Application Of Hyperbranched Polymers In The Preparation And Self-assembly Of Nanocrystals

Hyperbranched polymers are a kind of highly branched polymers with three-dimension topological structures. They have many inner cavities and a large amount of terminal functional groups. Due to their unique molecular structures and facile synthsis route, hyperbranched polymers have received much attention and remarkable development has been made on their synthesis, characterization and modification in the passed decades. This leads to an increasing interest on the application of hyperbranched polymers, such as the molecular self-assembly, the control-release of medicine, nanoparticle encapsulation, gene transfection, and so on. Howerver, there are still a lot of areas to be explored and improved. In this dissertation, some new researches on the application of hyperbranched polymers have been made: (1) We synthesized hyperbranched poly(amidoamine) (HPAMAM) via the AB+Cn strategy and prepared various nanoreactors based on chemical modification or non-covalent interactions to synthesize CdS quantum dots (QDs) and Au, Ag metal nanocrystals (NCs); (2) Hyperbranched poly(ethylenimine) (HPEI) was used to in situ prepare magnetic nonviral gene vectors and the magnetization properties was also investigated; (3) The CdTe and Au NCs encapsulation by amphiphlic HPAMAM and the self-assembly of CdTe and Au NCs at the water/chloroform interface were realized, respectively. The details and main conclusions are described as follows:1. Preparation of Nanocrystals within Hyperbranched Polymer NanoreactorsHyperbranched poly(amidoamine) (HPAMAM) with ester groups was synthesized and used as nanoreactors to prepare CdS quantum dots (QDs) with small particle size and low size-distribution. The effects of molar ratio of Cd2+/S2-, reaction temperature, pH value in the reactions and aging time on the photoluminescence of CdS QDs were investigated. The resulting CdS/HPAMAM nanocomposites were then characterized by UV-Vis, PL, TEM and FT-IR. 2. A New Two-phase Route to Nanocrystals Using Amphiphilic Hyperbranched Polymers as Unimolecular NanoreactorsA new two-phase route has been developed to prepare monodisperse CdS QDs. In a two-phase system, chloroform and water were used as separate solvents for palmitoyl chloride functionalized hyperbranched poly(amidoamine) (HPAMAM-PC) and cadmium acetate/sodium sulfide, respectively. The amphiphilic HPAMAM-PC with a hydrophilic dendritic core and hydrophobic arms formed stable unimolecular micelles in chloroform and was used to encapsulate aqueous Cd2+ ions. After reaction with S2- ions from aqueous phase, monodisperse CdS QDs stabilized by HPAMAM-PC unimolecular micelles were obtained. Au and Ag nanocrystals smaller than 2 nm were also prepared by this method.3. Preparation of Nanocrystals within Supramolecular Self-assembly Nanoreactors and their Phase Transfer BehaviorA new strategy for the synthesis of CdS QDs within supramolecular self-assembly nanoreactors has been described. The self-assembled nanoreactors were readily constructed through the electrostatic interactions and ion pairs between palmitic acid and the terminal amine groups of hyperbranched polymer. In a chloroform/water two-phase system, aqueous Cd2+ ions were spontaneously encapsulated into the cavities of self-assembly nanoreactors in chloroform. After reaction with S2- ions, the CdS QDs with high stability were obtained. By the addition of excess triethylamine, CdS QDs formed in the self-assembly nanoreactors were transferred from organic phase into aqueous phase. After dialysis and rotorary evaporation, aqueous CdS QDs could be redispersed into chloroform solution containing palmitic acid.4. In situ Preparation of Magnetic Nonviral Gene Vectors and Magnetofection in VitroA new route to in situ preparing magnetic nonviral gene vectors in the form of organic/inorganic hybrids was realized. The magnetic nonviral gene vectors were prepared in the presence of ferrous salts and HPEI with different molecular weights. HPEI, one of the most promising nonviral vectors, was not only utilized as the nanoreactors and stabilizers to prepare magnetic nanoparticles, but also skillfully used as a base supplier to avoid introducing alkali hydroxide or ammonia. Magnetic nonviral gene vectors with various magnetite contents and saturation magnetizations were gained by changing the weight ratio of HPEI to FeSO4·7H2O and the molecular weight of HPEI. MTT assays suggested that the resulting magnetite/HPEI gene vectors had lower cytotoxicity compared with pure HPEI. The magnetite/HPEI nonviral gene vectors were used for magnetofection. It was found that the luciferase expression level mediated by magnetite/HPEI in COS-7 cells under a magnetic gradient field was approximately 13-fold greater than that of standard HPEI transfection in the best case.5. Self-assembly of Nanocrystals at the water/oil Interface by Amphiphilic Hyperbranched PolymersA general strategy for realizing the self-assembly of aqueous CdTe and Au NCs at the water/oil interface by means of amphiphilic core-shell hyperbranched polymer has been proposed. In the case of CdTe NCs, for example, aqueous CdTe NCs were firstly transferred into chloroform phase in the presence of palmityl choloride functionalized hyperbranched poly(amidoamine) (HPAMAM-PC), and then self-assembled at the water/chloroform interface by decreasing the pH value of aqueous phase or introducingα-cyclodextrins (α-CDs) to the aqueous phase. The resulting CdTe/HPAMAM-PC self-assembly film was characterized by fluorescence microscopy, UV-Vis, PL, TEM, EDS, FT-IR, DSC and TGA.In conclusion, based on hyperbranched polymers, different kinds of nanoreactors were prepared by chemical modification or non-covalent interactions and used to synthesize CdS QDs, Au and Ag NCs. Magnetic NCs were in-situ prepared within HPEI nonviral gene vetors and their magetofection properties were investigated. The self-assembly of CdTe and Au NCs was also realized by amphiphilic hyperbranched polymers. These NCs/hyperbranched polymer hybrid materials may provide important informations to the applications of hyperbranched polymers and NCs.