Jianzhuang Chen

A Multiresponsive, Shape‐Persistent, and Elastic Supramolecular Polymer Network Gel Constructed by Orthogonal Self‐Assembly

A cross-linked supramolecular polymer network gel is designed and prepared, which shows reversible gel-sol transitions induced by changes in pH, temperature, cation concentration, and metal co-ordination. The gel pore size is controlled by the amount of cross-linker added to the system, and the material can be molded into shape-persistent, free-standing objects with elastic behavior. These features are all due to the dynamically reversible host-guest complexation and good mechanical properties of the cross-linked polymer network. No single organogel has previously been reported to possess all of these features, making this supramolecular gel an unprecedentedly intelligent soft material.

Self‐Healing Supramolecular Gels Formed by Crown Ether Based Host–Guest Interactions

Automatic repair: a polymer with pendent dibenzo[24]crown-8 units (purple in picture) was cross-linked by two bisammonium salts (green) to form two supramolecular gels based on host-guest interactions. These two gels are stimuli-responsive materials that respond to changes of the pH value and are also self-healing materials, as can be seen by eye and as evidenced by rheological data.

Pillar[6]arene-Based Photoresponsive Host–Guest Complexation

The trans form of an azobenzene-containing guest can complex with a pillar[6]arene, while it cannot complex with pillar[5]arenes due to the different cavity sizes of the pillar[6]arene and the pillar[5]arenes. The spontaneous aggregation of its host-guest complex with the pillar[6]arene can be reversibly photocontrolled by irradiation with UV and visible light, leading to a switch between irregular aggregates and vesicle-like aggregates. This new pillar[6]arene-based photoresponsive host-guest recognition motif can work in organic solvents and is a good supplement to the existing widely used cyclodextrin/azobenzene recognition motif.

Supramolecular polymers with tunable topologies via hierarchical coordination-driven self-assembly and hydrogen bonding interfaces

A powerful strategy to obtain complex supramolecular materials is the bottom-up construction of noncovalently bound materials by hierarchical self-assembly. This assembly process involves stepwise, uniform increases to the architectural complexity of a substrate, starting from discrete precursors and growing in dimensionality through controlled reactivity to a final product. Herein, two orthogonal processes are exploited: coordination-driven self-assembly and hydrogen bonding. The former relies on the predictable formation of metal–ligand bonds wherein the directionalities of the rigid precursors used determines the structural outcome. The latter uses 2-ureido-4-pyrimidinone interfaces that are structurally robust by virtue of the quadruple hydrogen bonding that can occur between subunits. By combining these two processes into a single system, it is possible to generate hierarchical materials that preserve the attractive tunability associated with discrete supramolecular coordination complexes. For instance, the synthesis of a one-dimensional chain comprising linked metalla-rhomboids is readily adapted to a 2D cross-linked hexagonal network by simply selecting a different metal acceptor precursor as an assembly component. The specific interactions between subunits, in this case platinum(II)-pyridyl bonds and the quadruple H-bonding of ureidopyrimidinone, are unchanged, establishing a unique strategy to obtain supramolecular polymers with marked topological differences with minimal synthetic redesign. In addition, the structural rigidity imposed by the inclusion of the platinum metallacycles serves to minimize the formation of cyclic oligomers, increasing the efficacy of formation and improving the properties of the resultant materials. Furthermore, this study taps the potential of organoplatinum(II) metallacycles in materials science.

Supramolecular polymer nanofibers via electrospinning of a heteroditopic monomer.

Driven by the benzo-21-crown-7/secondary ammonium salt recognition motif, a linear supramolecular polymer was formed from self-organization of a low-molecular-weight self-complementary monomer in chloroform. From this supramolecular polymer, nanofibers were obtained successfully via electrospinning.

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 Dual-Thermoresponsive Gemini-Type Supra-amphiphilic Macromolecular [3]Pseudorotaxane Based on Pillar[10]arene/Paraquat Cooperative Complexation

Herein, first we report the preparation of a thermoresponsive [3]pseudorotaxane from cooperative complexation between a water-soluble pillar[10]arene and a paraquat derivative in water. Then we successfully construct the first pillararene-based gemini-type supra-amphiphilic [3]pseudorotaxane from the water-soluble pillar[10]arene and a paraquat-containing poly(N-isopropylacrylamide) based on this new molecular recognition motif in water. This macromolecular [3]pseudorotaxane shows unique dual-thermoresponsiveness. Furthermore, it can self-assemble into polymeric vesicles at 37 °C in water. These vesicles can be further used in the controlled release of small molecules induced by cooling to 25 °C or heating to 60 °C.

Adjustable supramolecular polymer microstructures fabricated by the breath figure method

Highly ordered supramolecular polymer honeycomb-patterned films were fabricated successfully via the static breath figure method. The supramolecular polymer that was used to prepare these intriguing films was obtained from the self-organization of a heteroditopic monomer based on the benzo-21-crown-7/secondary ammonium salt recognition motif. The morphologies of these microstructures were observed by scanning electron microscopy, optical microscopy and atomic force microscopy techniques. The monomer concentration plays an important role in the fabrication of these supramolecular polymer microstructures. The pore size of honeycomb-patterned films decreases with the increase of the monomer concentration from 4 wt% to 30 wt%. A microsphere (900 nm) pattern and a highly-ordered honeycomb-patterned film (2.0 μm) were obtained via the static breath figure method using acetonitrile as the solvent at concentrations of 2 wt% and 30 wt%, respectively.

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.

Dual-responsive crown ether-based supramolecular chain extended polymers

Based on the benzo-21-crown-7 (B21C7)/secondary ammonium salt molecular recognition motif, dual-responsive supramolecular chain extended polymers with a biodegradable poly(e-caprolactone) (PCL) chain as the scaffold were successfully prepared by self-assembly of a heteroditopic macromonomer which was synthesized by a combination of ring-opening polymerization and click reaction. 1H NMR spectroscopy, FT-IR, solution viscometry, diffusion NMR and differential scanning calorimetry were employed to characterize these novel supramolecular chain extended polymers. Due to the environmental responsiveness of the recognition of the B21C7 host unit to the secondary ammonium salt guest moiety, the supramolecular chain extended polymers respond to pH and cation stimuli. The crystallization behavior of the PCL segments of the supramolecular chain extended polymers and the neutral counterpart were investigated by polarized optical microscopy. The B21C7/secondary ammonium salt host–guest interactions cause a decrease of the chain mobility of PCL and make the crystallization rate of PCL much slower in comparison with the case of the neutral counterpart.