Supramolecular Polymer Networks Research Articles

Glycoluril Clips for the Construction of Chemoresponsive Supramolecular Polymer Networks through Homodimer Cross-Links.

The formation of polymer supramolecular networks exhibiting selective sensitivity toward a narrow class of organic compounds is still a significant challenge within the area of reversibly cross-linked materials. Glycoluril molecular clips are U-shaped molecules, which, besides the ability to undergo self-sorting homodimerization, exhibit selectively high molecular recognition of dihydroxyaromatic species. A glycoluril clip diol was introduced into a polymer backbone by using standard polyurethane chemistry. Immobilization of the molecular clip along the polyurethane macromolecule (Glyc Clip-polyurethane) was shown to preserve the native association properties of the clip. Clip motifs embedded in macromolecules form homodimer cross-links in CHCl3 and the resulting structures have a thermoresponsive character. The strength of homodimerization Khomodimer varies from 7.74 104 l mol-1 at 265 K to 9.47 102 l mol-1 at 315 K. A 30 wt % solution of Glyc Clip-polyurethane undergoes gelation at room temperature and exhibits a constant elastic modulus, approximately 3.1 ⋅ 104 Pa, in the broad investigated frequency range. The obtained organogels exhibit selective chemoresponsive properties in the presence of resorcinol, which was demonstrated with 1 H high-resolution magic-angle-spinning NMR spectroscopy and rheological measurements.

Aggregation-Induced Emission Supramolecular Organic Framework (AIE SOF) Gels Constructed from Supramolecular Polymer Networks Based on Tripodal Pillar[5]arene for Fluorescence Detection and Efficient Removal of Various Analytes

Herein, an aggregation-induced emission (AIE) supramolecular organic framework gel (SOF-TPN-G) was successfully constructed from novel supramolecular polymer networks based on tripodal pillar[5]are...

Bonding and Debonding on Demand with Temperature and Light Responsive Supramolecular Polymers

AbstractDue to their low melt viscosity, competitive adhesive properties, and the stimuli‐responsive nature of supramolecular interactions, various supramolecular polymers have recently been investigated as adhesives with on‐demand (de)bonding capability. The adhesive properties of a series of hydrogen‐bonded supramolecular polymer networks based on a telechelic poly(ethylene‐co‐butylene) (PEB) terminated with isophthalic acid (IPA) groups and a series of bifunctional pyridines (Py) are reported herein. These supramolecular polymers microphase segregate into an IPA‐Py rich hard phase and an amorphous low‐glass‐transition PEB phase, and their properties depend on the nature of the pyridine‐carrying monomer. Rheological measurements show that the polymers disassemble into low‐viscosity melts when heated above the melting or glass transition temperature of the hard phase. Lap joints bonded with the polymers display a shear strength of up to 1.3 MPa, and debonding is possible in less than 10 s upon heating or exposure to UV–light; to enable rapid light‐induced (de)bonding, a light–heat converter is introduced. Cyclic bonding/debonding experiments reveal that the shear strength remains unchanged over five cycles and demonstrate that the process is very robust.

Construction of anion‐responsive crosslinked polypseudorotaxane based on molecular recognition of pillar[5]arene

ABSTRACTA pillar[5]arene pendant polymer (Poly‐P[5]A) is synthesized via ROMP using Grubb's first‐generation catalyst. GPC analysis of the polymer suggested ~30 pendant pillar[5]arene units in the polymer. Supramolecular polypseudorotaxane assembly is constructed by intermolecularly crosslinking pendant pillar[5]arene units using a bispyridinium guest via host–guest complexation. Formation of the polypseudorotaxane assembly is characterized by 1D/2D NMR techniques and DLS analysis. Moreover, anion‐responsiveness of the polypseudorotaxane assembly is demonstrated by 1H NMR spectroscopic analysis using chloride anion as external stimulus. Scanning electron microscopic analysis of the poly‐P[5]A showed breath‐figure assembly and upon crosslinking with G.2PF6 the polymer self‐assemble to give a supramolecular polymer network. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1508–1515

(Invited) visco-Poroelastic & Iontronic Pump: New Strategy for Ultrasensitive Artificial Skin Sensors

Creating artificial sensor skins that shows the tactile- and chemical-sensing capability of human skin has been a big challenge in wearable sensor research. In particular, biomimetics has emerged as a burgeoning area in the field of deformable tactile sensor skins that has led innovations in material designing and device structure manipulation with the aim of imitating multimodal sensing features of human skin intelligently. Herein, inspired by the sophisticated physiological sensing mechanism of living cells, we describe a uniquely designed visco-poroelastic, iontronic pump consisting of artificial ions confined into polymeric network matrix or well-designed hybrid interface. Novel bottom-up strategy employed here resulted into supramolecular polymer networks through non-covalent interactions between poroelastic artificial ions and viscoelastic polymer chains, which endows effective iontronic pumping under mechanical stimuli and electronic field, simultaneously. This design for visco-poroelastic, iontronic, and ion confined artificial mechanoreceptors allows for ultrasensitive mechanosensing over a wide spectrum of pressure (Pa~150kPa) beyond capabilities of human skin. Moreover, our devices could visualize the local variation in the applied pressure or electronic field without using spatially distributed device arrays.

Dynamics of Supramolecular Self-Healing Recovery in Extension

Self-healing materials are prized for their ability to recover mechanical properties after damage. Supramolecular polymer networks have been demonstrated to have the ability to recover without the need for extraneous material components or the use of external stimuli. Surprisingly, there is little quantitative measure of self-healing dynamics and recovery. In this work, we develop a tool using a filament stretching rheometer to probe self-healing dynamics in creep and constant rate of extension. We experimentally determine the effect of process time scales, τH and τW, on the degree of recovery for two distinct supramolecular architectures. These results are put into the context of molecular time scales such as disengagement time, the Rouse time, and bond lifetime. We find that entangled polymers undergo sequential healing, whereby at short times, dynamics are dominated by entanglement recovery followed by recovery of associations. For an unentangled polymer, recovery is seemingly dominated by association ...

Dynamics of supramolecular associative polymer networks at the interplay of chain entanglement, transient chain association, and chain‐sticker clustering

ABSTRACTThe dynamic mechanical properties of supramolecular associative polymer networks depend on the average number of entanglements along the network‐forming chains, Ne, and on their content of associative groups, f. In addition, there may be further influence by aggregation of the associative groups into clusters, which, in turn, is influenced by the chemical structure of these groups, and again by Ne and f of the polymer. Therefore, the effects of these parameters are interdependent. To conceptually understand this interdependency, we study model networks in which (a) Ne, (b) f, and (c) the chemical structure of the associative groups are varied systematically. Each network is probed by rheology. The clustering of the associative groups is assessed by analyzing the rheological data at the end range of frequency covered and by comparison of the number of supramolecular network junctions with the maximum possible number of binary transient bonds. We find that if the total number of the network junctions, which can be formed either by interchain entanglement or by interchain transient associations, is greater than a threshold of 13, then the likelihood of cluster formation is high and the dynamics of supramolecular associative polymer networks is mainly controlled by this phenomenon. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1209–1223

Local dynamics in supramolecular polymer networks probed by magnetic particle nanorheology.

Transient supramolecular polymer networks are promising candidates as soft self-healing or stimuli-sensitive materials. In this paper, we employ a novel nanorheological approach, magnetic particle nanorheology (MPN), in order to better understand the local dynamic properties of model supramolecular networks from a molecular point of view. Hence, the bond strength between four-arm star-shaped polyethylene glycol (PEG) functionalized at the four extremities with terpyridine ligands is tuned by implementing different metal ions with variable complexation affinities for the ligand. We show that MNP allows for the evaluation of the strength and connectivity of the polymer networks by the estimation of relaxation times, mesh size, and also the viscoelastic properties of these materials. These results are compared and complemented to former outcomes on these systems that were obtained by macroscopic analytical methods. A clear dependence between the strength of the metal-ligand complex and the local dynamics of the polymeric network is observed by the nanorheological approach, which is in good agreement with previous predictions related to the complex formation constants.

Construction and morphology of non-covalently double-crosslinked supramolecular polymer networks

A straightforward synthesis of α-Ba, ω-TAP functionalized polymers, Ba-PnBuA-TAP, is reported, leading to the formation of double-crosslinked supramolecular networks driven via the sequential hydrogen-bonding association and metal-coordination.

Self-assembly of supramolecular polymers in water from tetracationic and tetraanionic monomers in water through cooperative electrostatic attraction and aromatic stacking

The cooperative electrostatic attraction and π-π aromatic stacking interactions between tetrahedral tetrapyridinium TP and three tetraanionic tetraphenylethylene derivatives TPE-1∼3 led to the formation of a new kind of supramolecular polymer networks in water, which have been confirmed by 1H NMR, fluorescence, isothermal titration calorimetric (ITC) and dynamic light scattering (DLS) experiments. ITC studies show that the contributions of enthalpy and entropy were comparable, reflecting the importance of hydrophobicity in driving the intermolecular aromatic stacking. DLS experiments indicate that the linear supramolecular polymers formed by these tetratopic monomers further aggregated into networks of 102-nm size.

Construction of Metallacage-Cored Supramolecular Gel by Hierarchical Self-Assembly of Metal Coordination and Pillar[5]arene-Based Host-Guest Recognition.

In this work, a Pd2 L4 metallacage 2•([BF4 ]- )4 with four pillar[5]arene units is first prepared and characterized by 1D multinuclear NMR (1 H, 11 B, and 19 F NMR), 2D 1 H-1 H correlation spectra, 1 H-13 C heteronuclear single quantum coherence, and diffusion-ordered NMR spectroscopy, and electrospray ionization time-of-flight mass spectrometry. By the introduction of a ditopic guest molecule 3 into a chloroform solution of 2•([BF4 ]- )4 , a supramolecular polymer network gel is successfully constructed based on the metal coordination interactions and host-guest recognition between the pillar[5]arene units of 2•([BF4 ]- )4 and neutral ditopic guest molecule 3. The temperature and pH responsivenesses of the supramolecular gel are studied, which are further employed for the controlled release of different cargos. As a demonstration, emodin and methylene blue are trapped in the cavities of the metallacage and in the pores of the supramolecular gel, respectively. Methylene blue is first released along with the gel-sol transition while emodin is then released by the further addition of acid to destroy the metallacage. This study explores the use of metallacage-cored supramolecular network gels for sequential controlled release and contributes to the development of smart and adaptive materials.

Modulation of Supramolecular Interactions of Urea-based Supramolecular Polymers via Molecular Structures

Linear bis-urea D230 series and branched tris-urea T403 series of supramolecular monomers were synthesized using low molecular weight polyetheramine D230, T403 and isocyanates with diverse functional groups. Rheological tests reveal that the materials possess special thermal and mechanical properties due to the strong hydrogen bonding interactions between terminal urea groups and the high flexibility of the polyetheramine middle segments. By enhancing the hydrogen bonding interactions through electronic effects of the substituted urea groups, the mechanical properties of the bulk material can be increased. Moreover, the branched T403 series with higher hydrogen bonding density also shows better performance against D230 series with the same substituted urea groups. The presence of π-π stacking between the phenyl groups in samples with phenylurea residues, which complements the hydrogen bonding, was also confirmed by fluorescence spectroscopy, therefore resulting in a stronger supramolecular polymer network.

Nanoparticles from supramolecular polylactides overcome drug resistance of cancer cells

A major drawback of chemotherapy is that cancer cells can develop multi-drug resistance, leading to failure of anticancer treatments. To overcome this limitation, we report the preparation of environment-sensitive polylactide (PLA)-based nanoparticles, assembled by multiple hydrogen bonds. These nanoparticles showed sizes in the 100–150 nm range, a spherical morphology, and low toxicity in cell culture. In addition, their 3D supramolecular polymer network was sensitive to both pH and temperature and yielded dynamically reversible networks that could recognize the intrinsic differences between cancer and normal tissues. Release studies of the encapsulated anticancer drug doxorubicin (DOX) demonstrated that the nanoparticles exhibited high stability at physiological conditions. However, when the pH was reduced from 7.4 to 5, an accelerated release was observed. Most importantly, by applying this supramolecular linked nanocarrier for the delivery of DOX, the drug-resistance of KB-V1 cells could be overcome. All these features demonstrate the versatility of the proposed modular approach and their great potential for anticancer therapy.

Strategy for Constructing Shape-Memory Dynamic Networks through Charge-Transfer Interactions.

Recently, charge transfer (CT) interactions have received attention for the fabrication of supramolecular architectures due to their inherent compatibilities, directional nature and solvent tolerance. In this study, we report a shape-memory dynamic network constructed by the CT interaction between π-electron-rich naphthalene embedded in poly(ethylene glycol) (PEG-Np) and π-electron-poor six-arm methyl-viologen-ended poly(ethylene glycol) (6PEG-MV), which was verified by ultraviolet-visible spectroscopy (UV-vis), fluorescence spectra and swelling tests. Interestingly, the mechanical properties of this CT complex were dramatically enhanced compared with the control without CT interaction. Moreover, the excellent shape-memory effect (SME) was realized due to the good crystallization of the PEG segment and stable netpoints based on the CT interaction. In addition, as we expected, this supramolecular polymer network is self-healable and reprocessable.

Fluorescent Metallacage-Core Supramolecular Polymer Gel Formed by Orthogonal Metal Coordination and Host-Guest Interactions.

Herein, we report the preparation of a multifunctional metallacage-core supramolecular gel by orthogonal metal coordination and host-guest interactions. A tetragonal prismatic cage with four appended 21-crown-7 (21C7) moieties in its pillar parts was first prepared via the metal-coordination-driven self-assembly of cis-Pt(PEt3)2(OTf)2, tetraphenylethene (TPE)-based sodium benzoate ligands and linear dipyridyl ligands. Further addition of a bisammonium linker to the cage delivered a supramolecular polymer network via the host-guest interactions between the 21C7 moieties and ammonium salts, which formed a supramolecular gel at relatively higher concentrations. Due to the incorporation of a TPE derivative as the fluorophore, the gel shows emission properties. Multiple stimuli responsiveness and good self-healing properties were also observed because of the dynamic metal coordination and host-guest interactions used to stabilize the whole network structure. Moreover, the storage and loss moduli of the gel are 10-fold those of the gel without the metallacage cores, indicating that the rigid metallacage plays a significant role in enhancing the stiffness of the gel. The studies described herein not only enrich the functionalization of fluorescent metallacages via elegant ligand design but also provide a way to prepare stimuli-responsive and self-healing supramolecular gels as robust and smart materials.

Dominance of Chain Entanglement over Transient Sticking on Chain Dynamics in Hydrogen-Bonded Supramolecular Polymer Networks in the Melt

The chain dynamics in supramolecular polymer networks is determined by the interplay of the kinetics of transient interchain association and relaxation of the network chains themselves. This interplay can be addressed by studying model supramolecular polymer networks in which the number of associative side groups and the molar mass of the covalently jointed backbone polymers are both varied systematically. To realize this idea, we use precursor chains with three different molar masses, which comes along with different extents of entanglement in the melt state. For each molar mass, the precursor polymers are functionalized with three different relative contents of associative side groups, giving rise to transient network formation in the melt state. We evaluate the chain dynamics in these transient networks by probing the diffusivity of fluorescently labeled tracer chains by fluorescence recovery after photobleaching (FRAP). In these studies, we find that the presence of entanglements markedly outweighs the influence of transient associative interactions.

Thermal and viscoelastic properties of entangled supramolecular polymer networks as a powerful tool for prediction of their microstructure

Thermal and viscoelastic properties of entangled supramolecular polymer networks, SPNs, depend strongly on binary and collective assembly of associative groups. The collective assemblies can phase separate from polymer matrix chains and form domains with different sizes and shapes, which have different melting point transitions. By increasing content of associative groups along the polymer chains, their high-order association leads to formation of domains, which have higher melting temperatures than other ones. We prepared a SPN system that contains three networks. All networks have similar precursor polymer backbone, but different content of ureidopyrimidinone, UPy, moiety as strong hydrogen bonding associative group. Thermal and viscoelastic properties of these networks were studied by differential scanning calorimetry and dynamic mechanical thermal analysis measurements. Binary-associated UPy groups phase separate into collective assemblies by π–π stacking. These stacks melt at different temperatures upon heating. The presence of transient assemblies is considerably hinder the relaxation of polymer backbone chains. These domains can be observed in the microstructure of networks by optical microscopy. Thermal and viscoelastic properties of sample with highest content of UPy groups are significantly different from the other networks. This is related to the high-order association of UPy motifs, as can be captured by presence of needle-like domains in its microstructure.

An AIEE fluorescent supramolecular cross-linked polymer network based on pillar[5]arene host–guest recognition: construction and application in explosive detection

Here a novel fluorescent supramolecular cross-linked polymer network with aggregation induced enhanced emission (AIEE) properties was constructed via pillar[5]arene-based host-guest recognition. Furthermore, the supramolecular polymer network can be used for explosive detection in both solution and thin films.

Secondary dialkylammonium salt/crown ether [2]pseudorotaxanes as nanostructured platforms for proton transport.

Multivalent secondary dialkylammonium salt/crown ether [2]pseudorotaxane, supramolecular polymer networks have been obtained by mixing surfactant-encapsulated clusters with dibenzo[24]crown-8 groups and star polymers end functionalized with dibenzylammonium ions. This induces remarkable enhancements and rational control of proton conductivity of the supramolecular networks.

A novel supramolecular polymer network based on a catenane-type crosslinker

A novel supramolecular mechanically interlocked crosslinker was designed and used to prepare a supramolecular polymer network.