Development of Highly Precise Controlling Methods for Polymer Microspher by Taking Advantage of Nonlinear Dynamics

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This research attempted to take advantage of the nonlinear dynamics in continuous emulsion polymerization processes in order to control latex particle size distribution. When the emulsion polymerization of vinyl acetate was conducted in a CSTR under conditions below the critical micelle concentration of the emulsifier, the monomer conversion attained in a time-independent steady-state operation showed a drastic rise from 0 to over 60% at a critical reaction temperature or mean residence time. The mean residence time or the reaction temperature was switched alternately between two values in the non-steady-state operation, one giving zero monomer conversion and the other a high monomer conversion in the usual steady-state operation. The periodic-switching operation induced oscillations in monomer conversion in time. The particle size distribution varied synchronously with the switching operation. This research showed the possibility of controlling the particle size distribution by adjust … More ing the frequency and/or the amplitude of the temporal variation of the mean residence time or reaction temperature. This research found that even while the constant monomer conversion was maintained at the steady state, the particle size distribution oscillated with a very large time period. This research revealed that the oscillations occur by a competitive interaction between polymerization reaction and aggregation of latex particles. In order to vary the colloidal stability of latex particles, a nonionic surfactant was added in some cases. It was found that using a mixture of a nonionic surfactant and an anionic surfactant was very effective for suppressing the oscillations. In order to take advantage of the oscillations of particle size, emulsion polymerization of vinyl acetate was performed in a system of two continuous stirred tank reactors in series. The oscillatory behavior could be controlled by varying the rotational speed of the impeller and the mean residence time. The research using two CSTR in series indicated the possibility of producing various poly-dispersed latex particles. Less