Programmable Polymer‐Based Supramolecular Temperature Sensor with a Memory Function

Abstract

A new class of polymeric thermometers with a memory function is reported that is based on the supramolecular host–guest interactions of poly(N‐isopropylacrylamide) (PNIPAM) with side‐chain naphthalene guest moieties and the tetracationic macrocycle cyclobis(paraquat‐p‐phenylene) (CBPQT4+) as the host. This supramolecular thermometer exhibits a memory function for the thermal history of the solution, which arises from the large hysteresis of the thermoresponsive LCST phase transition (LCST=lower critical solution temperature). This hysteresis is based on the formation of a metastable soluble state that consists of the PNIPAM–CBPQT4+ host–guest complex. When heated above the transition temperature, the polymer collapses, and the host–guest interactions are disrupted, making the polymer more hydrophobic and less soluble in water. Aside from providing fundamental insights into the kinetic control of supramolecular assemblies, the developed thermometer with a memory function might find use in applications spanning the physical and biological sciences.

Giant Single‐Crystal Shape Transformation with Wide Thermal Hysteresis Actuated by Synergistic Motions of Molecular Cations and Anions

“…Therefore, such a large and robust thermal hysteresis is unusual in mechanical responsive materials (see Table S2). The two distinct physical states (elongation and shortening) along with a remarkable wide and stable hysteresis window demonstrated in the present compound provide a potential basis for memory devices …”

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

“…We designed a supramolecular hydrogel system featuring a non‐thermoresponsive poly( N , N ‐dimethylacrylamide) hydrogel functionalized with dialkoxynaphthalene guest units (NaphtGel; Figure a) that significantly swells upon complexation with the tetracationic cyclophane host cyclobis(paraquat‐ p ‐phenylene) (CBPQT 4+ ). On the basis of our previous observation that the supramolecular association of CBPQT 4+ and PNIPAM polymers containing electron‐rich guest units can be thermally controlled, we envisioned that the combination of NaphtGel with CBPQT 4+ and a PNIPAM end‐functionalized with tetrathiafulvalene (TTF‐PNIPAM) as a competitive guest would lead to temperature‐induced swelling of NaphtGel (Figure b). In this three‐component system, TTF‐PNIPAM will be complexed with CBPQT 4+ below the LCST phase transition, as TTF is a more strongly binding guest than naphthalene.…”

Adamantane Functionalized Poly(2-oxazoline)s with Broadly Tunable LCST-Behavior by Molecular Recognition

“…For this purpose, several hydrophilic hosts have been utilized to accommodate a variety of pendant hydrophobic groups on the polymer chains. Most notable is the utilization of various macrocycles, such as cucurbit[7]urils [ 40 ], pillararenes [ 41 , 42 ], and cyclobis(paraquat- p -phenylene)s [ 43 , 44 ] to modulate the LCST behavior of thermoresponsive polymers through complexation with polymer termini or side chains [ 40 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. Among these different hosts, cyclodextrins have been prominently featured for the modulation of thermoresponsive behavior, as they can accommodate a wide variety of hydrophobic guest molecules, have an extensively studied complexation chemistry, and various sizes (α, β, and γ-cyclodextrin) [ 52 ] and chemical variants are commercially available or can be readily prepared [ 53 , 54 ].…”