| 초록 |
During the early stages of the polymerization reaction of styrene, the large monomer-swollen latex particles tend to rise to the surface of the reaction vessel, or "cream", because during the first third of the reaction, the average density of the growing particle is less than that of the aqueous phase in which they are suspended. However, during the last two third of the reaction , the growing particles become heavier as more low-density monomer is converted to high-density polymer, and they tend to settle the bottom of the reactor. As the particles grow in successive seeding steps to diameters above 2~3 mm, the rate of creaming and settling become so rapid that it is not possible to keep them in suspension using conventional stirrer and still maintain their stability1,2. The gravitational effect of creaming and settling for the growing particles can also be eliminated by producing polymers with densities close to that of aqueous phase. In this case, the monomer concentration in the particle could be kept at the same level to ensure the density of styrene-swollen particle closer to that of water, using semi-continuous monomer addition process. The advantages of these processes include a convenient control of polymerization rate, particle morphology, and the composition in a copolymer system7-9, but the density control of polymerizing particles using monomer addition process has not been carried out yet. The mathematical model for the equal density polymerization system was developed to calculate the proper monomer feed rate based on both the material balance of the monomer for the total system and the knowledge of the polymerization kinetics.
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