Self-assembly Of Light-responsive Hyperbranched Polymer Vesicles

Branched polymersomes（BPs）are novel polymer vesicles self-assembled from amphiphilic hyperbranched polymers.BPs have displayed special properties including controllable size,robust stability,good fluidity and facile surface functionalization,so they have attracted increasing attention after the first invention in 2004.Up to now,BPs have shown great potentials in many areas including nanocontainers,cytomimetic chemistry and biomedical applications.This thesis contains three parts and has reported several light-responsive hyperbranched polymersomes through the combination of BPs with different light-responsive groups or quantum dots.The main contents and results are shown as follows:1.Synthesis of a linear-hyperbranched supramolecular polymer and its light-responsive self-assembly behaviorA hyperbranched polyglycerol with aβ-cyclodextrin（β-CD）group in the center,CD-g-HPG,was synthesized through anionic ring-opening multibranching polymerization（ROMBP）of glycerol by usingβ-CD as a multi-hydroxyl initiator together with a slow monomer addition technique.A linear polymer AZO-PS with an azobenzene group at the end of polystyrene was synthesized via atom transfer radical polymerization（ATRP）method.The linear AZO-PS and hyperbranched CD-g-HPG were conjugated together through the specific CD/AZO host-guest interaction,leading to the formation of a“linear-hyperbranched”supramolecular polymer PS-b-HPG.This supramolecular polymer was amphiphilic and could self-assemble into vesicles in water.The host-guest complexation ability between AZO-PS and CD-g-HPG was characterized by UV-Vis titration.The self-assemblies of PS-b-HPGs were characterized by SEM and TEM.At last,we showed that the vesicles from PS-b-HPGs could disassemble under UV light due to the trans-to-cis isomerisation of the AZO groups.2.The praparation and characterization of Janus hybrid fluorescent vesiclesAmphiphilic hyperbranched copolymer HBPO-star-PEO was synthesized by the cationic ring-opening polymerization.β-CD and adamantane（Ada）modified amphiphilic hyperbranched copolymers（HBPO-star-PEO-CD and HBPO-star-PEO-Ada）were synthesized by the modifications of terminal-groups of HBPO-star-PEOs.The QBPs（QBP-1、QBP-2 and QBP-3）were prepared by co-self-assembly of HBPO-star-PEO,HBPO-star-PEO-CD or HBPO-star-PEO-Ada,and the quantum dots（QDs）（CdSe/CdS,（Zn）CuInS/ZnS or Fe₃O₄）through the film rehydration method.Here,QBP-1 means CD-modified BPs incorporated with CdSe/CdS QDs,QBP-2 means Ada-modified BPs incorporated with（Zn）CuInS/ZnS QDs,and QBP-3 means Ada-modified BPs incorporated with Fe₃O₄ QDs.Under the irradiation of fluorescence,QBPs could emit different fluorescence due to the encapsulated QDs.QBP-1 together with QBP-2 or QBP-3 could fuse with each other after coalescence through the intervesicular CD-Ada host–guest recognition,and generated Janus fluorescent QBPs（JQBP-1 and JQBP-2）at last.JQBP with a half sphere in red and the other half in green or a half sphere in red and the other half in blue were clearly observed under the fluorescence microscope.The giant dimension of BPs allowed the real-time observation of the membrane fusion process under fluorescence microscope,which revealed the formation mechanism of the JQBPs.Moreover,a potential magnetically-controlled display application of the Janus vesicles with a Fe₃O₄-containing hemisphere was demonstrated.3.Construction of light-harvesting systems based on BPsCD-functionalized BPs（CD-BPs）were prepared through the coassembly of HBPO-star-PEOs and HBPO-star-PEO-CD in aqueous solution.The vesicular light harvesting system with spatially separated donors and acceptors was constructed by incorporating the hydrophobic donors into the hydrophobic core layers of the vesicles and by fixing the hydrophilic acceptors on the vesicle surfaces.The light-harvesting process was characterized by optical microscopy（OM）,fluorescent microscopy（FM）,and photoluminescence（PL）spectrum.The vesicular light harvesting system can effectively avoid theπ-πstacking between the donors and can provide a suitable distance between donors and acceptors within the F?rster radius,and thus shows high energy transfer efficiency around 80%in water.Moveover,it can be used as the ink to write multiclolor letters.