Recognition‐Mediated Hydrogel Swelling Controlled by Interaction with a Negative Thermoresponsive LCST Polymer

Abstract

Most polymeric thermoresponsive hydrogels contract upon heating beyond the lower critical solution temperature (LCST) of the polymers used. Herein, we report as upramolecular hydrogel system that shows the opposite temperature dependence.W hen the non-thermosesponsive hydrogel NaphtGel, containing dialkoxynaphthalene guest molecules,b ecomes complexed with the tetra cationic macrocyclic host CBPQT 4+

Supramolecular Competitive Host–Guest Interaction Induced Reversible Macromolecular Metamorphosis

“…The absorbance due to the Naph‐CBPQT 4+ complex was not visible in the UV–vis spectrum as it is eclipsed by the more intense absorbance of oxidized TTF . Again, with the addition of aqueous ascorbic acid solution which reduces the oxidized TTF, the peak around 800 nm reappeared indicating the restoration of the linear supramolecular architecture . Similar complexation and decomplexation of TTF, Naph, and CBPQT 4+ were also reported by Stoddart et al in case of their molecular‐mechanical switching of bistable[2]rotaxane structures coated on metal nanoparticles.…”

“…Whereas, Naph‐PHEA carrying a Naph unit at the chain end was prepared by RAFT polymerization of HEA using a Naph‐CTA (detailed polymerization in the Supporting Information) . TTF‐PNIPAM was synthesized according to a previously reported procedure (detailed polymerization in the Supporting Information) . The formation of the obtained structures were confirmed by their corresponding 1 H NMR spectra (Figures S4, S5, S7, S9, and S11, Supporting Information).…”

“…The macromolecular architecture reversibly changes based on the simple competitive host–guest supramolecular interaction of 1,5‐dialkoxynaphthalene (Naph) end‐ and side‐chain functionalized polyacrylate and tetrathiafulvalene (TTF) end‐functionalized poly(N‐isopropylacrylamide) (PNIPAM) as guests and tetracationic cyclophane host cyclobis(paraquat‐ p ‐phenylene) (CBPQT 4+ , 4PF 6 − ) functionalized poly(2‐ethyl‐2‐oxazolines) (PEtOx). The stronger binding affinity of TTF, due to its higher π‐electron density towards CBPQT 4+ compared to that of Naph, and the easy modularity of TTF electron density by reversible oxidation and reduction made it possible to control the complexation between CBPQT 4+ , TTF, and Naph unit by reversible redox switching . In particular, as the oxidized TTF did not form any complex with CBPQT 4+ due to its lack of electron density, this redox switching complexation was exploited in this work to induce supramolecular metamorphosis in the polymer architecture …”

“…The coulombic repulsion arises between the oxidized TTF and CBPQT 4+ ring caused this rapid decomplexation of TTF‐CBPQT 4+ complex. As a consequence of this decomplexation, the free PEtOx‐CBPQT 4+ formed the complex with P(HEA‐co‐NaphDEGA) reverting the supramolecular polymer topology back to the comb architecture . The absorbance due to the Naph‐CBPQT 4+ complex was not visible in the UV–vis spectrum as it is eclipsed by the more intense absorbance of oxidized TTF .…”

Triple responsive block copolymers combining pH‐responsive, thermoresponsive, and glucose‐responsive behaviors

“…A number of polymeric systems have been shown to exhibit reversible changes in conformation or solubility in response to environmental changes, making these materials attractive for use in areas like drug delivery, analyte sensing, or tissue engineering . By selectively incorporating certain functional groups, such responsive materials can undergo a number of property changes as a result of external influences, including non‐chemical stimuli such as light or temperature, or through chemical stimuli such as changes in pH, redox reactions, or dynamic‐covalent, and supramolecular interactions . Photoresponsive materials often demonstrate reversible isomerization upon irradiation and commonly include materials with azobenzene moieties or spiropyrans .…”