Metal-Free Atom Transfer Radical Polymerization For The Fabrication Of Organic-Inorganic Hybrid Functional Nanocomposites

Controlled free radical polymerizations (CRPs) represent one of the most far reaching developments in polymer design and synthesis, allowing facile access to functionalized polymers with controlled compositions and well-defined architectures. Among the controlled free radical polymerization techniques, atom transfer radical polymerization (ATRP) is arguably the most utilized and operates via a redox equilibrium process mediated by a ligated metal catalyst [i.e., Cu(I), Ru(II), Fe(II), etc.] to make all the initiating sites growing with same polymerization speeds for the polymers with well-defined structures. However, for a variety of applications, such as microelectronics, biomaterials, functional organic-inorganic hybrid nanocomposites, etc., a key limiting factor in using ATRP is metal catalyst purification and contamination. Although a significant focus for the ATRP field since the initial discovery has therefore been directed toward lowering catalyst loadings or removal of residual metals, it is still difficult to widely utilize traditional ATRP technique for the fabrication of functional organic-inorganic hybrid nanocomposites, and we envisaged that a much more viable and ambitious solution to this grand challenge would be the development of a metal-free catalyst system for atom transfer radical polymerization in the fields of functional polymers and organic-inorganic hybrid nanocomposites.In this dissertation, a series of functional block copolymers have been designed and synthesized by the metal-free atom transfer radical polymerization (ATRP), and then a series of organic-inorganic hybrid functional nanocomposites have been fabricated based on these functional block copolymers. The main results have been obtained as follows:1. Synthesis of multi-arm star-shaped diblock copolymers via the metal-free ATRP technique and their use as organic polymeric nanoreactors for the fabrication of core@shell CdSe@PMMA nanoparticles:A series of amphiphilic multi-arm star-shaped diblock copolymers (multi-arm star-shaped PAA-b-PMMA), composed of poly(acrylic acid) (PAA) as the first block, poly(methyl methacrylate) (PMMA) as the second block, and ?-cyclodextrin (P-CD) as core, with different molecular weights and the ratios of different blocks have been synthesized by the metal-free ATRP technique,10-phenylphenothiazine as the catalyst under 380 nm LED irradiation at room temperature for the sequential polymerization of tert-butyl acetate (tBA) and MMA monomers. After that, amphiphilic multi-arm star-shaped PAA-b-PMMA has been utilized as organic polymeric nanoreactors for the in situ fabrication of core@shell CdSe@PMMA nanoparticles, PMMA polymeric chains as shell capping on the surface of CdSe quantum dots. Owing to metal-free ATRP technique driven by light, the removal of residual metal has been avoided and the higher yield of copolymers can be obtained. The chain lengths of the first block PAA and the second block PMMA can be adjusted by tuning the LED irradiation time during the polymerization process for tuning the dimensions and sizes of CdSe quantum dots and PMMApolymeric shell.2. Fabrication of core@shell Au@PMMA hybrid nanoparticles via the metal-free ATRP technique:Firstly, the hydroxyl group of 4-amino-l-butanol was modified by the reaction between the hydroxyl group and 2-bromophenylacetyl bromide to prepare bi-functional ligands as the metal-free ATRP initiators. The precursors of Au (HAuCl4·4H2O) were reduced by amino groups of initiators to in situ fabricate Au nanoparticles with different sizes, and the surface of Au nanoparticles was capped with bi-functional ligands. Then MMA monomers were initiated to grow PMMA polymeric chains from the initiating sites on the surface of Au nanoparticles by the metal-free ATRP technique for the fabrication of core@shell Au@PMMA hybrid nanoparticles, composed Au nanoparticles as core and PMMA chains as shell with different sizes,10-phenylphenothiazine as the catalyst under 380 nm LED irradiation at room temperature. The dimensions of Au nanoparticles can be adjusted by changing the molar ratios of HAuCl4·4H2O to amino groups of ligands, and the thickness of PMMA polymeric shell can be tuned by adjusting the LED irradiation time during the polymerization process.3. Fabrication of core@shell superparamagnetic Fe3O4@PMMA hybrid nanoparticles via the metal-free ATRP technique:Firstly, the hydroxyl group of 12-hydroxydodecanoic acid was modified by the reaction between the hydroxyl group and 2-bromophenylacetyl bromide to prepare bi-functional ligands as the metal-free ATRP initiators, and then reacted with Fe2O3 to prepare precursors of superparamagnetic Fe3O4 nanoparticles. Superparamagnetic Fe3O4 nanoparticles with different sizes can be fabricated by in situ decomposition of precursors by using organic solvents with different boiling points, and the bi-functional ligands as the metal-free ATRP initiators capped on the surface of Fe3O4 nanoparticles. Then MMA monomers were initiated to grow PMMA polymeric chains from the initiating sites on the surface of superparamagnetic Fe3O4 nanoparticles by the metal-free ATRP technique for the fabrication of core@shell superparamagnetic Fe3O4@PMMA hybrid nanoparticles, composed superparamagnetic Fe3O4 nanoparticles as core and PMMA chains as shell with different sizes, 10-phenylphenothiazine as the catalyst under 380 nm LED irradiation at room temperature. The dimensions of Fe3O4 nanoparticles can be adjusted by changing the different organic solvents with different boiling points:higher boiling point for larger size of Fe3O4 nanoparticles, and the thickness of PMMA polymeric shell can be tuned by adjusting the LED irradiation time during the polymerization process. The resulting core@shell superparamagnetic Fe3O4@PMMA hybrid nanoparticles were then characterized by TEM, HR-TEM, XRD, EDS and SQUID.