Fabrication Of Functional Polymer Microspheres With Controllable Shell

The synthesis techniques of mono-functional microspheres, such as monodispersed microspheres, magnetic microspheres, fluorescent microspheres, pH-sensitive microspheres and thermo-sensitive microspheres, etc., have been developed very well over the last two decades. Due to the quickly development of functional microspheres in many applications, including biotech, electro-tech, IT and new materials et al., the preparation of functional microspheres was shifted from mono-functional microspheres to multi-functional microspheres. In this thesis, several kinds of functional microspheres were prepared, and two different synthetic routes were chosen to fabricate the microspheres. For the first route, mono-dispersed microspheres were prepared as the core particles at first. After the surface of these microspheres being modified with functional group, the controllable polymerizations were carried out on the surface of the microspheres to synthesize functional polymers, so that the shell-functionalized core-shell microspheres were fabricated. For the second route, di-block copolymers were prepared firstly. Functional micromolecules or nanoparticles coordinated with the functional groups of the di-block copolymers to fabricated core-functionalized core-shell nanospheres. All the functional micro- and nano-size spheres were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and nuclear magneticresonance (NMR), etc. The main results have been obtained as follows:(1) Monodispersed sub-micron microspheres were prepared via two different soap-free emulsion polymerization, of which, methyl methacrylate (MMA) and glycidyl methacrylate (GMA) were used as monomer and divinyl benzene (DVB) was used as cross-linker. The un-crosslinked and low-crosslinked microspheres were synthesized by one-step soap-free emulsion polymerization. The high-density crosslinked microspheres were synthesized by two-step soap-free emulsion polymerization, in which the crosslinker were added into reaction system after the polymerization was initiated for a fixed amount of time. Owning to the different synthetic methods, the microspheres possess different shapes and structures.(2) To preparation of self-dispersible polymer microspheres with monodispersed size, monodisperse P(MMA-GMA) copolymer microspheres were utilized as core-particles and dendrimer PAMAM were acted as the functional shell. Dendrimer PAMAM grafted from the microspheres by repeated Michael addition and amidation. The core-shell functional microspheres with 7-generations PAMAM shell possess good self-dispersibility. Different cross-linking densities of core microspheres influence on the integrity of the functional core-shell spheres after acid treated. Protonated core-shell microspheres could load a mass of acid-modified magnetic nanoparticles.(3) Monodispersed sub-micron silica microspheres, as the core particles of the functional microspheres, were prepared via Stober process. Dendrimer PAMAM grafted from the silica spheres by repeated Michael addition and amidation. It is confirmed from FTIR and TGA results that the PAMAM were grafted onto the silica spheres successfully. The core-shell organic-inorganic hybrid microspheres were fabricated.(4) A series of poly(styrene-vinyl acetate) (P(St-VAc)) crosslinked monodispersed microspheres (240, 210, or 90 run) with different concentrations of PS (75, 50, or 25 wt %) were prepared by soap-free emulsion polymerization. Based on the crosslinked polymer microspheres, three series of monodispersed core-shell microspheres with pH-sensitive poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) shells weresynthesized by oxyanionic polymerization. Because the PDMAEMA chain could be protonated at a low pH, these core-shell microspheres could adsorb negative-charged magnetite particles, and at higher pH, the magnetite particles could be released again, this process was reversible.(5) Coordination-induced micelles were prepared via rare earth metal Eu(III) with block copolymer of PEG-b-PAA. Since PEG and PAA were all hydrophilic polymer, the micellization was induced by the coordination of Eu(III) with block copolymer in aqueous solution. Fluorescence spectroscopy showed the formation of coordinative complex by bond Eu(III) - carboxyl of AA. The coordinated micelles were formed with hydrophilic PEG blocks and hydrophobic coordinative complexes. A study of the dependence of emission intensities of the Eu-copolymers on the Eu content showed that the emission intensities increased nonlinearly with increasing Eu content. The acid modified quantum dot (QD) CdTe was also utilized to coordinate with the amino-group of block copolymer PEG-PDMAEMA in aqueous solution. The TEM images showed that core-shell fluorescence nanospheres were fabricated.