Study On The Synthesis And Properties Of Host Macrocyclic Molecule Based Supramolecular Gels

The main part of supramolecular chemistry is molecular recognition and molecular assembly via non covalent interaction such as electrostatic interaction, Van der Waals’ force, hydrophobic bond, hydrogen bond,π-π interaction and charge-transfer interaction. The host molecule (receptor) packaging with guest molecule (substrate) leads to new physical and chemical properties via supramolecular interactions. Cyclodextrins (CDs) are frustum shaped macrocycle molecules which have been extensive basic studied over years and decades. It has hydrophobic cavity and hydrophilic ectotheca thus leading to self-assembly between CD and guests. Because of its hypotoxicity and degradability, CD can be used as food additives and cosmetic ingredients. Cucurbit[n]uril (CB[n]) is cyclic methylene-bridged glycoluril oligomer which has an opened hydrophobic cavum. The cavities of CB[6,7,8] are similarly sized to α-,β -and y-CD. CB[n] has carbonyls on its two poles which can selectively bond metal ions and positive center of organic guests via ion-dipole interaction. In CB[n] family, CB[8] has a suitable cavum to selectively form trimolecular complex with an electron donor (such as naphthyl, Np) and an electron acceptor (such as methylviologen, MV2+) via CB[8]-enhanced charge-transfer (CT) interaction. Therfore, CB[8] can be used to prepare supramolecular gels. In addition, because of high rigidity and large size of macrocycle molecules, the CD- and CB[n]-based side-chain polypseudorotaxanes had different properties to the unassembled polymers. The main work of this paper is as follows:1. A temperature-sensitive copolymer with Np on its side-chain (PVBN-co-NIPAA) was synthesized by copolymerization of 2-((4-vinylbenzyl)oxy)naphthalene (VBN) with N-isopropylacrylamide (NIPAA). Host-guest complexes PVN-R with different packing ratio can be prepared by mixing PVBN-co-NIPAA with different content of MV2+ and CB[8] in aqueous solution. These NIPAA-based host-guest complexes had the lower critical solution temperature (LCST) in water solvent and measured by ultraviolet and visible spectrophotometry (uv-vis). Below LCST, PVN-R solved in water and formed rad solution. However, when heated above LCST, the solutions turned into non-transparent supramolecular hydrogels. The results of rheological measurement and uv-vis showed that the change of copolymerization ratio of PVBN-co-NIPAA and threaded ratio of CB[8] both lead to various thermo-gelling behavior. High threaded ratio lead to high gelation temperature, and increased copolymerization ratio of VBN unit lower it. In addition, these supramolecular hydrogels had stabilized rheological property even at low polymer content (0.75 wt%).2. A NIPAA-based temperature-sensitive copolymer with amantadine (Ad) on it side-chain (VBAd-co-NIPAA) was synthesized by the copolymerization of N,N-dimethyl-N-(4-vinylbenzyl)-N- adamantine ammonium chloride (VBAd) with N-isopropylacrylamide (NIPAA). The structure, compositions and molecular weight of the copolymer were characterized by 1H NMR spectrum and static laser light scattering. Side chain polypseudorotaxanes VANIPAA-CD and VANIPAA-CB were prepared by mixing VBAd-co-NIPAA with β-CD and CB[8] in aqueous solution, respectively. Cloudy points of polypseudorotaxanes with different packing ratio in water were tested by turbidimeter and indicated that they had the same cloudy point at 34 ℃. Above 34 ℃, VANIPAA-CB precipitated from water and VANIPAA-CD formed opaque hydrogel. Thermo-gelling process of VANIPAA-CD was measured by torque rheometer indicating that increasing packing ratio of P-CD on polypseudorotaxanes lead to low gelation temperature. The microstructure of these supramolecular hydrogels was measured by transmission electron microscope (TEM).3. A side-chain MV2+ hydrosoluble copolymer VBMV-co-DMA was prepared by the copolymerization of N-methyl-N-(4-vinylbenzyl)-4,4-bipyridine (VBMV) with N,N-dimethylacrylamide and its copolymerization ratio was calculated by 1H nuclear magnetic resonance (1H NMR).2-((6-Bromohexyl)oxy)naphthalene was synthesised and reacted with SiO2-NH2 to introduce Np on the surface of SiO2 nanoparticles (SiO2-Np). Copolymer VBMV-co-DMA and SiO2-Np mixing with CB[8] in DMSO/H2O solvent can form opaque supramolecular gel via CT interaction. Result of rheological measurement showed that supramolecular gel with high ratio of DMSO/H2O preformed preferably.