Dynamics and healing behavior of metallosupramolecular polymers

Light-Triggered Switching of Metallosupramolecular Polymer Systems

Metallosupramolecular polymers (MSPs) are formed through the formation of coordination complexes between monomers that contain multiple ligands and suitable metal salts. The assembly of MSPs is generally dynamic and reversible, which leads to stimuli-responsive materials and enables functions such as healing or recycling. Heat is arguably the most widely employed stimulus to manipulate MSPs, but the level of control that can be achieved is limited. Here, we report light-responsive MSP systems, whose response is based on an opto-chemical transduction principle. We combined the photoacid generator 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (MBTT) with poly(acrylates) that comprise a few mol % of the 2,6-bis(1'-methyl-benzimidazolyl)pyridine (Mebip) ligand. The latter forms supramolecular cross-links upon the addition of metal salts, such as Zn2+, Eu3+, and Cu2+. We utilized titration experiments, optical spectroscopy, and rheology on model compounds and polymer systems to demonstrate that the MSP network can be rapidly disassembled upon optical activation of the photoacid generator, on account of protonation of the ligand and dissociation of the ML complex. Optorheological experiments reveal that the rheological properties of gels based on the MSP network, MBTT, and chlorobenzene can be drastically altered in an on-demand fashion by exposure to UV light.

Self-healing behavior of superhard covalent bond materials

In recent years, superhard covalently bonded materials have drawn a great deal of attention due to their excellent mechanical properties and potential applications in various fields. This review focuses on the self-healing behavior of these materials, outlining state-of-the-art research results. In detail, we discuss current self-healing mechanisms of self-healing materials including extrinsic healing mechanisms (such as microencapsulation, oxidative healing, shape memory, etc.) and intrinsic healing (dynamic covalent bonding, supramolecular interactions, diffusion, defect-driven processes, etc.). We also provide an overview of the progress in the self-healing behavior of superhard covalently bonded materials and the mechanisms of permanent covalent bonding healing. Additionally, we analyze the factors that influence the healing properties of these materials. Finally, the main findings and an outlook on the future directions and challenges of this emerging field are summarized in the Conclusion section.

Should I stay or should I flow? An exploration of phase-separated metallosupramolecular liquid crystal polymers

Dynamic liquid crystalline polymers (dLCPs) incorporate both liquid crystalline mesogens and dynamic bonds into a single polymeric material. These dual functionalities impart order-dependent thermo-responsive mechano-optical properties and enhanced reprocessability/programmability enabling their use as soft actuators, adaptive adhesives, and damping materials. While many previous works studying dynamic LCPs utilize dynamic covalent bonds, metallosupramolecular bonds provide a modular platform where a series of materials can be accessed from a single polymeric feedstock through the variation of the metal ion used. A series of dLCPs were prepared by the addition of metal salts to a telechelic 2,6-bisbenzimidazolylpyridine (Bip) ligand endcapped LCP to form metallosupramolecular liquid crystal polymers (MSLCPs). The resulting MSLCPs were found to phase separate into hard and soft phases which aids in their mechanical robustness. Variations of the metal salts used to access these materials allowed for control of the thermomechanical, viscoelastic, and adhesive properties with relaxations that can be tailored independently of the mesogenic transition. This work demonstrates that by accessing phase separation through the incorporation of metallosupramolecular moieties, highly processable yet robust MSLCP materials can be realized. This class of materials opens the door to LCPs with bulk flow behavior that can also be utilized as multi-level adhesives.

Tailoring dual cross-linked polymer-ionic liquid composites by blending co-crystallizable polymers for stretchable electronics

Facile adjustment of the behavior of dual cross-linked polymer-ionic liquid composites (PICs) for stretchable electronics was achieved via solution blending of two copolymers having the same monomer pairs. Two poly(docosyl acrylate-r-tert-butyl acrylate) (poly(A22-r-tBA)) copolymers with different molar ratios were synthesized and solution-cast with ionic liquids (ILs) to fabricate ternary PICs. The phase behavior and the thermal and structural properties of the composites were investigated by varying the mixing ratio, providing insights into the cross-linking mechanisms. The observed changes enabled systematic modulation of the stretchability, thermal stability, and self-healing capability of PICs, which are crucial attributes of wearable devices. Mechanically tough and conductive PICs were utilized in fabricating strain sensors capable of detecting human motion.

Molecular control via dynamic bonding enables material responsiveness in additively manufactured metallo-polyelectrolytes

Metallo-polyelectrolytes are versatile materials for applications like filtration, biomedical devices, and sensors, due to their metal-organic synergy. Their dynamic and reversible electrostatic interactions offer high ionic conductivity, self-healing, and tunable mechanical properties. However, the knowledge gap between molecular-level dynamic bonds and continuum-level material properties persists, largely due to limited fabrication methods and a lack of theoretical design frameworks. To address this critical gap, we present a framework, combining theoretical and experimental insights, highlighting the interplay of molecular parameters in governing material properties. Using stereolithography-based additive manufacturing, we produce durable metallo-polyelectrolytes gels with tunable mechanical properties based on metal ion valency and polymer charge sparsity. Our approach unveils mechanistic insights into how these interactions propagate to macroscale properties, where higher valency ions yield stiffer, tougher materials, and lower charge sparsity alters material phase behavior. This work enhances understanding of metallo-polyelectrolytes behavior, providing a foundation for designing advanced functional materials.

Metallo-Supramolecular Helical Fibres from Chiral Phenylacetylene Monomers: Cation Induced Self-Assembly

Chiral metallo-supramolecular fibres can be easily obtained by mixing a chloroform solution of a phenylacetylene monomer (PA) that bears a chiral sulfoxide group as pendant, with different equivalents of a methanolic solution of AgClO4 . Thus, while the PA is found molecularly dissolved in chloroform, the addition of Ag+ ions induce its aggregation through the formation of an axially chiral metallo-supramolecular aggregate with high thermal stable properties. In this case, the ability of the metal ion to coordinate the PA triple bond, combined with the argentophilicity of the metal ion and the planarity of the phenylacetylene drives to the formation of a helical coordination polymer, whose P or M axial chirality is determined by the chirality of the sulfoxide used as substituent of the PA. Depending on the PA/Ag+ (mol/mol) ratio, it is possible to tune the morphology of the metallo-supramolecular aggregate from chiral fibers to chiral gel.

Structure and Properties of Metallosupramolecular Polymers with a Nitrogen-Based Bidentate Ligand

The solid-state properties of supramolecular polymers that feature metal-ligand (ML) complexes are, in addition to the general nature of the monomer, significantly affected by the choice of ligand and metal salt. Indeed, the variation of these components can be used to alter the structural, thermal, mechanical, and viscoelastic properties over a wide ranges. Moreover, the dynamic nature of certain ML complexes can render the resulting metallosupramolecular polymers (MSPs) stimuli-responsive, enabling functions such as healing, reversible adhesion, and mechanotransduction. We here report MSPs based on the bidentate ligand 6-(1'-methylbenzimidazolyl) pyridine (MBP), which is easily accessible and forms threefold coordination complexes with various transition metal ions. Thus, a poly(ethylene-co-butylene) telechelic was end-functionalized with two MBP ligands and the resulting macromonomer was assembled with the triflate salts of either Zn2+, Fe2+, or Ni2+. All three MSPs microphase separate and adopt, depending on the metal ion and thermal history, lamellar or hexagonal morphologies with crystalline domains formed by the ML complexes. The melting transitions are well below 200 °C, and this permits facile (re)processing. Furthermore, defects can be readily and fully healed upon exposure to UV-light. While the three MSPs display similar moduli in the rubbery regime, their extensibility and tensile strength depend on the nature of the ML complex, which similarly affects the long-range order and dynamic behavior.

Hyperbranched Polymers for Organic Semiconductors

Hyperbranched polymers (HBPs) have attracted increasing attention owing to their distinct highly branched topological structures, resulting in unique properties and wide applications in organic semiconductors (OSCs). In this Review, recent progress in functional HBPs is outlined in the field of OSCs, including organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), dye-sensitized solar cells (DSSCs), and organic field effect transistors (OFETs), among others. Prospects of HBPs-based materials in OSCs are examined. The results revealed that multi-dimensional topologies not only regulate the electron (hole) transport but also adjust the film morphology, thereby affecting the efficiency and long life of organic electronic devices. Many studies showed the usefulness of HBPs as hole transport materials but reports dealing with n-type and ambipolar materials are still lacking. In addition, the interchain covalent bond in hyperbranched polymers could mitigate the damage caused by stretching, conducive to building stable flexible stretchable devices with long-term durability and good safety under harsh environmental conditions. Overall, the flexible stretchable design may enrich the applications of HBPs in organic semiconductors and provide new ideas for guiding the future design of functional organic semiconductor materials.

Autonomous alignment and healing in multilayer soft electronics using immiscible dynamic polymers

Self-healing soft electronic and robotic devices can, like human skin, recover autonomously from damage. While current devices use a single type of dynamic polymer for all functional layers to ensure strong interlayer adhesion, this approach requires manual layer alignment. In this study, we used two dynamic polymers, which have immiscible backbones but identical dynamic bonds, to maintain interlayer adhesion while enabling autonomous realignment during healing. These dynamic polymers exhibit a weakly interpenetrating and adhesive interface, whose width is tunable. When multilayered polymer films are misaligned after damage, these structures autonomously realign during healing to minimize interfacial free energy. We fabricated devices with conductive, dielectric, and magnetic particles that functionally heal after damage, enabling thin-film pressure sensors, magnetically assembled soft robots, and underwater circuit assembly.

Synthesis of platinum(II)-complex end-tethered polymers: spectroscopic properties and nanostructured particles

Although metal-containing polymers have been widely studied as a novel class of functional soft materials, the microphase separation between polymeric segments and metal-ligand complexes has been less addressed, which is critical to control their structures and functions. To do this, short-chain polystyrenes (PSs) have been end-functionalized with nanosized square-planar platinum(II) complexes. The platinum(II)-comprising polymers were found to show significant luminescence enhancement in chloroform/methanol solvent mixtures upon increasing the methanol composition. By modulating both the PS length and solvent quality, various self-assembled morphologies formed controllably in the mixed solvents and typical examples include nanofibers, nanoellipsoids, and nanospheres. More interestingly, the inside structures of these polymer particles are shown to be lamellar with sub-10 nm spacings, wherein the PS blocks are alternatively aligned with the platinum(II) units. Such a luminescence enhancement and hierarchical nanostructured particles originate from a subtle combination of directional Pt(II)⋯Pt(II) and/or π-π stacking interactions between the platinum(II) units and the solvophobic effect between the PS blocks. This work suggests that by microphase separating polymer chains with nanosized metal-ligand complexes, metal-containing polymers can self-assemble to form sub-10 nm scale nanostructures showcasing desired properties and functions.

Intrinsically Self-Healing Polymers: From Mechanistic Insight to Current Challenges

Self-healing materials open new prospects for more sustainable technologies with improved material performance and devices' longevity. We present an overview of the recent developments in the field of intrinsically self-healing polymers, the broad class of materials based mostly on polymers with dynamic covalent and noncovalent bonds. We describe the current models of self-healing mechanisms and discuss several examples of systems with different types of dynamic bonds, from various hydrogen bonds to dynamic covalent bonds. The recent advances indicate that the most intriguing results are obtained on the systems that have combined different types of dynamic bonds. These materials demonstrate high toughness along with a relatively fast self-healing rate. There is a clear trade-off relationship between the rate of self-healing and mechanical modulus of the materials, and we propose design principles of polymers toward surpassing this trade-off. We also discuss various applications of intrinsically self-healing polymers in different technologies and summarize the current challenges in the field. This review intends to provide guidance for the design of intrinsic self-healing polymers with required properties.

Effect of Counterions on the Physicomechanical Properties of Copper-Nitrogen-Coordinated Metallosupramolecular Elastomers

Metallosupramolecular elastomers have attracted much attention due to their excellent mechanical properties, flexible tailoring of performance, and responsiveness to photo and thermal stimuli. The physicomechanical properties of metallosupramolecular elastomers are highly dependent on metal salts and ligand units; however, the role of counterions lacks practical exploration. To this end, we synthesized a simple acrylate copolymer model and introduced copper salts with different counterions to construct dynamic copper-nitrogen coordination cross-linked networks. This approach generated a series of elastomers with a tensile strength of over 10 MPa and a laser self-healing efficiency of over 90% within 2 min. In particular, we studied the effects of counterions on the thermodynamic, viscoelastic, mechanical, photothermal, and self-healing properties of the materials. Therefore, this work can provide instruction for the preparation and performance tailoring of metallosupramolecular elastomers.

Plasticization of a Semicrystalline Metallosupramolecular Polymer Network

The assembly of ligand-functionalized (macro)monomers with suitable metal ions affords metallosupramolecular polymers (MSPs). On account of the reversible and dynamic nature of the metal-ligand complexes, these materials can be temporarily (dis-)assembled upon exposure to a suitable stimulus, and this effect can be exploited to heal damaged samples, to facilitate processing and recycling, or to enable reversible adhesion. We here report on the plasticization of a semicrystalline, stimuli-responsive MSP network that was assembled by combining a low-molecular-weight building block carrying three 2,6-bis(1'-methylbenzimidazolyl) pyridine (Mebip) ligands and zinc bis(trifluoromethylsulfonyl)imide (Zn(NTf₂)₂). The pristine material exhibits high melting (T _m = 230 °C) and glass transition (T _g ≈ 157 °C) temperatures and offers robust mechanical properties between these temperatures. We show that this regime can be substantially extended through plasticization. To achieve this, the MSP network was blended with diisodecyl phthalate. The weight fraction of this plasticizer was systematically varied, and the thermal and mechanical properties of the resulting materials were investigated. We show that the T _g can be lowered by more than 60 °C and the toughness above the T _g is considerably increased.

Advances and Challenges of Self-Healing Elastomers: A Mini Review

In the last few decades, self-healing polymeric materials have been widely investigated because they can heal the damages spontaneously and thereby prolong their service lifetime. Many ingenious synthetic procedures have been developed for fabricating self-healing polymers with high performance. This mini review provides an impressive summary of the self-healing polymers with fast self-healing speed, which exhibits an irreplaceable role in many intriguing applications, such as flexible electronics. After a brief introduction to the development of self-healing polymers, we divide the development of self-healing polymers into five stages through the perspective of their research priorities at different periods. Subsequently, we elaborated the underlying healing mechanism of polymers, including the self-healing origins, the influencing factors, and direct evidence of healing at nanoscopic level. Following this, recent advance in realizing the fast self-healing speed of polymers through physical and chemical approaches is extensively overviewed. In particular, the methodology for balancing the mechanical strength and healing ability in fast self-healing elastomers is summarized. We hope that it could afford useful information for research people in promoting the further technical development of new strategies and technologies to prepare the high performance self-healing elastomers for advanced applications.

Supramolecular hyperbranched polymer gels based on pillar[5]arene and their applications in removal of micropollutants from water

Two kinds of pillar[5]arene-based supramolecular hyperbranched polymer gels were constructed and applied to efficiently remove micropollutants from water.

A healable, re-cyclable and thermochromic epoxy resin for thermal-responsive smart windows

Traditional thermoset polymers such as epoxy resin have strong mechanical strength, but are difficult to recycle, reshape and reprocess after being cured. When these materials are damaged, they can only...