Highly Ordered Nanoporous Films from Supramolecular Diblock Copolymers with Hydrogen-Bonding Junctions

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.

A Versatile Assembly Approach toward Multifunctional Supramolecular Poly(Ionic Liquid) Nanoporous Membranes in Water

Hydrogen (H)-bonding-integration of multiple ingredients into supramolecular polyelectrolyte nanoporous membranes in water, thereby achieving tailor-made porous architectures, properties, and functionalities, remains one of the foremost challenges in materials chemistry due to the significantly opposing action of water molecules against H-bonding. Herein, a strategy is described that allows direct fusing of the functional attributes of small additives into water-involved hydrogen bonding assembled supramolecular poly(ionic liquid) (PIL) nanoporous membranes (SPILMs) under ambient conditions. It discloses that the pore size distributions and mechanical properties of SPILMs are rationally controlled by tuning the H-bonding interactions between small additives and homo-PIL. It demonstrates that, benefiting from the synergy of multiple noncovalent interactions, small dye additives/homo-PIL solutions can be utilized as versatile inks for yielding colorful light emitting films with robust underwater adhesion strength, excellent stretchability, and flexibility on diverse substrates, including both hydrophilic and hydrophobic surfaces. This system provides a general platform for integrating the functional attributes of a diverse variety of additives into SPILMs to create multifunctional and programmable materials in water.

Regioselective Seeded Polymerization in Block Copolymer Nanoparticles: Post-Assembly Control of Colloidal Features

Post-assembly modifications are efficient tools to adjust colloidal features of block copolymer (BCP) particles. However, existing methods often address particle shape, morphology, and chemical functionality individually. For simultaneous control, we transferred the concept of seeded polymerization to phase separated BCP particles. Key to our approach is the regioselective polymerization of (functional) monomers inside specific BCP domains. This was demonstrated in striped PS-b-P2VP ellipsoids. Here, polymerization of styrene preferably occurs in PS domains and increases PS lamellar thickness up to 5-fold. The resulting asymmetric lamellar morphology also changes the particle shape, i.e., increases the aspect ratio. Using 4-vinylbenzyl azide as co-monomer, azides as chemical functionalities can be added selectively to the PS domains. Overall, our simple and versatile method gives access to various multifunctional BCP colloids from a single batch of pre-formed particles.

Solvent Annealing of Striped Ellipsoidal Block Copolymer Particles: Reversible Control over Lamellae Asymmetry, Aspect Ratio, and Particle Surface

Solvent annealing is a versatile tool to adjust the shape and morphology of block copolymer (BCP) particles. During this process, polar solvents are often used for block-selective swelling. However, such water-miscible solvents can induce (partial) solubilization of one block in the surrounding aqueous medium, thus, causing complex structural variations and even particle disassembly. To reduce the complexity in morphology control, we focused on toluene as a nonpolar polystyrene-selective solvent for the annealing of striped polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) ellipsoids. The selective stretching of PS chains produces unique asymmetric lamellae structures, which translate to an increase in the particle aspect ratio after toluene evaporation. Complete reversibility is achieved by changing to chloroform as a nonselective solvent. Moreover, surfactants can be used to tune block-selective wetting of the particle surface during the annealing; for example, a PS shell can protect the internal lamellae structure from disassembly. Overall, this versatile postassembly process enables the tailoring of the structural features of striped colloidal ellipsoids by only using commercial BCPs and solvents.

Hydrogen-bonding mediated self-assembly of amphiphilic ABA triblock copolymers into well-defined giant vesicles

A straightforward and efficient access towards the generation of well-defined giant vesicles (∼3 μm in diameters), featured by Hydrogen-bonded DAP–DAP dimerization, and the amphiphilic interactions is reported.

100th Anniversary of Macromolecular Science Viewpoint: Modeling and Simulation of Macromolecules with Hydrogen Bonds: Challenges, Successes, and Opportunities

Macromolecular materials with directional interactions such as hydrogen bonds exhibit numerous attractive features in terms of structure, thermodynamics, and dynamics. Besides enabling precise tuning of desirable geometries in the assembled state (e.g., programmable coordination numbers depending on the valency of the directional interaction), mixing in a blend/composite through stabilization via hydrogen bonds between the various components, hydrogen bonds can also impart responsiveness to external stimuli (e.g., temperature, pH). In biomacromolecules (e.g., proteins, DNA, polysaccharides), hydrogen bonds play a key role in stabilizing secondary and tertiary structures, which in turn define the function of these macromolecules. In this Viewpoint, I present the challenges, successes, and opportunities for molecular modeling and simulations to conduct fundamental and application-focused research on macromolecular materials with hydrogen bonding interactions. The past successes and limitations of atomistic simulations are discussed first, followed by highlights from recent developments in coarse-grained modeling and their use in studies of (synthetic and biologically relevant) macromolecular materials. Model development focused on polynucleotides (e.g., DNA, RNA, etc.), polypeptides, polysaccharides, and synthetic polymers at experimentally relevant conditions are highlighted. This viewpoint ends with potential future directions for macromolecular modeling and simulations with other types of directional interactions beyond hydrogen bonding.

Simulation Study of Process-Controlled Supramolecular Block Copolymer Phase Separation with Reversible Reaction Algorithm

A supramolecular diblock copolymer formed by reversible bonds between the two blocks shows a rich microphase separation behavior and has great application potential in stimuli-responsive materials. We propose a novel method to describe supramolecular reactions in dissipative particle dynamics, which includes a reversible reaction to accurately reproduce the strength, saturation, and dynamic properties of the reversible bonds in the simulations. The thermodynamic properties and dynamic processes of the supramolecular diblock copolymer melts in both equilibrium and non-equilibrium states were studied using this method. The simulation results show that the method can faithfully characterize phase behaviors and dynamic properties of supramolecular diblock copolymer melts, especially in a non-equilibrium state, which provides a novel tool to unveil self-assembly mechanism and describe the properties of supramolecular block copolymers.

Engineering the morphology of hydrogen-bonded comb-shaped supramolecular polymers: from solution self-assembly to confined assembly

A library of nanostructures and multi-stage morphology transformation are realized by introducing a 3D confined assembly to hydrogen-bonded comb-shaped supramolecular polymer architectures.

Adaptable and Reprogrammable Surfaces

Establishing control over chemical reactions on interfaces is a key challenge in contemporary surface and materials science, in particular when introducing well-defined functionalities in a reversible fashion. Reprogrammable, adaptable and functional interfaces require sophisticated chemistries to precisely equip them with specific functionalities having tailored properties. In the last decade, reversible chemistries-both covalent and noncovalent-have paved the way to precision functionalize 2 or 3D structures that provide both spatial and temporal control. A critical literature assessment reveals that methodologies for writing and erasing substrates exist, yet are still far from reaching their full potential. It is thus critical to assess the current status and to identify avenues to overcome the existing limitations. Herein, the current state-of-the-art in the field of reversible chemistry on surfaces is surveyed, while concomitantly identifying the challenges-not only synthetic but also in current surface characterization methods. The potential within reversible chemistry on surfaces to function as true writeable memories devices is identified, and the latest developments in readout technologies are discussed. Finally, we explore how spatial and temporal control over reversible, light-induced chemistries has the potential to drive the future of functional interface design, especially when combined with powerful laser lithographic applications.

Morphology and thermodynamics of polymers with monofunctional hydrogen bonding ends in dilute and semidilute concentration

Rheological properties of supramolecular polymers (SMPs) depend on their equilibrium structure including the size, the number, and the topology of aggregates. A polymer with a hydrogen bonding (H-bonding) motif at both ends is one widely used precursor to build SMPs. Due to the complex interplay between chain stiffness, H-bonding interaction, polarity along a chain, and polymer conformational entropy, it is difficult to theoretically predict the structure of SMPs. In this work we investigate thermodynamics of SMPs with H-bonding ends in a wide range of densities. A replica exchange stochastic approximation Monte Carlo method with coarse-grained models for polyethylene and polybuthylene glycols is used. Our simulation shows that SMPs have two morphological transition lines with increasing temperature, a ring-linear transition, and a linear-free chain transition. The latter is a thermodynamic transition and turns out to be continuous. Comparing the two different spacers, we find that ring-linear transition temperatures differ from each other at the constant volume fraction due to different looping probabilities, which can be calculated from the average polymer size by mean field. However, the linear-free chain transition temperatures are similar because the entropic penalty to form a hydrogen bond mainly depends on the probability of finding H-bonding groups in a system, which is the same for both systems at a given volume fraction.

Preparation of lactic acid- and glucose-responsive poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymer micelles using phenylboronic ester as a sensitive block linkage

The present study describes the synthesis, self-assembly and responsiveness to glucose and lactic acid of biocompatible and biodegradable block copolymer micelles using phenylboronic ester as the linkage between hydrophobic poly(ε-caprolactone) (PCL) and hydrophilic poly(ethylene oxide) (PEO). The PCL block with pendant phenylboronic acid (PCLBA) was synthesized by combining ε-caprolactone (ε-CL) ring-opening polymerisation (ROP), using 4-hydroxymethyl(phenylboronic) acid pinacolate as the initiator, and pinacol deprotection. The glucose-terminated PEO (PEOGlc) was prepared by 1,3-dipolar, Cu(i)-catalysed, alkyne-azide cycloaddition of α-methoxy-ω-propargyl poly(ethylene oxide) and 1-azido-1-deoxy-d-glucopyranose. All new compounds were evaluated by 1H NMR spectroscopy and by SEC analysis. PCLBA and PEOGlc blocks were linked in NaOH acetone solution, which was indirectly confirmed by Alizarin Red S fluorescence and directly by 1H NMR spectroscopy. Dialysis against Milli-Q water induced the self-assembly of PCLBA-b-PEOGlc nanoparticles, which were characterised by static (SLS) and dynamic (DLS) light scattering and by cryogenic transmission electron microscopy (cryo-TEM). Furthermore, the microscopic properties of the charged interface between the hydrophobic PCLBA core and the hydrophilic PEOGlc shell were examined by electrophoretic light scattering (zeta potential) and by fluorescence spectroscopy using the fluorescent probe 5-(N-dodecanoyl)aminofluorescein (DAF) as a pH indicator. Subsequently, the nanoparticles were transferred to a phosphate buffer saline (PBS) solution supplemented with different concentrations of glucose to simulate the physiological conditions in blood or lactic acid to simulate acidic cytosolic or endosomal conditions in tumour cells. Adding a surplus of glucose or lactic acid, which competitively binds to PBA, removes the stabilising hydrophilic PEOGlc blocks, thereby triggering marked nanoparticle aggregation. However, the rate of aggregation induced by lactic acid is considerably faster than that induced by glucose, as confirmed by light scattering. Thus, this novel block copolymer may contribute to the field of selective, lactic acid- and/or glucose-responsive drug delivery vehicle design under both pathological and physiological conditions.

Core cross-linked double hydrophilic block copolymer micelles based on multiple hydrogen-bonding interactions

Facile preparation and characterization of core cross-linked micelles via strong multiple hydrogen bonds using well-defined thermo-responsive double hydrophilic block copolymers.

Threading through Macrocycles Enhances the Performance of Carbon Nanotubes as Polymer Fillers

In this work, we study the reinforcement of polymers by mechanically interlocked derivatives of single-walled carbon nanotubes (SWNTs). We compare the mechanical properties of fibers made of polymers and of composites with pristine SWNTs, mechanically interlocked derivatives of SWNTs (MINTs), and the corresponding supramolecular models. Improvements of both Young's modulus and tensile strength of up to 200% were observed for the polystyrene-MINT samples with an optimized loading of just 0.01 wt %, while the supramolecular models with identical chemical composition and loading showed negligible or even detrimental influence. This behavior is found for three different types of SWNTs and two types of macrocycles. Molecular dynamics simulations show that the polymer adopts an elongated conformation parallel to the SWNT when interacting with MINT fillers, irrespective of the macrocycle chemical nature, whereas a more globular structure is taken upon facing with either pristine SWNTs or supramolecular models. The MINT composite architecture thus leads to a more efficient exploitation of the axial properties of the SWNTs and of the polymer chain at the interface, in agreement with experimental results. Our findings demonstrate that the mechanical bond imparts distinctive advantageous properties to SWNT derivatives as polymer fillers.

Dynamic Ordering and Phase Segregation in Hydrogen-Bonded Polymers

Hydrogen bonds (H-bonds) constitute highly relevant structural units of molecular self-assembly. They bridge biological and synthetic sciences, implementing dynamic properties into materials and molecules, not achieved via purely covalent bonds. Phase segregation on the other hand represents another important assembly principle, responsible for, e.g., cell compartimentation, membrane-formation, and microphase segregation in polymers. Yet, despite the expanding elegant synthetic strategies of supramolecular polymers, the investigation of phase behavior of macromolecules driven by H-bonding forces still remains in its infancy. Compared to phase segregation arising from covalently linked block copolymers, the generation of phase segregated nanostructures via supramolecular polymers facilitates the design of novel functional materials, such as those with stimuli-responsive, self-healing, and erasable-material properties. We here discuss the phase segregation of H-bonding polymers in both the solution and solid state, wherein the molecular recognition elements are based on multiple H-bonding moieties, such as thymine/2,6-diamino-pyridine (THY/DAP), thymine/diamino triazine (THY/DAT), and barbiturate/Hamilton wedge (Ba/HW) elements. The specific aggregation of a series of different H-bonding polymers in solution, both linear and dendritic polymers, bearing heterocomplementary H-bonding moieties are described, in particular focusing on the issue of phase segregation. The exploitation of H-bonded supramolecular dendrons with segregating polymer chains leads to the formation of three-phase segregated hierarchical micelles in solution, purely linking the components via H-bonds, in turn displaying a versatile spectrum of segregated morphologies. We also focus on segregation effects of H-bonded amorphous and crystalline polymers: thus the formation of nanostructures, such as disordered micelles and well-ordered body centered cubic (BCC) packed spheres from telechelic polymers bearing H-bonding moieties at the chain ends is observed. Finally, we discuss the discovery of novel functional microphase separated self-healing supramolecular architectures, illustrating dynamic and self-healing properties with an almost complete recovery of the initial mechanical performances healing within 24h at 30 °C. Collectively, our studies prove that phase segregation in H-bonding polymers is an important principle, capable to generate nanostructures and dynamic properties not achieved in covalently linked polymers. The results discussed illustrate that a rational architectural design within H-bonding polymer systems in interplay with phase segregation in both the amorphous and crystalline state opens perspectives to develop artificial supramolecular systems approaching the level of complexities and properties present in nature's biomaterials.

Hierarchical Micelles via Polyphilic Interactions: Hydrogen-Bonded Supramolecular Dendrons and Double Immiscible Polymers

We report a simple strategy to form three-phase segregated hierarchical micelles via a counterbalanced phase segregation/self-assembly process. Our methodology relies on a cooperative polyphilic phase segregation, paralleled by a self-assembly process induced by hydrogen-bonds to afford the generation of supramolecular multicompartment dendrons. The versatile preparation of such hierarchical morphologies is evidenced on the basis of a series of supramolecular dendrons, composed of semifluorinated copolymers, homopolymers, or nonfluorinated polymers. We do have designed and prepared mid- and α,ω-barbiturate (Ba) functionalized poly(n-butyl acrylates), Ba-(PnBuA-Ba)2, together with a series of heterocomplementary α,ω-Hamilton wedge (HW) functionalized polymers via reversible addition-fragmentation chain transfer (co)polymerization. To enable subtle phase segregation processes, the semifluorinated homo- and copolymers HW-P(nBuA-co-PFPA)-HW (prepared via copolymerization of nBuA with 2,2,3,3,3-pentafluoropropyl acrylate (PFPA)) and HW-PPFPA-HW, as well as the nonfluorinated polymer HW-PnBuA-HW and HW-PI-HW (PI, polyisoprene), have been generated. Selective intermolecular complexation between Ba-(PnBuA-Ba)2 and the complementary polymers (such as HW-P(nBuA-co-PFPA)-HW, HW-PPFPA-HW or HW-PI-HW) leads to the successful generation of supramolecular dendrons as evidenced by (1)H NMR and diffusion-ordered NMR spectroscopy, together with the formation of well-defined disc-like nano-objects as demonstrated by microscopy investigations. Transmission electron microscopy demonstrates a unique, uncommon phase behavior showing remarkable three-phase segregated hierarchical micelles, indicative of the desired micellar multicompartments.

Recodable surfaces based on switchable hydrogen bonds

We introduce recodable surfaces solely based on reversible artificial hydrogen bonding interactions.

Periodic introduction of a Hamilton receptor into a polystyrene backbone for a supramolecular graft copolymer with regular intervals

The Hamilton receptor group (–DADDAD–; D = hydrogen donor; A = hydrogen acceptor) was periodically introduced into a polystyrene backbone, starting from the ruthenium-catalyzed living radical polymerization of styrene with the Hamilton receptor-based bifunctional initiator.

Versatile self-assembly of supramolecular block copolymers with ionic cluster junctions

Clusto-supramolecular block copolymers were prepared by using an inorganic cluster [W₆O₁₉]²⁻ as an ionic junction, which exhibited versatile self-assembly behaviours.

One-pot synthesis and self-assembly of supramolecular dendritic polymers

A X–Y₂ type heterotropic single-chain polymer, Ba-(PnBuA-HW)₂, is prepared in a one-pot two-step reaction, subsequently self-assembling into supramolecular dendrimers, which are displaying solvent-dependent disc-like hierarchical nanoscopic structures as evidenced by AFM.