DOSY NMR as a tool for predicting optimal conditions for hydrogel formation: The case of a hyperbranched polyglycidol cross-linked with boronic acids

Synergistic Covalent-and-Supramolecular Polymers with an Interwoven Topology

Network topologies, especially some high-order topologies, are able to furnish cross-linked polymer materials with enhanced properties without altering their chemical composition. However, the fabrication of such topologically intriguing architectures at the macromolecular level and in-depth insights into their structure-property relationship remain a significant challenge. Herein, we relied on synergistic covalent-and-supramolecular polymers (CSPs) as a platform to prepare a range of polymer networks with an interwoven topology. Specifically, through the sequential supramolecular self-assemblies, the covalent polymers (CPs) and metallosupramolecular polymers (MSPs) could be interwoven in our CSPs by [2]pseudorotaxane cross-links. As a result, the obtained CSPs possessed a topological network that could not only promote the synergistic effect between CPs and MSPs to afford mechanically robust yet dynamic materials but also vest polymers with some functions, as manifested by force-induced hierarchical dissociations of supramolecular interactions and superior thermomechanical stability compared to our previously reported CSP systems. Furthermore, our CSPs exhibited tunable mechanical performance toward multiple stimuli including K⁺ and PPh₃, demonstrating abundant stimuli-responsive properties. We hope that these findings could provide novel opportunities toward achieving topological structures at the macromolecular level and also motivate further explorations of polymeric materials via the way of controlling their topological structures.

Self-Healable, Injectable Hydrogel with Enhanced Clotrimazole Solubilization as a Potential Therapeutic Platform for Gynecology

Injectable, self-healing hydrogels with enhanced solubilization of hydrophobic drugs are urgently needed for antimicrobial intravaginal therapies. Here, we report the first hydrogel systems constructed of dynamic boronic esters cross-linking unimolecular micelles, which are a reservoir of antifungal hydrophobic drug molecules. The selective hydrophobization of hyperbranched polyglycidol with phenyl units in the core via ester or urethane bonds enabled the solubilization of clotrimazole, a water-insoluble drug of broad antifungal properties. The encapsulation efficiency of clotrimazole increases with the degree of the HbPGL core modification; however, the encapsulation is more favorable in the case of urethane derivatives. In addition, the rate of clotrimazole release was lower from HbPGL hydrophobized via urethane bonds than with ester linkages. In this work, we also revealed that the hydrophobization degree of HbPGL significantly influences the rheological properties of its hydrogels with poly(acrylamide-ran-2-acrylamidephenylboronic acid). The elastic strength of networks (G_N) and the thermal stability of hydrogels increased along with the degree of HbPGL core hydrophobization. The degradation of the hydrogel constructed of the neat HbPGL was observed at approx. 40 °C, whereas the hydrogels constructed on HbPGL, where the monohydroxyl units were modified above 30 mol %, were stable above 50 °C. Moreover, the flow and self-healing ability of hydrogels were gradually decreased due to the reduced dynamics of macromolecules in the network as an effect of increased hydrophobicity. The changes in the rheological properties of hydrogels resulted from the engagement of phenyl units into the intermolecular hydrophobic interactions, which besides boronic esters constituted additional cross-links. This study demonstrates that the HbPGL core hydrophobized with phenyl units at 30 mol % degrees via urethane linkages is optimal in respect of the drug encapsulation efficiency and rheological properties including both self-healable and injectable behavior. This work is important because of a proper selection of a building component for the construction of a therapeutic hydrogel platform dedicated to the intravaginal delivery of hydrophobic drugs.

Mechanically interlocked networks cross-linked by a molecular necklace

Molecular necklaces have attracted much research attention due to their unique topological structures. Although numerous molecular necklaces with exquisite structures have been constructed, it remains a major challenge to exploit the functions and applications associated with their fascinating architectural and dynamic characteristics. Herein, we report a class of mechanically interlocked networks (MINs) cross-linked by a molecular necklace, in which multiple crown ethers are threaded on a hexagonal metallacyclic framework to furnish a cross-linker with delicate interlocked structures. The molecular necklace cross-linker possesses multiple peculiar advantages: multivalent interactions and rigid metallacycle framework guarantee robust features of MINs while the motion and dissociation of the interlocked structures bring in notable mechanical adaptivity. Moreover, the MINs could respond to the stimuli of K⁺ and Br⁻, which lead to the dethreading of crown ether and even the complete decomposition of molecular necklace, respectively, showing abundant active properties. These findings demonstrate the untapped potential of molecular necklaces as cross-linkers and open the door to extend their advanced applications in intelligent supramolecular materials.

Constructing cross-linked networks with different topologies is attractive but challenging. Here the authors present mechanically interlocked networks cross-linked by a molecular necklace whose peculiar architectural and dynamic features endow the materials with robust yet mechanically adaptive properties.

Molecular Characterization of Polymer Networks

Polymer networks are complex systems consisting of molecular components. Whereas the properties of the individual components are typically well understood by most chemists, translating that chemical insight into polymer networks themselves is limited by the statistical and poorly defined nature of network structures. As a result, it is challenging, if not currently impossible, to extrapolate from the molecular behavior of components to the full range of performance and properties of the entire polymer network. Polymer networks therefore present an unrealized, important, and interdisciplinary opportunity to exert molecular-level, chemical control on material macroscopic properties. A barrier to sophisticated molecular approaches to polymer networks is that the techniques for characterizing the molecular structure of networks are often unfamiliar to many scientists. Here, we present a critical overview of the current characterization techniques available to understand the relation between the molecular properties and the resulting performance and behavior of polymer networks, in the absence of added fillers. We highlight the methods available to characterize the chemistry and molecular-level properties of individual polymer strands and junctions, the gelation process by which strands form networks, the structure of the resulting network, and the dynamics and mechanics of the final material. The purpose is not to serve as a detailed manual for conducting these measurements but rather to unify the underlying principles, point out remaining challenges, and provide a concise overview by which chemists can plan characterization strategies that suit their research objectives. Because polymer networks cannot often be sufficiently characterized with a single method, strategic combinations of multiple techniques are typically required for their molecular characterization.

Hyperbranched polymer hydrogels with large stimuli-responsive changes in storage moduli and peroxide-induced healing

Hydrogels prepared using hyperbranched polymers with dynamic disulfide bonds show larger changes in moduli upon exposure to chemical stimuli for both softening and stiffening responses compared to linear polymers.

Chemoresponsive polymer systems for selective molecular recognition of organic molecules in biological systems

Smart polymer materials that respond to a chemical stimulus are applied for the construction of biomedical devices and purification/separation systems. Small organic molecules are a particular type of stimulus. Their abnormal concentration indisputably indicates certain diseases. They are also hazardous environment contaminants. Polymer materials, which structure is selectively changed in the presence of a defined organic compound are promising in view of regulation of certain biomedical functions, as well as in view of chemical detectors construction. This review summarizes the state of the art in the self-assemblies of amphiphilic copolymers and polymer networks sensitive toward organic species, with an emphasis on the reports from the last decade. We focus on the relationship between the selectivity of introduced receptor moieties responsible for the change of material structure, the overall structure of material and its functionality.