The Construction Of Functional Supramolecular Polymeric Materials Via The Combination Of Traditional Polymers And Crown Ether/Pillararene-Based Recognition Motifs

Supramolecular polymeric materials, which emerged as the marriage of supramolecular chemistry and polymer science, have gained considerable interest in recent years as excellent materials not only due to their properties similar to traditional polymers which are built by covalent bonds, but also because of the reversibility and stimuli-responsiveness of the noncovalent bonds. Macrocylic hosts, including crown ethers, cyclodextrins, calixarenes, cucurbiturils, and pillararenes, are the most commonly used building blocks in the fabrication of host-guest interaction-based supramolecular polymeric materials. Among them, the association between crown ethers, the first generation of artificial supramolecular hosts, and guest molecules has been utilized to construct various supramolecular polymeric materials. Moreover, pillararenes, a kind of novel supramolecular hosts, have been utilized to fabricate different kinds of supramolecular assemblies, their application in the field of supramolecular polymeric materials has been still rarely explored. In this thesis, we reported the construction of functional supramolecular polymeric materials via the combination of traditional polymers and crown ether/pillararene-based recognition motifs. The main content of the dissertation includes the following seven parts:In the first part, a novel supramolecular amphiphilic polymer constructed by crown ether-based molecular recognition has been fabricated and demonstrated to self-assemble into core-shell supramolecular micelles in water. The reversible transition between assembled and disassembled structures can be achieved by changing the pH. This transition was used to realize the controlled release of small molecules. The release of hydrophobic molecules from the micelles was realized by adding acid (aqueous HCl), weakening the host-guest interactions and leading to disassembly of the supramolecular micelles.In the second part, a supramolecular cross-linked network was fabricated and demonstrated to act as a multiple fluorescent sensor. It was constructed from a fluorescent conjugated polymer and a bisammonium salt cross-linker driven by dibenzo[24]crown-8/secondary ammonium salt host-guest interactions. Compared with the conjugated polymer, the network has weak fluorescence due to the aggregation of polymer chains. Thanks to the multiple stimuli-responsiveness of host-guest interactions, the fluorescence intensity of the system can be enhanced by four types of signals, including potassium cation, chloride anion, pH increase, and heating. Hence, the network can serve as a cation sensor, an anion sensor, a pH sensor, and a temperature sensor. It can be used in both solution and thin film. Interestingly, exposure of a film made from this supramolecular cross-linked network to ammonia leads to an increase of fluorescence, making it a good candidate for gas detection.In the third part, a novel diblock copolymer with a hydrophobic supramolecular polymer block and a hydrophilic traditional polymer block was prepared. Control over the chain length ratio of the two blocks was obtained by simply changing the concentration proportion of the monomer of the supramolecular polymer block to the traditional polymer block in solution. Intricate organic or polymer synthesis was unnecessary. Furthermore, when the chain length ratio of the two blocks was changed, the formation of various self-assembly morphologies was achieved. Micelles with the controlled release function of hydrophobic molecules were formed when the chain length of the hydrophilic traditional polymer block was longer than that of the hydrophobic supramolecular polymer block, while vesicles with the controlled release function of hydrophilic molecules were obtained under the opposite condition.In the fourth part, polymer blends play a significant role in polymer science due to their new and unique properties compared to the individual polymer components. However, most of the polymer blends are immiscible and not adaptive to the environment stimuli, impacting their application in modern polymer industry. Herein, we made an enhancement of the compatibility of an immiscible poly(methy acrylate)/polystyrene blend based on multiple-responsive benzo-21-crown-7/dialkylammonium salt host-guest interactions. Owing to the multi-responsiveness and reversibility of benzo-21-crown-7/dialkylammonium salt host-guest interactions, the polymer blend could recover its compatibility after damaged by environmental factors, indicating the adaptiveness of this polymer blend.In the fifth part, supramolecular crosslinked polymer gels show fascinating properties contributed by both mechanical properties of covalently jointed polymer chains and the reversibility and stimuli-responsiveness of supramolecular interactions, making them ideal candidates for environment-adaptive materials. Usually the previously reported supramolecular crosslinked polymer gels contain only one kind of physical cross-link. Here we report a novel supramolecular polymer gel contains two types of physical crosslinks based on two kinds of non-covalent interactions, DAN-DeUG quadruply hydrogen-bonding interactions and B21C7/dialkylammonium salt host-guest interactions, respectively. One of them is used to keep the gel state, and the other one is employed for changing the crosslinking density of the gel under external stimuli, thereby causing the volume change of the gel. This double supramolecular crosslinked polymer gel shows macroscale expansion and contraction behavior and multistimuli responsiveness. Therefore, we successfully demonstrate that the macroscopic property change of supramolecular systems can be induced by the control of self-assembly on the molecular scale.In the sixth part, based on the combination of B21C7/dialkylammonium salt host-guest interactions and tetraphenylethylene (TPE)-based aggregation-induced emission (AIE) effect, a fluorescent supramolecular crosslinked polymer gel was successfully prepared. Compared with the solution of TPE-containing small molecules, this gel exhibited remarkable fluorescence enhancement due to the AIE effect of TPE units. The "gelation induced fluorescence emission" phenomenon can be explained by the hindered intramolecular rotation of phenyl rings of TPE. Because of the reversibility and stimuli-responsiveness of the B21C7/dialkylammonium salt host-guest interactions, the transition between the fluorescent supramolecular crosslinked polymer gel and the disassembled sol with very weak fluorescence can be realized by adding pH and thermal stimuli. This novel material contributes to the development of supramolecular chemistry, polymer science and fluorescent materials and offers a new method to construct functional supramolecular materialsIn the last part, we demonstrate the precise control on the LCST behavior of a thermoresponsive polymer in water by pillararene-based host-guest interactions. The LCST value of the polymer increases upon the stepwise addition of either of the two pillararene hosts. On account of the pH-responsiveness of the pillararene-based host-guest interactions, the recovery of the LCST is achieved with the treatment of acid, reflecting the pH-responsive supramolecular control on the LCST.