Synthesis Of PEO/PAA Star-Shaped Brush-Like Copolymers And Preparation Of Inorganic Functional Nanocrystal Clusters With Organic Polymeric Unimolecular Templates

Multi-arm star-shaped brush-like copolymers 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, comparing with the linear analogues, star-shaped brush-like polymers exhibit high solubility in common solvents, low viscosity, and modified thermal properties. In addition, copolymer brushes have also received increasing attentions due to their unique chemical and physical properties, especially for fabrication of inorganic functional nanomaterials which are widely applied in many different fields, such as magnetic assembly, magnetic resonance imaging, drug delivery, photo-catalysis, light-emitting diodes, and so on. In this dissertation, a series of poly(ethylene oxide)/poly(acrylic acid) (PEO/PAA) double-hydrophilic multi-arm star-shaped graft block copolymers based on a-cyclodextrin(a-CD) as core have been synthesized by a combination of anionic copolymerization and atom transfer radical polymerization(ATRP), and used as organic polymeric unimolecular templates to prepared spherical ferroferric oxide(Fe3O4) nanocrystal clusters, one-dimensional(1D) colloidal Fe3O4 nanocrystal clusters and cadmium selenide(CdSe) colloidal nanocrystal clusters respectively. These work has not been report yet. Our analytic works in concrete:(1) Synthesis of a series of novel water-soluble multi-arm star-shaped graft block copolymers based on a-CD as coreTwo kinds of novel structure PEO/PAA water-soluble multi-arm star-shaped graft block copolymers based on a-cyclodextrin as core have been synthesized by a combination of anionic copolymerization and atom transfer radical polymerization (ATRP). Meantime, the resulting products were then characterized by gel permeation chromatography(GPC), fourier translation infrared spectroscopy(FT-IR), hydrogen-nuclear magnetic resonance(1H-NMR). The structures of these multi-arm star-shaped graft block copolymers are in accord with the molecular structure that we designed. The first compolymer was double-hydrophilic multi-arm star-shaped brush-like block copolymer (PEO-g-PAA)-b-PEO, composed of PEO as the main chain, PAA as functional graft chains, and a second PEO block as the shell. The second one was double-hydrophilic multi-arm star-shaped brush-like copolymers with different molecular weights using a-cyclodextrin as a multifunctional initiator, double-hydrophilic multi-arm star-shaped brush-like copolymer PEO-g-PAA, which consisted of PEO as the main chain and PAA as functional side chains. Two kinds of double-hydrophilic multi-arm star-shaped brush-like copolymers are water-soluble and the molecular weight distributions are low(PDI= 1.08?1.18).(2) Preparation of superparamagnetic spherical Fe3O4 colloidal nanocrystal clusters using water-soluble multi-arm star-shaped brush-like block copolymers (PEO-g-PAA)-b-PEO as unimolecular micelle templateMulticompartment unimolecular micelle templates were firstly prepared based on a novel water-soluble multi-arm star-shaped brush-like block copolymers (PEO-g-PAA)-b-PEO, with different molecular weights and grafting density, and then FeCl3 and FeCl2, as precursors of Fe3O4, were loaded into graft chain PAA domain of multi-arm star-shaped brush-like block unimolecular micelle template, by coordination interaction between precursors and carboxyl groups of PAA domain, followed by an in situ reaction to form Fe3O4 colloidal nanoclusters. The resulting multicompartment unimolecular micelle templates and Fe3O4 colloidal nanocrystal clusters were then characterized by transmission electron microscopy(TEM), high-resolution transmission electron microscopy(HR-TEM), dynamic light scattering(DLS), atomic force microscope(AFM), X-ray diffraction(XRD), energy dispersive spectrometer(EDS), superconducting quantum interference device(SQUID). TEM characterization shows that the average diameter of unimolecular micelle template was 42±4.6nm, the average diameter of spherical Fe3O4 nanocrystal clusters (the aggregates of small primary Fe3O4 colloidal nanocrystals) is 30±3.2nm. The dimensions of Fe3O4 primary nanocrystals can be adjusted by changing molar ratio of precursors to PAA repeating units. When the molar ratios of Fe3O4 precursors to AA units in PAA domain was 2:1, the average diameter of Fe3O4 nanocrystal was 3.6±0.4nm, and the mole ratio increased to 6:1, the average diameter of Fe3O4 nanocrystal increases to 7.6±1.4nm. The Fe3O4 colloidal nanocrystal clusters show superparamagnetic behavior at room temperature and are highly water-dispersed.(3)Synthesis of 1D colloidal superparamagnetic Fe3O4 nanocrystal clusters via a combination of magnetic assembly with photo-induced cross-linking using water-soluble multi-arm star-shaped brush-like block copolymers (PEO-g-PAA)-b-PEO as unimolecular micelle templateDouble-hydrophilic multi-arm star-shaped brush-like copolymers PEO-g-PAA with different molecular weights and grafting density, as spherical unimolecular micelle template was utilized to structure-direct the in suit formation of spherical Fe3O4 colloidal nanocrystal clusters, by loading precursors of Fe3O4(FeCl3 and FeCl2) into the PAA compartment. Sequentially, surface-tethered PAA grafting chains of Fe3O4 colloidal nanocrystal clusters, produced by ATRP, retain terminal bromine atoms that were subsequently converted into photo-cross-linkable azide groups(-N3) as functional chain-end groups through nucleophilic substitution. The spherical Fe3O4 colloidal nanocrystal clusters coated with photo-cross-linkable azide groups were assembled into temporary 1D colloidal Fe3O4 nanocrystal clusters by exposure to external magnetic fields. The resulting temporary 1D Fe3O4 colloidal nanoclusters were efficiently photo-induced cross-linked by exposure to UV light to stabilize the 1D Fe3O4 colloidal nanocrystal clusters. The resulting unimolecular micelle templates, introduction of -N3, spherical Fe3O4 colloidal nanocrystal clusters and 1D Fe3O4 colloidal nanocrystal clusters were then characterized by TEM, HR-TEM, FT-IR, AFM, XRD, EDS, SQUID. TEM shows that the average diameter of unimolecular micelle template was 24±2.6nm, the average diameter of spherical Fe3O4 colloidal nanocrystal clusters were 21±2.9nm, and the average diameter of spherical Fe3O4 nanocrystal was 3.8±0.5nm, and these spherical colloidal nanocrystals were uniform size. The dimension of the resulting stable and crosslinked 1D Fe3O4 colloidal nanocrystal clusters can be tuned by adjusting the strength of external magnetic field. The stronger the magnetic field strength, the longer and thicker the nanowire. However, the magnetic field strength is too small or too large to get 1D Fe3O4 colloidal nanocrystal clusters. 1D Fe3O4 colloidal nanocrystal clusters show superparamagnetic behavior at room temperature and are highly water-dispersed.(4) Fabrication of CdSe colloidal nanocrystal clusters based on the water-soluble star-shaped brush-like block copolymers (PEO-g-PAA)-b-PEO as multicompartment unimolecular micelles templateMulticompartment unimolecular micelle templates were firstly prepared based on a novel water-soluble multi-arm star-shaped brush-like block copolymers (PEO-g-PAA)-b-PEO, with different molecular weights and grafting density. And then NaHSe and Cd(acac)2, as precursors of CdSe, were loaded into graft chain PAA domain of multi-arm star-shaped brush-like block unimolecular micelle template, by coordination interaction between precursors and carboxyl groups of PAA domain, followed by in situ reaction to fabricate CdSe colloidal nanocrystal clusters. The resulting multicompartment unimolecular micelle templates and CdSe colloidal nanocrystal clusters were then characterized by TEM, HR-TEM, AFM, XRD, EDS, SQUID, UV-Vis, Spectrofluorophotometer. TEM shows that the average diameter of spherical CdSe colloidal nanocrystal clusters composed of primary CdSe quantum dot and the primary CdSe quantum dot were 29±3.3nm,3.2±0.3nm respectively, and they were uniform size. CdSe colloidal nanocrystal clusters was highly water dispersible and the aqueous solution of CdSe colloidal nanocrystal clusters emitted green fluorescence under UV illumination.