate (VAc) to yield well-defined P(PEGA-grad-VAc) gradient graft copolymers using bis(acetylacetonato)cobalt(II) as the control agent. The influence of experimental parameters such as the PEGA/VAc molar ratio, the nature of the initiator, and the temperature on the control of the copolymerization was discussed. The use of an excess of cobalt complex appeared as a key parameter to maintain a good level of control when higher contents of acrylate were used in the comonomer feed. The reactivity ratios were estimated and revealed that PEGA was added around 30 times faster than VAc, which gave access to a gradient P(PEGA-grad-VAc) copolymer or to a P(PEGA-grad-VAc)-b-PVAc diblock copolymer when the VAc polymerization was pursued after the full consumption of PEGA. The amphiphilic character of the copolymers makes them prone to self-assemble into micelles in water, as evidenced by dynamic light scattering.

The light-responsive behavior in solution and in thin films of block copolymers bearing 2-nitrobenzyl photocleavable esters as side groups is discussed in this article. The polymers were synthesized by grafting 2-nitrobenzyl moieties onto poly(acrylic acid)-block-polystyrene (PAA-b-PS) precursor polymers, leading to poly(2-nitrobenzyl acrylate-random-acrylic acid)-block-polystyrene (P(NBA-r-AA)-b-PS) block copolymers. The UV irradiation of the block copolymers in a selective solvent for PS led to the formation of micelles that were used to trap hydrophilic molecules inside their core (light-induced encapsulation). In addition, thin films consisting of light-responsive P(NBA-r-AA) cylinders surrounded by a PS matrix were achieved by the self-assembly of P(NBA-r-AA)-b-PS copolymers onto silicon substrates. Exposing these films to UV irradiation generates nanostructured materials containing carboxylic acids inside the cylindrical nanodomains. The availability of these chemical functions was demonstrated by reacting them with a functional fluorescent dye. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 Light-responsive poly(2-nitrobenzyl acrylate-random-acrylic acid)-block-polystyrene (P(NBA-r-AA)-b-PS) block copolymers (P(NBA-r-AA)-b-PS) have been synthesized and further self-assembled in solution as well as in thin films. In solution, the block copolymers were used to encapsulate hydrophilic molecules inside the core of light-induced micelles. In addition, light-responsive nanostructured thin films have been prepared onto silicon substrates. Exposing these films to UV irradiation generates chemical functionalities inside the photo-responsive nanodomains. Copyright © 2011 Wiley Periodicals, Inc.

Bis(terpyridine) and metallo-bis(terpyridine) Pluronics have been synthesized starting from commercially available P105 and P123 hydroxytelechelic Pluronics. The grafting of terpyridine ligands at the extremity of the Pluronic chains results in the further association of the Pluronic micelles in water. Increasing temperature decreases the solubility of the Pluronics, but also increases the solubility of the terpyridine groups. The addition of 0.5 equiv. nickel(II) ions compared to terpyridine groups induces the formation of bis(terpyridine) nickel(II) complexes and disrupts the initial hydrophobic terpyridine aggregates. In that case, formation of flower-like micelles in which the coronal chains form loops due to the terpyridine nickel(II) complexes is observed in the dilute regime.

We report on the self-assembling behavior in thin films of mixtures of polystyrene-block-poly(ethylene oxide) copolymers (PS-b-PEO), having PEO cylindrical microdomains, with poly(acrylic acid) homopolymers (PAA). We study the effect of adding PAA of different molecular weights, specifically interacting with the PEO block by hydrogen bonding, on the thin film characteristics: morphology, microdomain orientation and spacing. It is found that the addition of PAA induces an orientation of the cylindrical microdomains perpendicularly to the film surface. The lattice spacing increases with the amount of PAA added until a transition toward lamellar morphology is observed. This transition occurs at lower PAA content for PAA of small molecular weight. The experiments also reveal that the PAA homopolymer is localized in the center of the PEO microdomains. The trends observed in the experiments were validated by self-consistent field theory calculations using a newly and specifically developed model.

We report on the micellization behavior of tri- and tetrablock copoly(2-oxazoline)s in water-ethanol mixtures. The copolymers are based on different combinations of 2-methyl-, 2-ethyl-, 2-phenyl-, and 2-nonyl-2-oxazoline. The solvophilic/solvophobic balance of these copolymers can be tuned thanks to the solubility dependence of the poly(2-phenyl-2-oxazoline) block on the solvent composition. Characterization of the obtained micelles by dynamic light scattering and transmission electron microscopy revealed that their size and morphology depend on the solvophobic content of the copolymers and on the block order. Spherical micelles are always obtained when poly(2-nonyl-2-oxazoline) is the only solvophobic block. When the solvophobic fraction consists of both the poly(2-phenyl-2oxazoline) and poly(2-nonyl-2-oxazoline) blocks, spherical and cylindrical micelles as well as vesicles have been observed. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3095-3102, 2010

The self-assembly of amphiphilic diblock copolymers in block selective solvents is well documented in the scientific literature. It gives rise to micelles in which the insoluble blocks form a core, which is surrounded by a corona that contains the soluble blocks. Another method to trigger micellization consists in introducing additional non-covalent interactions such as electrostatic interactions or hydrogen bonding in an initially soluble block copolymer. The non-covalent complexes that result from these interactions should be insoluble in order to induce micellization. Such insoluble complexes can be generated by mixing, in a non-selective solvent for all the individual blocks, two block copolymers or a block copolymer and a homopolymer, that contain mutually interacting blocks. This mixing process may, therefore, lead to insoluble non-covalent complexes, which further aggregate into micellar cores stabilized by the uncomplexed blocks. Such a strategy has been successfully implemented in both aqueous and non-aqueous solvents to create interesting stimuli-responsive systems, mainly using ionic interactions and hydrogen bonding. This feature article will summarize these approaches.