Preparation And Application Of Hyperbranched Polyglycerol-Based Nanocomposites

Because of its excellent solubility, favorable biocompatibility, and abundant surface hydroxyl groups and interior cavities, hyperbranched polyglycerol (HPG) has become the "star macromolecule" in the field.of hyperbranched polymers, and has been widely studied in various fields such as biomaterials, drug delivery and release, catalyst support, polyelectrolyte and surfactant, and so on.On the basis of the combination of the features of HPG and inorganic nanomaterils that are being intensively researched, a series of novel and multifunctional HPG-based nanocomposites have been prepared in this dissertation. The applications of the resulting HPG-based nanocomposites were also explored. The detailed content is described as follows.(1) An in situ anionic ring-opening polymerization strategy was successfully employed to grow multihydroxyl HPG from surfaces of aqueous synthesized QDs directly, affording multifunctional CdTe@HPG nanohybrids. The grafted HPG content can be adjusted from 25 to 80 wt% by manipulating the feed ratio of glycidol monomer to QDs. The resultant CdTe@HPGs still showed strong fluorescence and good water-solubility, and could conjugate functional biomolecules (e.g., amino acids) with their multiple reactive hydroxyls. Cytotoxicity measurements revealed that the CdTe@HPGs were much less toxic than the pristine QDs in human lung cancer cells SPCA-1 and more grafted HPG leads to less toxicity, due to the envelope of biocompatible HPG on QDs. It was found that the pristine QDs were unstable and their fluorescence decreased greatly or was even completely quenched after 24 h in SPCA-1 cells, whereas the QD@HPGs still exhibited strong fluorescence. Furthermore, a facile one-pot strategy for synthesis of silica-hybridized CdTe quantum dots (SiO2-h-CdTe QDs) in aqueous solution was presented, and subkilogram-scale fluorescent SiO2-h-QDs can be readily produced in one batch. This approach also makes the tuning of emission wavelength and absorption bandgap of SiO2-h-QDs accessible for the first time. The resulting SiO2-h-QDs are ultrafine with diameters 8-16 nm, and show excellent optical properties, high stability, and versatile surface functionality compared with the neat QDs. With the silane hydroxyls as initiators, HPG can be facilely grafted from the surface of SiO2-h-QDs through in situ anionic ring-opening polymerization, affording SiO2-h-QD@HPG nanocomposites.(2) HPG was covalently grafted from the surfaces of hydroxyl-functionalized multiwalled carbon nanotubes (MWNT-OH) by the "grafting from" method based on in situ anionic ring-opening polymerization. The macroinitiator of MWNT-OH with hydroxyl density of 1.39 mmol per gram of nanotubes was prepared by one-pot nitrene chemistry. The amount of HPG grafted from MWNTs can be readily adjusted in a wide range by tuning the feed ratio of glycidol to MWNT-OH. The resulting HPG-grafted MWNTs (MWNT-g-HPG) nanohybrids were characterized by TGA, FTIR, and NMR spectroscopy, HRTEM, and SEM. The as-prepared nanocomposites showed good dispersibility in polar solvents such as water, DMF, and methanol. On the basis of numerous functional hydroxyl groups of the HPG grown on MWNTs, fluorescent molecules of rhodamine B were conjugated to the surface of MWNT-g-HPG by N, N'-dicyclohexylcarbodiimide (DCC) coupling, affording fluorescent MWNTs. Similarly, hydroxyl-functionalized carbon nanoonions (CNO-OH) were also facilely prepared by [2+1] cycloaddition of nitrenes. Then the HPG was also successfully grown on the surface of CNO-OH, affording CNO-g-HPG nanocomposites.(3) A versatile and robust adsorbent with both magnetic property and very high adsorption capacity was presented on the basis of functionalization of iron oxide-silica magnetic particles with carboxylic HPG (Fe3O4/SiO2/HPG-COOH). The structure of the resulting product was confirmed by FTIR spectra, TGA, zeta-potential, and TEM. According to the TGA results, the density of the carboxylic groups on the surface of Fe3O4/SiO2/HPG-COOH is calculated to be as high as 3.0 mmol/g, posing a powerful base for adsorbing dyes and drugs. Five kinds of dyes and one representative anti-cancer drug were chosen to investigate the adsorption capacity of the as-prepared magnetic adsorbent. The adsorbent shows highly efficient adsorption performance for all of the adsorbates especially for the cationic dyes and drug. The adsorption kinetics and isotherm of the adsorbents were investigated in detail and found that the kinetic and equilibrium adsorptions are well modelled using pseudo-second-order kinetics and Langmuir isotherm model, respectively. In addition, the influences of pH and ionic strength on the adsorption capacity were also examined and found that pH has much greater effect on the adsorption capacity compared with the ionic strength. Regeneration experiments showed that the Fe3O4/SiO2/HPG-COOH can be well regenerated in ethanol and partially regenerated in 1 M HCl aqueous solution. After regeneration, the magnetic adsorbents can still show high adsorption capacity even for 10 cycles of desorption-adsorption. No obvious decreases of magnetic intensity and aggregation of adsorbents can be observed even after 10 cycles of adsorption-desorption. (4) Fe3O4/SiO2/HPG-COOH was used as a robust magnetic support for noble metal nanocatalysts. With the use of the grafted-HPGs as templates, various noble metal nanocatalysts such as Pt, Au, and Pd were directly grown on the surfaces of magnetic support with ultrasmall and nearly monodisperse sizes and high coverage densities. Because of the amplification effect of HPG, high loading capacities of the nanocatalysts, around 0.296,0.243, and 0.268 mmol/g for Pt, Au, and Pd, respectively, were achieved. Representative catalytic reactions including reduction of 4-nitrophenol, alcohol oxidation, and Heck reaction demonstrated the high catalytic activity of the noble metal nanocatalysts. Because of the stabilization of HPG templates, the nanocatalysts can be readily recycled by a magnet and reused for the next reactions with high efficiencies.(5) A general strategy was discovered to to readily produce a large variety of nanocrystals such as noble metals, semiconductors, magnetic, rare-earth, and silver halides nanocrystals with uniform and small sizes, favorable biocompatibility, multiple functionality, good stability, and excellent solubility in both water and other polar solvents using multihydroxy HPG as stabilizer. The synthetic mechanism was also studied in detail by comparative investigating different concentration of metal ions and various polymer stabilizers with different molecular structures, molecular weights, and components. We found that the molecular structure and component are two key factors to prepare inorganic nanocrystals.