Role of Metal–Ligand Bond Strength and Phase Separation on the Mechanical Properties of Metallopolymer Films

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.

A Toughening and Anti-Counterfeiting Benzotriazole-Based High-Performance Polymer Film Driven by Appropriate Intermolecular Coordination Force

It is of great significance to circumvent the inherent trade-off between strength and extensibility for epoxy resins. Herein dynamic Cu-benzotriazole cross-links are incorporated, as the appropriate intermolecular coordination interaction, into high performance epoxy networks, and the resulting epoxy resins exhibits outstanding thermal stability and mechanical properties, their strength and extensibility are simultaneously improved. Additionally, local manipulation of coordination crosslinking confers the film with anti-counterfeiting function.

Bridging experiments and theory: isolating the effects of metal-ligand interactions on viscoelasticity of reversible polymer networks

Polymer networks cross-linked by reversible metal-ligand interactions possess versatile mechanical properties achieved simply by varying the metal species and quantity. Although prior experiments have revealed the dependence of the network's viscoelastic behavior on the dynamics of metal-ligand interaction, a theoretical framework with quantitative relations that would enable efficient material design, is still lacking. One major challenge is isolating the effect of metal-ligand interaction from other factors in the polymer matrix. To address this challenge, we designed a linear precursor free from solvents, chain entanglements and polymer-metal phase separation to ensure that relaxation of the network is mainly governed by the dissociation and association of the metal-ligand cross-links. The rheological behavior of the networks was thoroughly characterized regarding the changes in cross-link density, binding stoichiometry and coordination stability, allowing quantitative comparison between experimental results and the sticky Rouse model. Through this process, we noticed that the presence of reversible cross-links increases the network modulus at high frequency compared to the linear polymer, and that the effective metal-ligand dissociation time increases dramatically with increasing the cross-link density. Informed by these findings, we modified the expression of the sticky Rouse model. For the polymer in which the metal center and ligands bond in a paired association, the relaxation follows our enhanced sticky Rouse model. For the polymer in which each reversible cross-link consists of multiple metal centers and ligands, the relaxation timescale is significantly extended due to greater restriction on the polymer chains. This systematic study bridges experiments and theory, providing deeper understanding of the mechanical properties of metallopolymers and facilitating material design.

Robust, Reprocessable, and Reconfigurable Cellulose-Based Multiple Shape Memory Polymer Enabled by Dynamic Metal-Ligand Bonds

Smart materials with multiple shape memory capacities have gradually attracted the interest of a lot of researchers due to their potential application in textiles, smart actuators, and aerospace engineering. However, the design and sustainable synthesis of multiple shape memory polymers (SMPs) simultaneously possessing robust mechanical strength, reprocessability, and reconfigurability still remain full of challenges. Starting from a readily available biomass material cellulose, a well-defined SMP, cellulose-graft-poly(n-butyl acrylate-co-1-vinylimidazole) copolymer (Cell-g-(BA-co-VI)) was facilely synthesized by addition-fragmentation chain transfer polymerization (RAFT) and the subsequent metallosupramolecular cross-linking. Taking advantage of the dynamic bonding, i.e., the rapid reversible fragmentation and the formation of metal ion-imidazole coordination, polymer networks with highly tunable mechanical properties, excellent solid-state plasticity, and quadruple-shape memory capacity are handily attainable. Microscopically, the metal-ligand clusters have a strong tendency to phase segregate from the soft grafted copolymers indicated by atomic force microscopy (AFM), and these serve as netpoints to construct novel SMPs. This article represents our new exploration of the next-generation SMPs based on cellulose backbone where carrying with supramolecular cross-linked soft grafted copolymers. This architecture design allows achieving robust, reprocessable, and reconfigurable thermoplastic SMPs that are difficult to realize by many other methods. Integrating these properties into one system in a synergetic manner also provides a novel approach to the high value addition application of cellulose in the fabrication of advanced functional materials.

One-pot synthesis of dual supramolecular associative copolymers by using a novel acrylate monomer bearing urethane and pendant pyridine groups

A highly efficient, one-pot synthesis of dual supramolecular associative copolymers is demonstrated by utilizing a novel acrylate monomer bearing urethane and pendant pyridine groups.

Preparation of metallosupramolecular single-chain polymeric nanoparticles and their characterization by Taylor dispersion

Polymers with pendant ligands furnish single-chain polymeric nanoparticles upon intramolecular metal–ligand complex formation with different metal-ions and Taylor dispersion analysis is employed to reliably characterize the dispersed particles.

Indole-based high-performance polymeric materials with enhanced mechanical and thermal properties via cation-π interaction

The preparation of high-performance polymeric materials with both excellent overall mechanical properties and heat resistance remains a considerable challenge. Inspired by the delicate self-assembly processes in nature, a facile strategy is reported for the preparation of high-performance polymeric materials with enhanced mechanical strength and improved thermal stability. In this instance, we successfully constructed a cation- π cross-linked polyimide (Na-poly(aryl indole) imide (Na-PINI)) film with enhanced mechanical performance and heat resistance (∼490°C). This work presents an innovative design strategy for realizing robust polymeric materials with integrated strength and thermal stability; the cation- π interaction is demonstrated to be a new method that may achieve many useful properties for high-performance polymers.

Metallopolymers for advanced sustainable applications

Since the development of metallopolymers, there has been tremendous interest in the applications of this type of materials. The interest in these materials stems from their potential use in industry as catalysts, biomedical agents in healthcare, energy storage and production as well as climate change mitigation. The past two decades have clearly shown exponential growth in the development of many new classes of metallopolymers that address these issues. Today, metallopolymers are considered to be at the forefront for discovering new and sustainable heterogeneous catalysts, therapeutics for drug-resistant diseases, energy storage and photovoltaics, molecular barometers and thermometers, as well as carbon dioxide sequesters. The focus of this review is to highlight the advances in design of metallopolymers with specific sustainable applications.

A facile approach to thermomechanically enhanced fatty acid-containing bioplastics using metal–ligand coordination

Dynamic metal–ligand coordination creates physical crosslinking and thus improves chain entanglements for enhancing the thermomechanical properties of biobased polymers.

Oxidative Layer-By-Layer Multilayers Based on Metal Coordination: Influence of Intervening Graphene Oxide Layers

Layer-by-layer (LbL) fabricated oxidative multilayers consisting of successive layers of inorganic polyphosphate (PP) and Ce(IV) can electrolessly form thin conducting polymer films on their surface. We describe the effect of substituting every second PP layer in the (PP/Ce) multilayers for graphene oxide (GO) as a means of modifying the structure and mechanical properties of these (GO/Ce/PP/Ce) films and enhancing their growth. Both types of LbL films are based on reversible coordinative bonding between the metal ions and the oxygen-bearing groups in PP and GO, instead of purely electrostatic interactions. The GO incorporation leads to the doubling of the areal mass density and to a dry film thickness close to 300 nm after 4 (GO/Ce/PP/Ce) tetralayers. The film roughness increases significantly with thickness. The (PP/Ce) films are soft materials with approximately equal shear storage and loss moduli, but the incorporation of GO doubles the storage modulus. PP displays a marked terminating layer effect and practically eliminates mechanical losses, making the (GO/Ce/PP/Ce) films almost pure soft elastomers. The smoothness of the (PP/Ce) films and the PP-termination effects are attributed to the reversible coordinative bonding. The (GO/Ce/PP/Ce) films oxidize pyrrole and 3,4-ethylenedioxythiophene (EDOT) and form polypyrrole and PEDOT films on their surfaces. These polymer films are considerably thicker than those formed using the (PP/Ce) multilayers with the same nominal amount of cerium layers. The GO sheets interfere with the polymerization reaction and make its kinetics biphasic. The (GO/Ce) multilayers without PP are brittle and thin.

Synthesis of a metal-coordinated N-substituted polybenzimidazole pyridine sulfone and method for the nondestructive analysis of thermal stability

N-substituted metal-coordinated cross-linking polybenzimidazole pyridine sulfone, as novel class of high-performance functional polymers, has been obtained by the coordination of N-substituted polybenzimidazole pyridine sulfone (Py-N-PBIS) ligand with varying content of metallic ion (Co2+, Ni2+, Zn2+). The structures of the polymers are characterized by means of fourier transform infrared spectroscopy (FT-IR) and 1H nuclear magnetic resonance (1H NMR) spectroscopy, the results show good agreement with the proposed structures. Thermogravimetric analysis measurements exhibit that the metal coordination polymers possess good thermal stability with high thermal decomposition temperature (thermally stable up to 405–510°C). More importantly, the thermal decomposition temperature of Py-N-PBIS-(Co2+, Ni2+, Zn2+) can be nondestructively detected by taking advantage of the fluorescence quenching effect of metal coordination to 2,6-Bis(2-benzimidazolyl)pyridine structure.

Metal-coordination crosslinked N-polyindoles as recyclable high-performance thermosets and nondestructive detection for their tensile strength and glass transition temperature

Metal coordination crosslinking between stiff N-polyindole chains was constructed, and the crosslinked films exhibited high tensile strength, high heat resistance and excellent polar solvent resistance.

Facile synthesis of recyclable Zn(ii)-metallosupramolecular polymers and the visual detection of tensile strength and glass transition temperature

A series of recyclable crosslinked Zn(ii)-metallosupramolecular coordination polymers are successfully achieved, of which tensile strength and T_g could be visually detected.

Seawater-Assisted Self-Healing of Catechol Polymers via Hydrogen Bonding and Coordination Interactions

It is highly desirable to prevent crack formation in polymeric materials at an early stage and to extend their lifespan, particularly when repairs to these materials would be difficult for humans. Here, we designed and synthesized catechol-functionalized polymers that can self-heal in seawater through hydrogen bonding and coordination. These bioinspired acrylate polymers are originally viscous materials, but after coordination with environmentally safe, common metal cations in seawater, namely, Ca(2+) and Mg(2+), the mechanical properties of the polymers were greatly enhanced from viscous to tough, hard materials. Reduced swelling in seawater compared with deionized water owing to the higher osmotic pressure resulted in greater toughness (∼5 MPa) and self-healing efficiencies (∼80%).

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.

Tunable luminescence of lanthanide (Ln = Sm, Eu, Tb) hydrophilic ionic polymers based on poly(N-methyl-4-vinylpyridinium-co-styrene) cations

Hydrophilic luminescent lanthanide-containing ionic polymers poly-[MVPS]₂[Ln(NO₃)₅] were prepared, which can be utilized as reversible colorimetric water-responsive sensors.

Directional supracolloidal self-assembly via dynamic covalent bonds and metal coordination

An emerging strategy towards the sophistication of supramolecular nanomaterials is the use of supracolloidal self-assembly, in which micelles or colloids are used as building blocks. Binding directionality can produce nanostructures with attractive properties. Herein, we present a new directional supracolloidal self-assembly by virtue of dynamic covalent bonds and metal coordination in water. Conjugation of a ligand precursor to a water-soluble block copolymer through dynamic covalent bonds leads to the dehydration and micellization of the functionalized polymer. Reversible reaction facilitates the permeation of metal ions into core-shell interfaces. Conversely, metal-coordination promotes reaction over the interfaces. Cu(ii)-coordination occurs overwhelmingly inside each isolated micelle. However, Zn(ii)-coordination induced a directional self-assembly whose nanostructures evolve stepwise from nanorods, nanowires, necklaces, and finally to supracolloidal networks scaling-up to several tens of micrometres. Post-reactions of simultaneous dynamic covalent bond conversion and Zn(ii)-coordination over the core-shell interfaces endow these supracolloidal networks with a huge specific surface area for hydrophobic dative metal centres accessible to substrates in water. Water-soluble shells play important roles in directional supracolloidal assembly and in the stabilization of nanostructures. Thus the directional self-assembly provides a versatile platform to produce metallo-hybridized nanomaterials that are promising as enzyme-inspired aqueous catalysts.

Revealing the supramolecular nature of side-chain terpyridine-functionalized polymer networks

Nowadays, finely controlling the mechanical properties of polymeric materials is possible by incorporating supramolecular motifs into their architecture. In this context, the synthesis of a side-chain terpyridine-functionalized poly(2-(dimethylamino)ethyl methacrylate) is reported via reversible addition-fragmentation chain transfer polymerization. By addition of transition metal ions, concentrated aqueous solutions of this polymer turn into metallo-supramolecular hydrogels whose dynamic mechanical properties are investigated by rotational rheometry. Hence, the possibility for the material to relax mechanical constrains via dissociation of transient cross-links is brought into light. In addition, the complex phenomena occurring under large oscillatory shear are interpreted in the context of transient networks.

Thermal-healable and shape memory metallosupramolecular poly(n-butyl acrylate-co-methyl methacrylate) materials

Thermal-induced shape memory and healing based on a metallosupramolecular polymer were realized.

Nonlinear mechanics of thermoreversibly associating dendrimer glasses

We model the mechanics of associating trivalent dendrimer network glasses with a focus on their energy dissipation properties. Various combinations of sticky bond (SB) strength and kinetics are employed. The toughness (work to fracture) of these systems displays a surprising deformation-protocol dependence; different association parameters optimize different properties. In particular, "strong, slow" SBs optimize strength, while "weak, fast" SBs optimize ductility via self-healing during deformation. We relate these observations to breaking, reformation, and partner switching of SBs during deformation. These studies point the way to creating associating-polymer network glasses with tailorable mechanical properties.