Preparation And Characterization Of Hollow Polymer Microspheres

Hollow polymer microspheres have excellent opacifying and deformation performances because of the special hollow structure and the refractive index difference between the shell polymer and the internal void. These outstanding performances bring hollow polymer particles into extensive applications, such as opacifing pigments, uvioresistant fillers, hand modifiers, etc. Nowadays, hollow polymer particles are widely used in coating, painting, paper making, leather treating, cosmetic, and so on. Such particles also have amazing potential applications as light weight agents, insulated agents, micro-capsule materials, etc. In this paper, the preparation and characterization of P(acrylate-styrene) hollow thermoplastic polymer microspheres were studied. Furthermore, the preparation process and hollow formation mechanism were experimentally and theoretically discussed.The first chapter summarized the manufacture methods of hollow polymer microspheres and their respective recent progresses. The advantages and disadvantages among various emulsion polymerization methods including alkali (acid) method, dynamic swelling method, SPG(Shirasu Porous Glass) emulsification technique, W/O/W emulsion polymerization and emulsion polymerization with encapsulation of a nonsolvent wereanlysized. Based on different mechanisms of templating polymerization——transcriptivesynthesis and morphosynthesis, the respective strengths and drawbacks of lay-by-lay(LBL) polyelectrolyte assembly on charged templates, templating polymerization on inorganic templates, templating polymerization on different types of surfactant (anion, cationic and anion/cationic) were compared. Finally, self-assembly method was briefly introduced.The second chapter intruduced the manufacture of hollow polymer microspheres using the alkali/acid method. P(methyl methacrylate-butyl acrylic acid-methacrylic acid) first-seed latex was prepared by emulsion polymerization. In order to extend the diameters of seed latex, second-seed latex was prepared by the first seeded emulsion polymerization. Finally, P(methyl methacrylate-butyl acrylic acid-methacrylic acid)/P(styrene- methacrylic acid) core-shell latex was prepared by the second seeded emulsion polymerization. Mentionably, pre-emulsification process was used in these emulsion polymerization proceduresmentioned above. Hollow polymer microspheres were obtained through treating the final core-shell latex in alkali/acid condition. The average diameters of hollow polymer microspheres with 30%~45% hollowness were controllable between 300nm~1200nm.The influences of acid monomer content, core/shell proportion and shell composition on the morphology of hollow polymer microspheres were investigated by means of TEM, FESEM and DLS. It was found that the suitable acid monomer content for the seed latex was between 30%~35% for obtaining complete hollow polymer microspheres with maximum hollowness. Furthermore, a matched co-relation existed between core/shell proportion and shell composition, i.e., at a certain core/shell proportion there was a corresponding shell composition for obtaining related maximal hollowness of polymer particles. The amount of monomers in the different stage of emulsion polymerization and the type of emulsifier are the most important factors to control the diameters of first-seed, second-seed and core-shell polymer particles.The formation mechanism of hollow polymer microspheres was discussed in this chapter. It was found that there were many fine pores existed on the surface of hollow polymer microspheres after the alkali treatment, and that the fine pores disappeared and the surface shell became smooth and compact in the following acid treatment. It explained that the fine pores arisen in the alkali treatment were the channels for alkali molecules to enter into core polymer, and that the surface shell was restructured under the acid treatment. Thus, the hollow formation at the alkali/acid treatment proceeded via the osmotic mechanism. The alkali molecules diffuse into carboxylated core polymer in the alkali t...