Synthesis, Modification And Application Of Polymeric Core-shell Microspheres

Core-shell structured microspheres have been fabricated via seeded emulsion polymerization. Hollow microspheres are prepared followed using the prepared core-shell structured microsphere as a precursor. The hollow microspheres are regarded as individual reaction containers, in which ZnO nanoparticles are synthesized in situ. In addition, surface modification on core-shell structured microspheres through graft polymerization is also investigated taking advantage of radiation initiation. The major work and related results include:1. PBA/PS and PMMA/PS core-shell structured microspheres are synthesized through seeded emulsion polymerization. Hollow microspheres are obtained followed with the core-shell microspheres as the precursors by acid-alkali swelling method. A variety of factors, which have influence on the morphology of core-shell and hollow structure, are studied. The results show that high instant conversion of monomers is the key factor to the formation of hollow structure at the stage of encapsulation. Temperature and drop speed of monomer and initiator are both significant to morpholoy control. Too low drop speed of second monomer phase can lead to the tanglement of polymeric chains between core layer and shell layer, which will hinder the formation of hollow structure. While too high temperature will result in the production of a large number of secondary particles (particles derived from bulk polymerizaiton). The nature of core monomer and shell monomer has also an impact on the morphology of hollow microsphere. The boundary between PBA core and PS shell is clearer due to its better hydrophobic nature compared to PMMA.2. PS hollow microspheres are prepared based on the above method. ZnO nanoparticles are produced in situ in the cavity of the hollow spheres. The morphology, UV-vis absorption, photoluminescence of the PS/ZnO nanoparticles,and the loading efficiency of ZnO are investigated. The swelling sequence of ZnO precursor, (CH3COO)2Zn·2H2O and LiOH·H2O, in the in-situ synthesis process of ZnO has great influence on the size of the ultimate particles, but little on the crystal form. The ratio of (CH3COO)2Zn·2H2O to LiOH·H2O has no impact on the size and crystal form. The UV absorption ability of ZnO nanoparticles has no relationship with the swelling sequence, whereas the photoluminescence property differs because the swelling sequence affects the size of ZnO nanoparticles, but photoluminescence depends on the size of the particles. 3. Investigation is made on the surface modification on PS/PBA copolymer microspheres through radiation graft polymerization. It is demonstrated that GMA can be grafted onto the surface of the copolymer microsphere under a total absorbed dose of 12.75 kGy at a dose of 24.4 Gy/min.