Functionalized nanoporous thin films from metallo-supramolecular diblock copolymers

Diblock and Triblock Copolymers as Nanostructured Precursors to Functional Nanoporous Materials: From Design to Application

Block copolymers have gained tremendous interest from the scientific community in the last two decades. These macromolecular architectures indeed constitute ideal nanostructured precursors for the generation of nanoporous materials meant for various high added value applications. The parallel emergence of controlled polymerization techniques has notably enabled to finely control their molecular features to confer them with unique structural and physicochemical properties, such as low dispersity values (Đ), well-defined volume fractions, and controlled functionality. The nanostructuration and ordering of diblock or triblock copolymers, which can be achieved through various experimental techniques, including channel die processing, solvent vapor or thermal annealing, nonsolvent-induced phase separation or concomitant self-assembly, and nonsolvent-induced phase separation, allows for the preparation of orientated microphase-separated copolymers whose morphology is dictated by three main factors, i.e., Flory-Huggins interaction parameter between constitutive blocks, volume fraction of the blocks, and polymerization degree. This review article provides an overview of the actual state of the art regarding the preparation of functional nanoporous materials from either diblock or triblock copolymers. It will also highlight the major applications of such peculiar materials.

Towards Macroscopically Anisotropic Functionality: Oriented Metallo-supramolecular Polymeric Materials Induced by Magnetic Fields

Based on the predesigned self-selective complexation, metallo-supramolecular P3HT-b-PEO diblock copolymers with varying block ratios were synthesized, and their oriented polymer films generated during solvent evaporation in a 9 T magnetic field were investigated. An anisotropic, ordered layer structure was achieved using [P3HT₂₀ -Zn-PEO₁₀₇ ] and carefully characterized by polarized optical microscopy (POM), AFM, polarized UV/Vis spectroscopy, and GI-SAXS/WAXS. The PEO-removed [P3HT₂₀ -Zn-PEO₁₀₇ ] film was obtained after decomplexation with TEA-EDTA under mild conditions, and the selective removal of PEO domains was evidenced by UV/Vis and ATR-FTIR spectroscopy. Anisotropic photoconductivity of the magnetically aligned film was evaluated by flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements. The results indicated that the presence of insulating crystalline PEO segments diminished the photoconductivity along the P3HT backbone direction.

Ring-Opening Polymerisation of Low-Strain Nickelocenophanes: Synthesis and Magnetic Properties of Polynickelocenes with Carbon and Silicon Main Chain Spacers

Polymetallocenes based on ferrocene, and to a lesser extent cobaltocene, have been well-studied, whereas analogous systems based on nickelocene are virtually unexplored. It has been previously shown that poly(nickelocenylpropylene) [Ni(η⁵ -C₅ H₄ )₂ (CH₂ )₃ ]_n is formed as a mixture of cyclic (6_x ) and linear (7) components by the reversible ring-opening polymerisation (ROP) of tricarba[3]nickelocenophane [Ni(η⁵ -C₅ H₄ )₂ (CH₂ )₃ ] (5). Herein the generality of this approach to main-chain polynickelocenes is demonstrated and the ROP of tetracarba[4]nickelocenophane [Ni(η⁵ -C₅ H₄ )₂ (CH₂ )₄ ] (8), and disila[2]nickelocenophane [Ni(η⁵ -C₅ H₄ )₂ (SiMe₂ )₂ ] (12) is described, to yield predominantly insoluble homopolymers poly(nickelocenylbutylene) [Ni(η⁵ -C₅ H₄ )₂ (CH₂ )₄ ]_n (13) and poly(tetramethyldisilylnickelocene) [Ni(η⁵ -C₅ H₄ )₂ (SiMe₂ )₂ ]_n (14), respectively. The ROP of 8 and 12 was also found to be reversible at elevated temperature. To access soluble high molar mass materials, copolymerisations of 5, 8, and 12 were performed. Superconducting quantum interference device (SQUID) magnetometry measurements of 13 and 14 indicated that these homopolymers behave as simple paramagnets at temperatures greater than 50 K, with significant antiferromagnetic coupling that is notably larger in carbon-bridged 6_x /7 and 13 compared to the disilyl-bridged 14. However, the behaviour of these polynickelocenes deviates substantially from the Curie-Weiss law at low temperatures due to considerable zero-field splitting.

Surface functionalized nanostructures via position registered supramolecular polymer assembly

Versatile control of cylindrical nanostructures formed by supramolecular assembly of end-functionalized polymer blends is demonstrated not only in their orientation over large areas but also in their surface chemical functionalities. Two binary blends consisting of supramolecular analogues of diblock copolymers with complementary end-sulfonated and aminated groups are investigated, viz., mono-end-functionalized polymers of (i) one-end-sulfonated polystyrene (SPS) and one-end-aminated poly(butadiene) (APBD) and (ii) one end-aminated polystyrene (APS) and one end-sulfonated poly(butadiene) (SPBD). The orientation of the cylinders with respect to the substrate surface depends on the solvent annealing time; either hexagonally ordered vertical cylinders or in-plane ones are readily obtained by controlling the solvent annealing time. Selective chemical etching of one of the polymers provides four different chemically modified nanostructures, viz., hexagonally ordered cylindrical holes and cylindrical posts with either sulfonate or amine surface functional groups. Additional supramolecular assembly is successfully achieved by solution coating either polymers or organic dyes that complementarily interact with the functional groups on the nanostructures. Furthermore, the supramolecularly assembled nanostructures are controlled by confining them to topographically pre-patterned Si substrates with pattern geometries of various shapes and sizes to produce globally ordered vertical or in-plane cylinders with chemical functionalities on their surfaces.

An asymmetric A-B-A' metallo-supramolecular triblock copolymer linked by Ni(2+)-bis-terpyridine complexes at one junction

A metallo-supramolecular triblock copolymer polystyrene-b-polyisoprene-[Ni(2+)]-polystyrene (SI-[Ni(2+)]-S') has been efficiently prepared using a one-pot, two-step procedure, where the blocks are held by bis-terpyridine complexes at the junction of SI-S'. This specific metallo-supramolecular chemistry is demonstrated to be a robust approach to potentially broaden the diversity of block copolymers. The location of the metal-ligand complexes has a profound influence on the phase separation of the triblock copolymer in the bulk, which results in a distinctive phase segregation between the end blocks and leads to an unexpected asymmetry of the triblock copolymer. The metal-ligand complexes are found to be preferentially located on the adjacent spherical domain and form a core-shell structure. The resulting multiphase material exhibits distinct elastomeric properties with significant toughness and creep recovery behavior. This type of triblock copolymer is anticipated to be a novel class of hybrid thermo-plastic elastomeric material with wide tunability and functionality.

Precise Control over the Rheological Behavior of Associating Stimuli-Responsive Block Copolymer Gels

"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.

Tailored pore sizes in integral asymmetric membranes formed by blends of block copolymers

A simple way to generate isoporous membranes with tailored pore sizes is shown. Block copolymers of different compositions are blended in solution, and membranes are obtained by solution casting followed by nonsolvent-induced phase separation. This enables the preparation of integral asymmetric membranes with a defined pore size for given sets of block copolymers just by choosing the right blend composition.

Metallo/clusto hybridized supramolecular polymers

The introduction of metal centers to a supramolecular polymer system is an important approach to fabricate hybrid supramolecular polymers with synergistic properties between their inorganic and organic components, which is mainly realized through two strategies: one is the embedment of metal ions through metal-ligand coordination to form metallo-supramolecular polymers (MSPs); the other is using metal-containing clusters as hybrid building blocks to prepare clusto-supramolecular polymers (CSPs). The available paradigms of MSPs and CSPs not only exhibit the unique functions of metal centers but also hold the good processing ability and the stimuli-responsibility of dynamically bonded polymeric structures, thus representing a new class of hybrid soft materials. In this review, the development and recent progress of MSPs and CSPs are discussed in detail, including their structure design, synthetic procedures and related properties. Finally, challenges and potential areas in metal-containing supramolecular polymers are outlooked.

Isoporous block copolymer membranes

The developments in membranes based on tailored block copolymers are reported with an emphasis on isoporous membranes. These membranes can be prepared in different geometries, namely flat sheets and hollow fibers. They display narrow pore size distributions due to their formation by self-assembly. The preparation of these membranes and possibilities to further functionalize such membranes will be discussed. Different ways to control the pore size will be addressed, and the potential of block copolymer blends to fabricate membranes with tailored pore sizes will be shown.

Facile Preparation of Supramolecular H-Shaped (Ter)polymers via Multiple Hydrogen Bonding

A well-defined Hamilton wedge (HW) midchain functionalized block copolymer, i.e., polyethylene glycol-b-polystyrene (PEG-HW-PS, M_n,GPC = 5600 Da, PDI = 1.03), was successfully synthesized via a combination of atom transfer radical polymerization (ATRP) and copper-catalyzed azide alkyne cycloaddition (CuAAC). An α,ω-cyanuric acid (CA) difunctional linear homopolymer poly(n-butylacrylate) (CA-PnBA-CA, M_n,GPC = 8100 Da, PDI = 1.09) was concomitantly prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Supramolecular H-shaped macromolecules were-for the first time-prepared through supramolecular self-assembly between HW and CA recognition motifs to generate (PS-b-PEG)·PnBA·(PS-b-PEG) and (PS-b-PS)·PnBA·(PS-b-PS) in CH₂Cl₂ or dichloromethane-d₂ at ambient temperature. The self-assembly process (at a total concentration of the two species of close to 4.5 mM) was evidenced by proton nuclear magnetic resonance (¹H NMR) spectroscopy, diffusion-ordered NMR spectroscopy (DOSY), and dynamic light scattering (DLS) analyses. The results derived via DOSY NMR experiments and DLS combined with a Job plot analysis and in-depth NMR titration experiments indicate that the formation of supramolecular H-shaped macromolecules in 2:1 stoichiometry is efficiently occurring via the employed complementary recognition motifs with high binding constants (between 1.2 and 1.5 × 10⁵ L mol^-1 at ambient temperature).