Studies On The Self-assembly Based On Hyperbranched Polymers And Inclusion Complexation

Hyperbranched polymers are a novel kind of torispherical irregular macromolecules possessinghighly branched architectures, many inner cavities and a large amount of terminal functional groups.Due to their unique molecular structures and properties, hyperbranched polymers are receiving moreand more attention in self-assembly area. Among different kinds of driving forces leading toself-assembly, the host-guest inclusion plays an important role. Cyclodextrins (CDs) seem to be themost extensively studied host compounds characteristic of a hydrophilic exterior surface andhydrophobic interior cavity. It is well known that β-CDs form strong complexes with damantlygroups for their high association constant (~105), and this interaction has been widely employed inmacromolecular self-assembly. Our group has already got a great deal of experience in the theoreticalresearch, synthesis and self-assembly of hyperbranched copolymer. In this dissertation, investigationsare conducted on the self-assembly based on hyperbranched polymers and inclusion complexation. Thehost-guest interaction between β-CD and adamantine was introduced into the hydrophilic orhydrophobic hyperbranched polymer systems, and their self-assembly behaviors in solution wereinvestigated in details. In addition, the hierarchical self-assembly of hyperbranched polymers and theself-assembly of organic-inorganic nanoparticles based on inclusion complexation have also beenexplored. The main results are summarized as follows.1. The self-assembly of damantly-modified hyperbranched polyether HBPO-AD andβ-cyclodextrin;The damantly-terminated hyperbranched poly[3-ethyl-3-(hydroxymethyl)oxetane](HBPO-AD)was synthesized by combination of cationic ring-opening polymerization and end-group modification.Then the narrowly-distributed polymeric micelles were prepared via host-guest inclusion complexationand self-assembly of HBPO-AD and β-CD in aqueous solution. It was found that AD/β-CD molar ratio had a little effect on the micelle size and the size distribution.~1H NMR and TEM results proved that theobtained micelles hold a core-shell structure consisting of the HBPO-AD core and β-CD shell. Thesenarrowly-distributed HBPO-AD/β-CD micelles tended to be tightly packed into colloidal crystals, andcould further self-assemble into two-dimensional sheets in solution after thermal annealing. The TEM,SEM and AFM results demonstrated that the sheets were formed through stacking and fusion of tightlypacked HBPO-AD/β-CD micelles. The self-assembly mechanisms of HBPO-AD/β-CD micelles andtwo-dimensional sheets were proposed according to the detailed characterization results. TheHBPO-AD/β-CD micelles are formed due to strong hydrophobic interaction, inclusion complexationand hydrogen bonding. After heating, the solubility of micelles become weak in water and the micellestend to aggregate together. The thermal annealing temperature is higher than the glass transitiontemperature of HBPO-AD, which help the further fusion process of the tightly packed micelles to formtwo-dimensional sheets.2. The thermoresponsive property and self-assembly of damantly-modified hyperbranchedpolyglycerol;A novel thermoresponsive polymer based on hyperbranched polyglycerol (HPG) with adjustablelower critical solution temperature (LCST) was prepared via damantly-modification and inclusioncomplexation. HPG-Ads with the different graft ratios were prepared by esterification of HPG with1-adamantanecarbonyl chloride, and the T_gof obtained HPG-Ads increased almost linearly withincreasing the AD content. The HPG-AD showed concentration-dependent LCST phase transition inaqueous solution, and LCST increased gradually with the decrease of polymer concentration. Thethermoresponsive property and self-assembly behavior of HPG-AD were studied in detail by DLS,variable-temperature~1H NMR and TEM. It was found that HPG-AD self-assembled into largemultimolecular micelles in aqueous solution. The LCST transition was originated from the secondaryaggregation of the micelles due to the increased hydrophobicity of HPG-AD and the change ofhydrophilic-hydrophobic balance of HPG-AD on heating. In addition, the thermoresponsibility ofHPG-AD was highly related to the AD graft ratio. Only HPG-AD with a certain AD grafting couldshow a clear LCST. Moreover, the LCST transition could be adjusted via β-CD/AD inclusioncomplexation, and be controlled over a wide temperature range by changing β-CD/AD molar ratio.MTT method was also used to evaluate the cytotoxicity of HPG-AD, and it found that the introductionof damantly groups caused a greatly increase of the cytotoxicity, while its corresponding cytotoxicitycould be inhibited when β-CD was added.3. Synthesis, self-assembly and drug release property of HPG-g-PDMAEMA; A double-hydrophilic hyperbranched graft copolymer, HPG-g-PDMAEMA, was synthesized bycombination of cationic ring-opening polymerization and atom transfer radical polymerization.~1HNMR and GPC analyses showed that each HPG core was grafted3poly(2-(dimethylamino)ethylmethacrylate)(PDMAEMA) arms, with an average arm length of27. The pyrene-based fluorescentprobe method,~1H NMR, DLS and TEM were used to study the self-assembly behavior ofHPG-g-PDMAEMA in aqueous solution. It showed that HPG-g-PDMAEMA could form micelles inacidic, neutral and alkaline aqueous solution, which was different from the self-assembly behavior ofpH-sensitive linear double-hydrophilic block copolymers. The results of zeta potential proved thatPDMAEMA chains existed in the outer surface of the obtained HPG-g-PDMAEMA micelles.Coumarin102was used as a model drug to study the drug loading and releasing properties ofHPG-g-PDMAEMA under pH stimulation. It was found that HPG-g-PDMAEMA micelles couldcontinuously release and re-encapsulate the drug molecules when pH was continuously changedbetween11.5and2.5. However, this process was not totally reversible and the reversibility was relatedto the pH of the solution and the number of cycles. Since both HPG and PDMAEMA have goodbiocompatibility, HPG-g-PDMAEMA is expected to have potential applications in the fields ofmedicine and bioengineering.4. The hierarchical self-assembly of a crew-cut amphiphilic hyperbranched copolymerHBPO-star-PEO;A crew-cut amphiphilic hyperbranched multiarm copolymer, HBPO-star-PEO, was prepared bycationic ring-opening polymerization. This polymer could self-assemble into macroscopictwo-dimensional vesicle film in water, and the diameter of each vesicle could reach200μm. Throughreal-time observations by optical microscope, we found that the formation of the vesicle film was aninteresting hierarchical self-assembly process. The crew-cut HBPO-star-PEO molecules firstself-assembled into small vesicles, and then these small vesicles interconnected together as a result ofthe successive hydration and fusion to form the giant vesicle film. In addition, the complex of crew-cutHBPO-star-PEO and HBPO-star-PDMAEMA could also self-assemble into two-dimensional vesiclefilm, which further transformed into microtubes during the slow evaporation of solvent. Themorphology and formation process of microtubes were characterized by optical microscope, laserscanning confocal microscope, SEM and TEM. It showed that the diameter of these tubes was about2μm, and the length approached several damantly s. The transition mechanism from two-dimensionalvesicle film to microtubes was proposed according to the real-time observation results by opticalmicroscope. The small vesicles at the border of the large ones first fused into fiber-like structures. With the evaporation of the solvent, microphase separation occurred between HBPO-star-PEO andHBPO-star-PDMAEMA, and many new small vesicles were formed on the surface of the largevesicles. Then these small vesicles oriented orderly with fiber-like structures as templates and graduallyfused. Finally, the linear arrayed microtubes were formed.5. The self-assembly behaviors of damantly-modified POSS with β-cyclodextrin and itsderivatives;Adamantyl-modified POSS (POSS-AD) was synthesized by esterification of aminopropylisobutylPOSS with1-adamantanecarbonyl chloride. Then the self-assembly behaviors of POSS-AD with β-CD,hydroxypropyl-β-cyclodextrin (HP-β-CD) as well as water-soluble β-cyclodextrin-epichlorohydrincross-linked polymer (β-CDEP) in the toluene-water system were studied. It was found that POSS-ADcould induce β-CD self-assemble into thin films at the oil-water interface driven by the inclusioninteraction between β-CD and damantly groups. FT-IR and NMR analyses proved that the majorcomponent of this thin film was the inclusion complex of β-CD with toluene. Thus an interfaciallyinduced self-assembly mechanism of thin film was proposed. POSS-AD and β-CD formed a monolayerfilm at the oil-water interface as a result of inclusion complexation, which further induced thelayer-by-layer self-assembly of β-CD or β-CD/toluene inclusion complex into multilayer film due tothe strong hydrogen bonds of β-CD. In addition, POSS-AD and HP-β-CD could self-assemble intomicelles in aqueous phase after ultrasonic treatment, while POSS-AD and β-CDEP formed vesiclesunder the same conditions. These two different self-assemblies were characterized by TEM, SEM and~1H NMR, and it was found that POSS-AD/β-CDEP system could stabilize more toluene for theformation of vesicles.