Supramolecular Polymer Gel Research Articles

Gels based on anion recognition between triurea receptor and phosphate anion.

Anion recognition between the triurea receptor and phosphate anion is demonstrated as the cross-linkage to build supramolecular polymer gels for the first time. A novel multi-block copolymer (3) is designed to have functional triurea groups as cross-linking units along the polymer main chain. By virtue of anion coordination between the triurea receptor and phosphate anion with a binding mode of 2:1, supramolecular polymer gels are then prepared based on anion recognition using 3 as the building block.

A novel supramolecular polymer gel constructed by crosslinking pillar[5]arene-based supramolecular polymers through metal–ligand interactions

A novel heteroditopic A-B monomer was synthesized and used to construct linear supramolecular polymers utilizing pillar[5]arene-based host-guest interactions. Specifically, upon addition of Cu(2+) ions, the supramolecular polymer chains are crosslinked through metal-ligand interactions, resulting in the formation of a supramolecular polymer gel. Interestingly, this self-organized supramolecular polymer can be used as a novel fluorescent sensor for detecting Cu(2+) ions.

A double supramolecular crosslinked polymer gel exhibiting macroscale expansion and contraction behavior and multistimuli responsiveness

Here we report a novel supramolecular polymer gel containing two types of physical crosslinks that are orthogonal to each other. It shows macroscale expansion and contraction behavior and multistimuli responsiveness.

Copillar[5]arene-based supramolecular polymer gel: controlling stimuli–response properties through a novel strategy with surfactant

Cartoon representation of self-assembly pathway of gelator DCP5-16 with G in CD3CN.

A multiple-responsive self-healing supramolecular polymer gel network based on multiple orthogonal interactions.

Supramolecular polymer networks have attracted considerable attention not only due to their topological importance but also because they can show some fantastic properties such as stimuli-responsiveness and self-healing. Although various supramolecular networks are constructed by supramolecular chemists based on different non-covalent interactions, supramolecular polymer networks based on multiple orthogonal interactions are still rare. Here, a supramolecular polymer network is presented on the basis of the host-guest interactions between dibenzo-24-crown-8 (DB24C8) and dibenzylammonium salts (DBAS), the metal-ligand coordination interactions between terpyridine and Zn(OTf)2 , and between 1,2,3-triazole and PdCl2 (PhCN)2 . The topology of the networks can be easily tuned from monomer to main-chain supramolecular polymer and then to the supramolecular networks. This process is well studied by various characterization methods such as (1) H NMR, UV-vis, DOSY, viscosity, and rheological measurements. More importantly, a supramolecular gel is obtained at high concentrations of the supramolecular networks, which demonstrates both stimuli-responsiveness and self-healing properties.

Copillar[5]arene-based supramolecular polymer gels

Copillar[5]arene-based supramolecular polymer gels were obtained in acetonitrile. These supramolecular polymer gels were driven by C–H⋯π interactions, presented two phases as time goes on, and finally formed a supramolecular organic framework. Notably, the supramolecular polymer gels showed reversible gel–sol phase transitions upon heating and cooling. Moreover, the gels exhibit excellent self-healing properties.

Supramolecular polymer gels formed from carboxy-terminated telechelic polybutadiene and polyamidine through amidinium-carboxylate salt bridge

In this article, we report the preparation and properties of the bulk supramolecular polymer gels prepared from a polybutadiene based on the amidinium-carboxylate salt bridge, highlighting the difference from a well-established network system based on carboxylic acid and amine. We have prepared the amidinium-carboxylate salt bridge-based supramolecular polymer gels from a carboxy-terminated telechelic polybutadiene and a linear polyamidine having N,N′-di-substituted acetamidine group in the main chain. FTIR analysis along with Small angle X-ray scattering measurements indicated that the salt bridge was attributed to the gelation through three-dimensional network formation. Virtually no fluidity was observed for the supramolecular gel containing equimolar amounts of the carboxyl group and the amidine group, which showed a high G′ value of about 1 MPa at room temperature and a Tgel of 37 °C. For comparison, the supramolecular polymer gels crosslinked by ammonium-carboxylate salt were prepared using a linear polyethyleneimine instead of the polyamidine. The gel with equimolar amounts of the carboxyl group and the secondary amino group showed liquid-like fluidity with a G′ value of about 0.01 MPa at room temperature, which was attributed to the fact that a certain amount of the carboxyl group remained as its free form without salt formation, as evidenced by FTIR analysis. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1815–1824

Cross-Linked Supramolecular Polymer Gels Constructed from Discrete Multi-pillar[5]arene Metallacycles and Their Multiple Stimuli-Responsive Behavior

A new family of discrete hexakis-pillar[5]arene metallacycles with different sizes have been successfully prepared via coordination-driven self-assembly, which presented very few successful examples of preparation of discrete multiple pillar[n]arene derivatives. These newly designed hexakis-pillar[5]arene metallacycles were well characterized with one-dimensional (1-D) multinuclear NMR ((1)H and (31) P NMR), two-dimensional (2-D) (1)H-(1)H COSY and NOESY, ESI-TOF-MS, elemental analysis, and PM6 semiempirical molecular orbital methods. Furthermore, the host-guest complexation of such hexakis-pillar[5]arene hosts with a series of different neutral ditopic guests G1-6 were well investigated. Through host-guest interactions of hexakis-pillar[5]arene metallacycles H2 or H3 with the neutral dinitrile guest G5, the cross-linked supramolecular polymers H2⊃(G5)3 or H3⊃(G5)3 were successfully constructed at the high-concentration region, respectively. Interestingly, these cross-linked supramolecular polymers transformed into the stable supramolecular gels upon increasing the concentrations to a relatively high level. More importantly, by taking advantage of the dynamic nature of metal-ligand bonds and host-guest interactions, the reversible multiple stimuli-responsive gel-sol phase transitions of such polymer gels were successfully realized under different stimuli, such as temperature, halide, and competitive guest, etc. The mechanism of such multiple stimuli-responsive processes was well illustrated by in situ multinuclear NMR investigation. This research not only provides a highly efficient approach to the preparation of discrete multiple pillar[n]arene derivatives but also presents a new family of multiple stimuli-responsive "smart" soft matters.

A supramolecular polymer gel with dual-responsiveness constructed by crown ether based molecular recognition

A supramolecular polymer gel was prepared from self-assembly of a heteroditopic A–B monomer based on benzo[18]crown-6. Such a gel shows interesting gel–sol transitions in response to dual-stimuli owing to the dynamically reversible complexation between benzo[18]crown-6 and primary alkylammonium salt moieties.

Rapid self-healing and triple stimuli responsiveness of a supramolecular polymer gel based on boron–catechol interactions in a novel water-soluble mussel-inspired copolymer

Marine and freshwater mussels secrete proteinaceous adhesive materials for adherence to the substrates upon which they reside. It is well known that 3,4-dihydroxyphenylalanine (DOPA) is the key to understanding these mussel adhesive proteins (MAPs). In order to gain a better understanding of their complex formation and quick recovery upon rupturing, novel water soluble copolymers of N-isopropylacrylamide and dopamine methacrylate were synthesized in such a way that they have 1, 2.5, and 5 mole percent dopamine monomer with respect to the NIPAM monomer on average. The statistical distribution of DOPA-functionalities along the chain makes the material a close synthetic equivalent of the byssal thread proteins of mytili. At acidic pH, the aqueous copolymer solution behaves like an unentangled copolymer solution, but at basic pH, these catechol functionalities form a dicomplex with H3BO3, thereby crosslinking two chains, proven by 11B-NMR and gelation. The polymer solution is thermosensitive with a pH-dependent lower critical solution temperature (LCST) between 21 and 33 °C, depending on the DOPA-content. If 2 or more functionalities per chain are present, a gel is formed that is self-healing with very quick recovery from sustained damage. The moduli of the gels depend on the concentration of functionalities. Hence, triple stimuli responsive copolymers were obtained.

Supramolecular polymer gel with multi stimuli responsive, self-healing and erasable properties generated by host–guest interactions

A supramolecular polymer gel formed between triptycene-based bis(crown ether) and copolymer containing dibenzylammonium (DBA) moieties by host–guest interactions was described. We demonstrated the formation of the supramolecular polymer networks between the bis(crown ether) and the copolymer by the 1H NMR spectroscopy and solution viscometry, and we also obtained a colorless and transparent supramolecular polymer gel at high concentration. Moreover, the supramolecular polymer gel showed multi-stimuli reversible responsiveness, such as thermo-, acid/base-, and chemo- induced gel–sol transitions. Furthermore, the result of rheological measurements showed the gel has an intrinsic self-healing property, and the thixotropic process could be repeated at least three times. Interestingly, when doped with spiropyran molecules, the supramolecular polymer gel could also be employed as erasable materials. Thus, these results could be highly anticipated to benefit for further construction of smart materials with high healing efficiency, and ultimately be used in practical application.

Thermoreversible Supramolecular Polymer Gels via Metal–Ligand Coordination in an Ionic Liquid

Thermoreversible supramolecular polymer gels were prepared via metal–ligand coordination by mixing a poly(4-vinylpyridine)-b-poly(ethyl acrylate)-b-poly(4-vinylpyridine) (P4VP–PEA–P4VP) triblock copolymer and zinc chloride (ZnCl2) in a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imidide. FT-IR spectroscopy revealed metal–ligand coordination between zinc in ZnCl2 and pyridine groups as ligands on P4VP blocks, even in an ionic liquid. Thermoreversible viscoelastic properties between a semisolid (gel-like) state and a liquid-like state were confirmed by temperature-ramp oscillatory shear measurements. It was also revealed that thermoreversibility of supramolecular polymer gels depended strongly on stoichiometry between ligands and metals, where the maximum of storage modulus-loss modulus crossover temperature (Tgel) as an indicator of gelation was achieved when a molar amount of available coordination sites was a certain excessive amount (coordination site/ligand ratio ∼1.6). The molar ratio at the maximum Tgel is nearly independent of the number of ligands per triblock copolymer. On the other hand, the number of ligands per triblock copolymer affected the Tgel, where a larger number of ligands per triblock copolymer gave a higher Tgel, regardless of almost the same molecular weight of triblock copolymers.

A Stimulus‐Response and Self‐Healing Supramolecular Polymer Gel Based on Host–Guest Interactions

AbstractA supramolecular polymer gel is formed by host‐guest interactions between a DB24C8‐based bis(crown ether) and a copolymer containing the dibenzylammonium moiety. The formation of the gel and its cross‐linked networks structure are evidenced by 1H NMR spectroscopy, viscometry, and SEM. Interestingly, the gel shows both pH‐ and thermoesponsive behaviors, and excellent self‐healing properties. The self‐healing property of the gel is tested by rheological measurements, and it can also be seen visually and directly. The presented work provides a new strategy for the construction of the self‐healing supramolecular polymer gels with potential applications in smart materials.magnified image

Cross-linked supramolecular polymer networks with responsive and elastic gel properties via host–guest complexation: controlled release of squaraine dyes

Triptycene-derived macrotricyclic polyether was proved to be an efficient “molecular glue” for cross-linking the copolymer containing dibenzylammonium salts to form supramolecular polymer networks via host–guest complexation, which was evidenced by 1H NMR spectroscopy, solution viscometry, and formation of transparent and elastic supramolecular polymer gels. Interestingly, a well-defined porous structure of the supramolecular polymer gel could be observed at the fully cross-linked density, and its mechanical properties could be modulated by the amount of the macrotricyclic host added to the system. Moreover, the supramolecular polymer gel showed acid/base- and thermo-induced reversible gel–sol transitions. Additionally, the supramolecular polymer gel could also be employed for the encapsulation and controllable release of squaraine dyes, which might find potential applications in materials science.

A modular construction kit for supramolecular polymer gels

Supramolecular polymer gels are swollen networks of macromolecules interconnected by transient, non-covalent bonds; they form an extraordinarily useful class of soft, stimuli-sensitive materials. To optimize the use of supramolecular polymer gels in applications, their physical and chemical properties must be understood. This understanding is ideally achieved using model systems that allow the type and strength of supramolecular chain crosslinking to be varied to a great extent without concurrent alteration of the properties of the covalent polymer backbones. We introduce a system that provides these requirements. We use linear chains of electrophilic methacryl-succinimidyl (MASI) modified poly(N-isopropylacrylamide) (pNIPAAm). These polymers can be modified in a modular fashion by replacing their electrophilic MASI units by nucleophilic amine-functionalized derivatives of custom, supramolecular crosslinkable functionalities. We follow this approach and prepare a set of pNIPAAm polymers that consist of exactly the same polymer backbone functionalized with different types of crosslinkable sidegroups. These polymers are then crosslinked by addition of low molecular weight linkers that are complementary to the motifs on the polymer. We use multiple hydrogen bonding based on diaminotriazine and maleimide, cyanuric acid and Hamilton wedges, and diaminotriazine and cyanuric acid; we also use metal complexation based on terpyridine and different metal salts. This approach creates supramolecular networks of greatly varying rheological properties, from low viscous liquids to elastic gels, each showing consistent and quantitative correlation between the gel mechanical properties and the binding strength of the respective constituent supramolecular crosslinking motifs. Exploiting the good solubility of the common pNIPAAm backbone polymer in a variety of solvents allows these networks to be prepared and studied in different media with unprecedented consistency and flexibility.

A self-healing supramolecular polymer gel with stimuli-responsiveness constructed by crown ether based molecular recognition

A cross-linked supramolecular polymer network gel was prepared by orthogonal self-assembly of two homoditopic monomers and a metallic cross-linker. The gel is transparent and free-standing, which not only shows an interesting gel–sol transition in response to quadruple-stimuli, but also exhibits self-healing properties, as can be seen by the naked eye and as evidenced by rheological characterization. These unique features are all due to the dynamically reversible host–guest complexation and good mechanical properties of the cross-linked polymer network. Therefore, these fascinating properties make this supramolecular gel an unprecedentedly intelligent material.

A Supramolecular Polymer Blend Containing Two Different Supramolecular Polymers through Self‐Sorting Organization of Two Heteroditopic Monomers

The creation of complex and highly-ordered structures with desired properties and novel functions has been fundamental to supramolecular chemistry and material science, and plays an essential role in high-tech and biorelated fields, such as drug delivery systems, molecular devices and photovoltaic applications. Nature, as the best example of precise and efficient self-assembly processes, promotes chemists to engage in developing highly-ordered artificial supramolecular assemblies, such as supramolecular polymers through the utilization of noncovalent interactions. Held together by reversible and highly dimensional interactions, such as host–guest interactions, hydrogen bonds, and metal coordination, supramolecular polymers have become one of the most active frontiers in the past two decades and have received a great deal of attention. Compared with conventional polymers, supramolecular polymers typically show many dynamic or precisely controllable properties arising from dynamic linking between the constituent monomers and have the ability to respond to their environment as adaptive materials. The interest in supramolecular polymers has expanded in recent years, not only for their potential properties as functional materials, but also for their intriguing architectures and topologies that act as a basic aspect of potential applications. The simple blending of different polymers has produced new polymer blend materials with controllable and unique properties. Polymer blends have been widely studied in polymer chemistry and materials science, and as such supramolecular polymer blends, defined as mixtures of two or more different and mutually exclusive supramolecular polymers, are an attractive topic. There are beautiful examples of miscible polymer blends based on either multiple hydrogen-bonding, p-stacking, carboxy–amine interactions, or crown ether functionlized polymers with ammoniumor paraquat-functionalized polymers. However, these blends were composed of high-molecular-weight, conventional covalently bonded polymers instead of noncovalently connected supramolecular polymers. It is still a big challenge for chemists to design and prepare supramolecular polymer blends completely from low-molecularweight monomers without any conventional polymeric backbones. Self-sorting systems, whereby different molecules or molecular aggregates can assemble themselves with corresponding recognition units, display a critical ability to efficiently distinguish between different recognition units even in a complex mixture or in a system with similar recognition units. For example, Harada et al. found that multiple noncovalent interactions including hydrophobic interactions, p– p stacking and hydrogen-bonding interactions can create a social-self-sorting system cooperatively. Crown ethers, as the first generation of supramolecular macrocyclic hosts, have been widely used as building blocks to construct various functional assemblies with different guest molecules. Based on the differences in binding affinity and binding selectivity between two crown ethers, dibenzo[24]crown-8 (DB24C8) and bis(p-phenylene)[34]crown-10 (BPP34C10), and their complementary guest moieties, dibenzylammonium salts (DBA) and paraquat derivatives, our group has successfully prepared an alternating supramolecular polymer by means of the self-sorting organization of two AB-type heteroditopic monomers. It is of considerable interest to investigate whether it is possible to combine a binary system consisting of a pair of supramolecular polymers through a self-sorting process into a supramolecular polymer blend from low-molecular-weight monomers. For example, if a supramolecular polymer gel is blended with a linear supramolecular polymer, the gelation and other properties of the supramolecular polymer gel can be tuned. Herein we report on a supramolecular polymer blend, which is formed due to the self-sorting organization of two heteroditopic AB-type monomers, 1 and 2 (Scheme 1). Monomer 1 has a DB24C8 moiety and a DBA group, which are linked together by a long and flexible alkyl chain. Monomer 2 contains a BPP34C10-paraquat-based analogue and has [a] S. Dong, X. Yan, B. Zheng, J. Chen, M. Zhang, Prof. Dr. F. Huang Department of Chemistry, Zhejiang University Hangzhou, Zhejiang 310027 (P.R. China) Fax: (+86)571-87953189 E-mail : fhuang@zju.edu.cn [b] X. Ding, Prof. Dr. Y. Yu Shanghai Key Laboratory of Magnetic Resonance Department of Physics, East China Normal University Shanghai 200062 (P.R. China) [c] Dr. D. Xu Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun 130022 (P. R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201200016.

Design and properties of supramolecular polymer gels

Supramolecular polymer gels are precisely designed physical gels brought together by reversible secondary interactions to form three dimensional networks of melt macromolecules. Generally, they differ from supramolecular gels because they are comprised of polymers instead of low molecular weight compounds. Recently, much effort has focused on designing supramolecular polymer gels and related materials with excellent properties; indeed, improvements have been made in their supramolecular interactions, complementarity in the non-covalent bonding units, the nature of the macromolecular building blocks, and strand elasticity of supramolecular polymer networks. Owing to the precise molecular design, they represent nanophase separation and characteristic viscoelasticity. Here, we review supramolecular polymer gels in terms of molecular design, morphology, and rheology. We also discuss future directions in practical application of supramolecular polymer gels.

Four-dimensional structural dynamics of sheared collagen networks

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Preparation and Characterization of Polyfluorene-Based Supramolecular π-Conjugated Polymer Gels

Supramolecular π-conjugated polymer-based gels (SCPGs) are one important kind of semiconducting soft materials. Herein we demonstrate a poly(9,9-dioctylfluorene) (PFO) based on SCPG in 1,2-dichloroethane (DCE). The PFO/DCE gel exhibits a characteristic photoluminescence profile distinguished from other polymorphisms. The emission peak at ca. 550 nm evidences the aggregate or excimer mechanism of the low-energy emission band in polyfluorenes. Thermoreversible sol−gel transition of PFO/DCE gel has been investigated by temperature-resolved fluorescence spectroscopy and differential scanning calorimetry (DSC). The formation mechanism of PFO/DCE gel has been proposed according to the scanning tunneling microscopy (STM) and small-angle X-ray scattering (SAXS) analysis. The obtained xerogel via freeze-drying exhibited regularly interpenetrated pores with the size of about 2−5 μm. Gelation of π-conjugated polymers paves a promising way to prepare porous soft semiconductors with potential applications of sensors a...