Preparation Of Monodisperse Fe₃O₄/PS Composite Microspheres

Magnetic polymer microspheres show significant potential application in bio-medical field due to diverse polymerization methods, various morphology and quickly response to external magnetic field. From investigation of literature thoroughly, magnetic polymer microspheres could be classified into five kinds of composite structures including core-shell structure, reverse core-shell structure, sandwich structure, inner-dispersed structure and hollow structure. Up to now, according the producing sequence of magnetic and polymer components, there are three synthesis routes to realize the above-mentioned five composite structures, which are (1) combination method of former-prepared magnetic nanoparticles and polymer, (2) in situ preparation of magnetic nanoparticles in the presence of polymer beads, (3) monomer polymerization method in the presence of magnetic nanoparticles. However, the preparation of magnetic polymer microspheres with uniform size distribution and high magnetization is always an existent issue left for further investigation, in that the simultaneous improvement of magnetic content and size distribution is quite a challenge.In this dissertation, based on the miniemulsion system, a novel hybrid emulsion polymerization was firstly developed in order to prepare monodisperse, high magnetite content polystyrene microspheres. With this aim in mind, we carried out the following research contents.1. By co-precipitation method, oleic acid modified magnetic Fe₃O₄ nanoparticles with magnetite content of 87.5 wt%, face-centered cubic structure and average size of 12nm were easily prepared. The as-synthesized Fe₃O₄ nanoparticles were dissolved into octane to form ferrofluid with the highest magnetite concentration up to 90 wt%. Then, one-step miniemulsion polymerization was used to synthesize Fe₃O₄/PS composite microspheres with size about 100nm and magnetite content of 50 wt%. The effect of surfactant amount and ultrasonic power was investigated.2. Carboxyl-functionalized magnetic polymer microspheres were synthesized by adding acrylic acid (AA) into one-step miniemulsion polymerization system. Fe₃O₄/P(St-AA) microspheres with size range of 41～163nm, magnetite content up to 78 wt% and surface carboxyl density of 0.058-0.25mmol/g were obtained. These kind of magnetic polymer microspheres are stable in the changed pH environment (pH=2～10). It was proved that the surface carboxyl density reached to saturation density when the addition amount of AA was 10 wt% (relative to St), the average size was decreased by increasing the amount of AA and surfactants, and magnetite content was controlled by changing ferrofluid amount.3. With the combination of stabilization principle in miniemulsion system and the initiation mechanism in emulsion polymerization, a hybrid emulsion polymerization was developed for synthesizing Fe₃O₄/polystyrene composite microspheres with monodispersity, size range of 50～200nm and high magnetite content over 80 wt%. The influence of various parameters on various aspects of the as-synthesized Fe₃O₄/polystyrene was investigated in detail: type of initiator on composite morphology, feed ratio of Mag-miniemulsion and St-macroemulsion on magnetite content, and hydrophobic agent or amount of surfactant on size and size distribution.4. Two-step miniemulsion polymerization was designed to prepare magnetic polystyrene with various morphology composite structure including spherical structure, red-cell structure, ring structure and crescent structure. The amount of hydrophobic agent (hexadecane) and kind of initiator have obvious effect on the microphase separation in polymerization process.