Design, Synthesis And Self-Assembly Of Polymers Based On Cucurbituril Structure

Supramolecular chemistry refers to the domain of systems that make up of a discrete number of assembled molecular subunits or components under non-covalent interactions. As an interdisciplinary domain, supramolecular chemistry is undergoing fast development. The research area of supramolecular chemistry crossover several disciplines, including chemistry, physics, biology and material science.Cucurbiturils (CBs) are a series of macrocyclic host molecules that consisted of methylene bridged glycolurils. Based on the number of glycoluril units, CB family consisted of several homologues including CB[5], CB[6], CB[7], CB[8] and CB[10]. CBs demonstrate amazing binding affinity and selectivity to a wide range of guest molecules. The binding constants of CBs to guests cover a broad range of 104-1017 M-1, with a wide range of binding dynamics. These features endow CBs an important role in supramolecular chemistry, which also facilitate their application in the construction of supramolecular assemblies. Moreover, CBs are chemically stable and biological compatible. These properties also support their further applications.In the thesis, on basis of the understanding of CB host-guest interactions, a series of polymers based on CB structures were constructed; their self-assemble properties were characterized and they were further used in the construction of supramolecular polymeric hydrogels.1. In Chapter 2, we designed a molecular switch based on N-methyl-pyrenemethylammonium (MPA+). MPA+demonstrates three binding states with CB[8], that is free MPA+, binary complex MPA+CB[8] and ternary complex MPA+-MV2+CB[8] (here MV2+is dimethylviologen). Under two chemical stimuli of CB[7] and amantadine, MPA+is able to transform among three binding states reversibly and give three fluorescence output. It is worth a note that two stimuli are sufficient to drive the molecular switch even though the switch process of the molecular switch contents four independent processes2. In Chapter 3, N-isopropylacrylamide based CB[7] polypseudorotaxanes were designed. The pseudorotaxane content of the polypseudorotaxanes is low. In the polypseudorotaxanes, the chain segments contain pseudorotaxane units are rigid and the rest chain segments are soft. Such "rigid-soft" alternate structure endows the polypseudorotaxanes unique aggregation behavior, with a strong tendency for aggregation and thermal gelation ability.3. In Chapter 4, CB[7] pendent copolymers were synthesized through free radical copolymerization, and their binding behavior to guests were also characterized. Compare with free CB[7], the binding mode of polymerized CB[7] does not change and the affinity sequence of guests are also similar. Meanwhile, the binding affinities of polymerized CB[7] to guests are 1-2 orders of magnitude lower than free CB[7]. And the binding of a portion of CB[7] to guests are hindered by adjacent CB[7] due to steric hinderance and charge repulse.4. In Chapter 5, we designed supramolecular polymeric hydrogels based on CB[7]-adamantane (CB[7]-AD) crosslinks and proposed the idea to control gelation kinetics with competing guests. Through pre-saturate CB[7] pendent polymer with competing guests, the gelling between CB[7] pendent polymer and AD pendent polymer is impeded. By using various guest molecules and concentrations, the gelation of the hydrogels could be varied from seconds to hours. Based on the controlled gelation of the hydrogels, we also performed proof of concept on their application as injectable and printable hydrogels. The strong interaction of CB[7]-AD pair endow the hydrogels good mechanical properties, stability and shape persistence. Compare to most supramolecular hydrogels, the hydrogels are more similar to covalently cross-linked hydrogels.5. In Chapter 6, we constructed CB[7]-methylviologen (MV) cross-linked supramolecular supramolecular polymeric hydrogels. The CB[7]-MV interaction combines high binding affinity and fast binding dynamics. Such features endow CB[7]-MV cross-linked supramolecular hydrogels premium properties including low critical gelation concentration, good toughness, self-healing ability and stimuli responsiveness.6. In Chapter 7, a click catalyst with tris(triazole)methanol structure was designed. The catalyst demonstrates not only high catalytic activity, but also compatibility to cationic substrates, halogen-ions and free amino groups. Such catalytic features make it perfect for CB guest designation. Based on the catalyst, a CB[8]-based star pseudo[5]rotaxane and a CB[7]-based main-chain alternative polypseudorotaxane were constructed.