Synthesis And Characterization Of Magnetic Spherical Polyelectrolyte Brushes

Magnetic polymeric sphere owns unique magnetic properties which could be widely applied in biochemical field. So more and more scientists pay much attention to and do various studies on it. Spherical polyelectrolyte brush is a core-shell structured microsphere with unique properties introduced by polyelectrolyte chains, such as pH-response and thermo-sensitivity. In this thesis, it is the first time to introduce magnetic nanoparticles into spherical polyelectrolyte brush (SPB) which broadens the applications of SPB. There are two methods to magnetically functionalize SPB:(1) SPB could perfectly concentrate counterions, so it is considered as an ideal nano-reactor to synthesize magnetic nanoparticles which not only solves the problem of instability, even aggregation resulting from large surface-area-to-volume ratio with particle size decreasing, but offers a stabilized carrier for further application of nanoparticles. (2) Encapsultion of magnetic nanoparticles into the SPB core to enhance the saturation magnetization which leads to quick magnetic response.Based on SPB nano-reactor, we successfully synthesized magnetic nanoparticles with the controllable size and configuration under mild experimental conditions. The magnetic spherical polyelectrolyte brush (MSPB) had excellent stability and the properties of spherical polyelectrolyte brush were not changed by magnetic nanoparticles in the brush layer. The "nanoreactor" method offered a new way to prepare ultra-sized metal oxide nanoparticles. Meanwhile due to the unique properties of well-arrayed magnetic nanoparticles in MSPB, it could be foreseen the use of MSPB in high-efficient catalysis, or computational model to study the theories. On the other hand, through miniemulsion polymerization route, Fe3O4 nanoparticles were encapsulated in PS core and later UV light initiated the photoemulsion polymerization to graft PAA brushes. The spherical polyelectrolyte brush containing magnetic core (SPBM) owned superparamagnetic properties which could be taken advantage of to separate SPB with the aid of strong magnet. SPBM nanocomposites could be used for novel magnetic memory material, removal of poisonous heavy metal ions in waste water or controllable release of drugs.This thesis focused on the synthesis and characterization of these two kinds of magnetic composite spherical polyelectrolyte brushes (MSPB and SPBM) through different methods and main work as follows: 1. SPB was synthesized via combination of mini-emulsion polymerization and photoemulsion polymerization. First, the PS core particle was prepared by miniemulsion polymerization, at the end of which the photo-initiator HMEM was added in to the system. Under UV light initiation, PAA chains were chemically grafted to the core particles. The hydrodynamic diameter of as-prepared SPB was about 100nm. Magnetic nanoparticles were prepared through co-precipitation method using SPB as nanoreactor. The final product was MSPB with 1-3nm magnetic nanoparticles in the brush layer. MSPB owned good stability. The magnetic nanoparticles were combined with carboxylic groups through chemical bond called bidentate chelating. MSPB kept the same brush behavior at different pH value and ionic strengths. Collective behavior which appeared as transition from superparamagnetism to ferromagnetism of MSPB was showed due to dipole-dipole interaction between adjacent magnetic nanoparticles.2. The shape, size and crystallinity of as-prepared magnetic nanoparticles in SPB nano-reactor were largely determined by three factors:confinement of SPB, alkalinity of the latex environment and ion exchange. In the experiments, different configurations of nano-reactor and preparation routes were adopted to explore the influence on nucleation and growth of magnetic nanoparticles.3. The hydrodynamic diameter of SPBM microsphere was about 150nm. Magnetite content of core could be modulated by ratio of magnetic nanoparticles to monomer. The highest magnetite content in this work was 55wt.%. It was found that higher magnetite content led to lower core monomer conversion rate. Oleic acid surface-modified magnetic nanoparticles had good compatibility with styrene however almost incompatible with polystyrene. So phase separation between magnetic nanoparticles and PS happened (segregation) which negatively affected later encapsulation of photo-initiator and decreased productivity of PAA grafting. DVB was introduced as crosslinker to prevent segregation.4. SPBM was superparamagnetism. The magnetic response rate could be controlled by modulating magnetite content and pH value of latex. Higher magnetite content and lower pH value were favorable to accelerate magnetic collection of SPBM. In the thesis, magnetic properties were firstly combined to SPB. The creative ideas in detail are illustrated as follows:(1) Ultrafine magnetic nanoparticles with the size of less than 5nm were synthesized in SPB nanoreactors. The composite particles had excellent stability and unique magnetic properties. (2) Size, size distribution and magnetic content could be modulated through different feeding sequences and nanoreactor configurations which offered a noval method to synthesize magnetic nanoparticles.(3) Encapsulation of magnetic nanoparticles in SPB core made SPBM superparamagnetic which could quickly respond to strong magnet. The new magnetic composite particles could be used in recycling of SPB which extend the potential applications of SPB.