A Study Of The Theory And Application Of Radiation-induced Miniemulsion Polymerization

In this thesis,we successfully carried out miniemulsion polymerizations by(60)~Coγ-ray radiation initiation.Miniemulsion polymerization is an efficient way for producing nanoparticles,in which,it is just a one-to-one "copy" from monomer droplets to latex particles.By virtue of the characteristics of radiation polymerization, such as,simple system composing without additional initiator,temperature independence and the generation of free radicals in both the aqueous phase and monomer droplets,the application of miniemulsions can be extended to the preparation of polymer microparticles based on the theoretical studies.The main idea consists of six parts:(1) The characteristic of radiation miniemulsion polymerization. (2) Radiation miniemulsion polymerization with HTPB or its derivative as the costabilizer.(3) Graft copolymers of polyurethane with vinyl monomers via radiation-induced miniemulsion polymerization.(4) Preparation of styrene-alt-maleic anhydride copolymer from direct and inverse miniemulsion polymerization viaγ-ray radiation initiation.(5) One-step fabrication of polystyrene multihollow microspheres by radiation miniemulsion polymerization.(6) Emulsifier-free miniemulsion polymerization of styrene.The studies are described in detail as follows.1.The effect of Ostwald ripening on the particles' morphology in styrene/butyl acrylate miniemulsion copolymerization system was studied for the first time. Correspondingly,the monomer droplet stabilization mechanism of miniemulsion system was discussed.The experimental results indicated that the size of monomer droplets turned uniform after the 4.5 h's Ostwald ripening process and the droplets were stable during the polymerization.Or else,micrometer-sized "golf-like" balls had been prepared if the miniemlsion hadn't experienced an Ostwald ripening process. Additionally,with the increase concentration of the costablizer,the Ostwald ripening period shortened.Compared with the chemical initiated miniemulsion polymerization, the radiation miniemulsion polymerization method had been demonstrated to be more efficient.The reaction could take place at room temperature and the polymerization rate was accelarated.2.Polymeric costabilizer hydroxyl-terminated polybutadiene(HTPB) and its derivative polyurethane(PU) were successfully synthesized as the sole costabilizer in the miniemulsion polymerization of styrene initiated byγ-ray radiation.Compared with the classical emulsion polymerization and the miniemulsion polymerization costablized by hexdecane(HD) or cetyl alcohol(CA),the miniemulsion polymerization rate of miniemulsion polymerization with polymeric costablizer was much faster and the possibility of droplet nucleation was improved.In HTPB-costabilized miniemulsion system,high nucleation efficiency,96%,could be reached.On the other hand,in PU-costabilized system,polystyrene nanoparticles with relatively small diameter(40-70 nm) and narrow particle size distribution could be easily prepared.In the polymerization process,the instantaneous average free radical number in every colloid particle is even higher than 2.The effects of monomer, surfactant,costabilizer and absorbed dose rate on the miniemulsion polymerization rate and the particle size were discussed.3.Graft copolymers of polyurethane(PU) with various vinyl monomers were synthesized through a one-pot but two-step miniemulsion polymerization process. Firstly,PU dispersions were prepared using vinyl monomer as the solvent. Consecutively,an in-situ graft copolymerization of the vinyl monomers with the synthesized PU was initiated byγ-ray radiation at room temperature.The morphology of the graft copolymer was decided on the polarity of the monomer and the compatibility of PU with monomer.Compared to the seeded emulsion polymerization or chemical miniemulsion polymerization,the radiation miniemulsion polymerization method facilitated the preparation of homogeneous graft copolymers and the grafting efficiency had been improved greatly.4.Strictly alternating copolymer of styrene(St)-alt-maleic anhydride(MAn) (SMA) were successfully synthesized via direct and inverse radiation miniemulsion polymerization.Monodisperse core-shell structured particles had been fabricated in direct miniemulsions,with no dependence on the polymerization conditions.However, in inverse miniemulsion system,the weight ratio of dispersion phase and continuous phase,weight ratio of the two monomers,pH value of the miniemulsion and dose rate controlled the morphology of the final particles.If the polymerization was irradiated at a relatively low dose rate,"bean-like" particles would be fabricated due to phase separation.5.Instead of classical multi-step preparation of multiple emulsions,we develop a novel method to obtain a stable multiple emulsion from miniemulsion system.Due to the partition characteristic of nonionic surfactant,nonyl phenyl polyoxyethylene with an average of 10 ethylene oxides per molecule(OP-10),water/oil/water(W/O/W) structured monomer droplets could be formed.After irradiation byγ-ray,multihollow microspheres could be one-step fabricated if the content of pre-added polystyrene, which costablized the miniemulsion accompanying with CA,was in the region of 2-10 wt%based on the monomer.When the weight of polystyrene is 10%based on the monomer,the yield of multihollow particles can reach as high as 90%.6.A novel approach was realized to prepare monodisperse polystyrene(PS) particles via emulsifier-free miniemulison,which was stabilized by polystyrene oligomer,the decomposed KPS fragments and the costabilizer.The influential factors, such as,the category and amount of costabilizer,the pre-polymerization time and the content of initiator were studied.Compared with the conventional emulsifier-free emulsion polymerization,emulsifier-free miniemulsion polymerization proves to be a more efficient route to the fabrication of monodisperse smaller nanoparticles with narrower particle size distribution.