Self-assembly And Applications Of Amphiphilic Linear-hyperbranched Supramolecular Polymers

Supramolecular chemistry has been developed flourishingly since theNobel Prize was given to C. J. Pedersen, J. M. Lehn and D. J. Cram fortheir contributions to supramolecular chemistry in1987. For the efforts ofscientists in various fields, the concept of supramolecular chemistry hasexpanded to the field of organic chemistry, inorganic chemistry, materialscience, medical science, life science and so on, and with many remarkableachievements appeared. As a reflection of supramolecular chemistry inpolymer science, supramolecular polymers have become the focus becauseof its unique physicochemical properties, easy-prepared feature andoutstanding processability. Supramolecular polymer is defined aspolymeric arrays of monomer units held together by non-covalent bonds.Recently, those macromolecules in which macromolecules served as atleast one component linked together via non-covalent bonds, are alsoclassified as supramolecular polymers. In this dissertation, based uponprevious researches on the preparation and self-assembly ofsupramolecular polymers, we synthesized two kinds oflinear-hyperbranched supramolecular polymers using host/guestinteractions, and investigated their self-assembly behavior in water. Inaddition, as an application of such linear-hyperbranched supramolecularpolymer, we investigated the reversible transition between hydrophobicand hydrophilic of the polymer-modified Au surface. The main researchcontents and results are as follows:1. Synthesis and its photoresponsive self-assembly behavior oflinear-hyperbranched supramolecular block copolymer polystyrene-b-polyglycerol (PS-b-HPG):Hydrophilic hyperbranched polyglycerol with β-cyclodextrin as focalpoint (CD-g-HPG) and hydrophobic linear polystyrene with azobenzene asfocal point (AZO-g-PS) were prepared via oxyanionic ring-openingmultibranching polymerization and reversible addition-fragmentationchain transfer polymerization, respectively. By adding water to the DMFsolution of CD-g-HPG and AZO-g-PS, amphiphilic supramolecularpolymer PS-b-HPG was obtained through the recognition of CD and AZOmoieties. Self-assembled aggregates were obtained after removing DMFby dialysis against pure water. The formation of supramolecular polymerPS-b-HPG was monitored by DLS and proved by2D NOESY spectrum.Sphere micelles were observed by SEM and TEM prepared from thePS-b-HPG aqueous solution. When exposed to UV irradiation, azobenzenegroups would undergo isomerization. As a result, the host/guest interactionwould be destroyed, and the self-assemblies disassembled. This kind ofphotoresponsive micelles may find applications as microreactors anddelivery vehicles, endowing much significance to the research.2. The transition between hydrophobic and hydrophilic of Au surfacemodified by a photoresponsive linear-hyperbranched supramolecularpolymer PMMA-b-HPG.Hydrophilic hyperbranched polyglycerol with β-cyclodextrin as focalpoint (CD-g-HPG) and hydrophobic linear poly(methyl methacrylate) withazobenzene as focal point (AZO-g-PMMA) were prepared via oxyanionicring-opening multibranching polymerization and reversibleaddition-fragmentation chain transfer polymerization, respectively. Anamphiphilic supramolecular copolymer PMMA-b-HPG was obtained bythe mixture of CD-g-HPG and AZO-g-PMMA through the host/guestinteraction of CD and AZO groups. Then the supramolecular polymer canadhere to Au surface because of the S-Au bond formed by Au andtrithiocarbonate, which is introduced to the AZO-g-PMMA part by thechain transfer agent used in RAFT polymerization. As the host/guest interaction between CD and AZO can be destroyed under UV irradiation,CD-g-HPG will be departed from PMMA-b-HPG-modified Au surface andthe surface undergoes a transition from hydrophilic to hydrophobic as aresult. Under visible light irradiation, however, the hydrophilic propertycan be recovered by immersing Au surface into a CD-g-HPG solution. Inthis way, the modified Au surface can accomplish a reversible transitionbetween hydrophilic and hydrophobic. The interaction betweentrithiocarbonate and Au was proved by XPS. The formation ofsupramolecular polymer PMMA-b-HPG was proved by2D NOESYspectrum. The reversible transition between hydrophilic and hydrophobicof Au surface was proved by water contact angle (CA). This kind ofphotoresponsive supramolecuar polymer may find applications in areassuch as surface modification, biosensors and electrochemical applications.