Calix[4]arene‐Based Dynamic Covalent Gels: Marriage of Robustness, Responsiveness, and Self‐Healing

Abstract

Herein, the report on a new class of self-healing and pH/temperature responsive mixed solvent (ethanol and water) gels shows unusual mechanical properties to resist slicing, sustain high compression, and withstand stretching as evidenced by the cutting breaking stress, the fracture compressive stress, and the stretching ratio of one of the gels as obtained can reach or exceed 26.4 MPa, 9.2 MPa, and ≈5 times, respectively. The gels are designed by introducing dynamic covalent bond, acylhydrazone, which is believed to combine the merits of conventional chemical bonds and those of supramolecular interactions. Specifically, a hydrazide-modified calix[4]arene derivative and linear benzaldehyde-terminated poly(ethylene glycol)s are synthesized and used as reactive components to build gel networks. Interestingly, acid-degradable hydrogel can be obtained via natural drying of the mixed solvent gel first and then swelling in pure water.

Functional Supramolecular Polymeric Networks: The Marriage of Covalent Polymers and Macrocycle-Based Host–Guest Interactions

“…Calix­[ n ]­arenes can be modified readily on their upper rim, lower rim, or even on the bridging linkages; they have thus been described as being macrocycles with (almost) unlimited possibilities. , Many host–guest recognition systems based on calix­[ n ]­arenes have been investigated, including those based on calix[5]­arenes with primary ammonium salts or C 60 , ,, as well as sulfonatocalix­[ n ]­arenes with MV 2+ , N -alkyl pyridinium salts, trimethyl­ammonium salts, imidazolium salts, or crystal violet. ,− Due to their facile modification, unique structure, and tunable host–guest recognition properties, calix­[ n ]­arenes have been widely used in the field of polymer science, including as catalysts for polymerization, polymer backbones or cores, and as polymer-based grafting units. ,− Calix­[ n ]­arene-based SPNs per se often show desirable stimuli-responsive properties, including changes due to variations in pH, temperature, solvent polarity, and redox environment. This feature has led to their use in a number of applications-related areas, including self-healing, polymer blending, sensing, controlled release, and photo-electricity generation, to name a few. ,− Recent progress involving SPNs produced from covalent polymers and stabilized by calix­[ n ]­arenes-based host–guest interactions (Figure ) is summarized in this section.…”

Morphology-tunable and pH-responsive supramolecular self-assemblies based on AB2-type host–guest-conjugated amphiphilic molecules for controlled drug delivery

“…Alternatively, host–guest-conjugated monomers (HGCMs) which gather host and guest units into one molecule have been studied and attracted many attentions in the field of self-assembly [35]. AB-type HGCMs containing one host and other guest moieties have been used to construct intramolecular complexes [36], cyclic oligomers [37], supramolecular polymers [23,38–40], gels [41–42], etc. However, AB-type HGCMs were still limited to obtain non-spherical stimuli-responsive supramolecular self-assemblies with a tunable morphology transition ability.…”

Stiff-Stilbene-Bridged Biscalix[4]arene as a Highly Light-Responsive Supramolecular Gelator

“…The development of low molecular-mass organic gelators (LMOGs), which self-assemble into fibrous networks that entrap solvent molecules through various noncovalent interactions, has received great attention for potential applications in chemosensing, tissue engineering, drug delivery, − and oil spill recovery. − Incorporating photoswitchable moieties in the molecular design of LMOGs further provides a means to manipulate their morphologies and material properties by light . Recently, our group reported light-responsive supramolecular gelators involving t -butylcalix­[4]­arene and azobenzene structural units, , in which the macrocyclic moieties not only engage in various noncovalent interactions but also provide the cavity space to immobilize solvent molecules for gel formation. − …”