Clément Mugemana

Connecting micelles by metallo-supramolecular interactions : towards stimuli responsive hierarchical materials

A novel strategy to link block copolymer micelles via metal–ligand interactions, leading to hierarchical supramolecular networks is presented. The mechanical properties of the obtained materials can be tuned easily by the choice of the metal ions used. The strong networks exhibit a chemical and mechanical stimuli responsive behavior, with almost instantaneous recovery in the latter case.

Tuning block copolymer micelles by metal–ligand interactions

A terpyridine end-capped poly(styrene)-block-poly(tert-butylacrylate) (PS-b-PtBA-[) copolymer has been synthesized by nitroxide-mediated radical polymerization using a terpyridine-functionalized initiator. Micellization of this copolymer was achieved in ethanol, a selective solvent for the PtBA block. The formed micelles consist of a PS core and a PtBA corona. Terpyridine ligands are located at the extremity of the PtBA chains and are available for complexation with metal ions. The effect of the addition of various metal ions to this system was studied in the dilute regime by dynamic light scattering. Whenever the concentration of the micelles is sufficiently low, addition of metal ions only results in the intramicellar complexation of terpyridine-ended PtBA coronal chains. Since terpyridine can either form mono-complexes or bis-complexes with metal ions, different situations have been observed depending on the metal-to-ligand ratio and on the nature of the metal ions. Finally, the possibility to use these metal–ligand complexes to add an additional poly(ethylene oxide) layer on the initial micelles has been demonstrated. This new approach opens a pathway to tune the size, conformation and functionality of coronal chains in block copolymer micelles.

Pore‐Functionalized Nanoporous Materials Derived from Block Copolymers

This review deals with nanoporous materials made from the self-assembly of block copolymers with a special interest in the chemical functions covering the surface of their nanopores. A detailed overview of the existing methods and strategies to generate well-defined organic functional groups covering the surface of the pore walls is provided. This further enables to finely tune the affinity of the pore walls and to perform well-defined chemical reactions onto them, which is essential for further dedicated applications.

Functionalized nanoporous thin films from metallo-supramolecular diblock copolymers

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.

Tuning micellar morphology and rheological behaviour of metallo-supramolecular micellar gels

Well-defined polystyrene-block-poly(tert-butylacrylate) diblock copolymers end-functionalized by a terpyridine ligand (PS-b-PtBA-[) were synthesized by nitroxide mediated polymerization (NMP) in the presence of an initiator bearing a terpyridine moiety. These materials were then hierarchically organized over two levels of self-assembly to yield metallo-supramolecular micellar gels. The first level of self-assembly is the formation of micelles in the dilute regime. Spherical or cylindrical micelles were obtained depending on the block copolymer composition as well as the method of preparation. The second level of self-assembly was triggered upon addition of Ni(II) ions to the concentrated micellar solutions. Rotational rheometry was used to probe the impact of the micellar morphology and the presence of a co-solvent on the mechanical properties of the gel.

Metallo-supramolecular block copolymer micelles: recent achievements

In this Highlight, we focus on micellar structures obtained from metallo-supramolecular block copolymers. Two different systems are discussed: those in which metal–ligand complexes are located at the core/corona interface and those bearing metal–ligand complexes at the extremity of their coronal chains. The different nanostructures obtained so far as well as the possible applications of those systems are briefly discussed.

Palladium N-Heterocyclic Carbene Precatalyst Site Isolated in the Core of a Star Polymer.

An approach for supporting a Pd-NHC complex on a soluble star polymer with nanoscale dimensions is described. The resulting star polymer catalyst exhibits excellent activity in cross-coupling reactions, is stable in air and moisture, and is easily recoverable and recyclable. These properties are distinct and unattainable with the small-molecule version of the same catalyst.

Ring Opening Metathesis Polymerization of Cyclopentene Using a Ruthenium Catalyst Confined by a Branched Polymer Architecture

Multi-arm polystyrene stars functionalized with Grubbs-type catalysts in their cores were synthesized and used for the ring-opening metathesis polymerization (ROMP) of cyclopentene. The spatial confinement of the catalytic sites and the nanoscale phase separation between polystyrene and the growing polypentenamer chains lead to a dramatic inhibition of the ROMP termination and chain transfer steps. Consequently, cyclopentene polymerizations proceeded fast and with a high degree of conversion even in air. The Grubbs second generation catalyst was oxidatively inactivated under the same conditions. In contrast to conventional small-molecule catalysts, the ultimate degree of conversion of the cyclopentene monomer and the polydispersity of the product polypentenamer are not affected by the temperature. This indicates that spatial confinement of the catalyst results in a significant change in the activation parameters for the alkene metathesis ring-opening.