Preparation of Functional Microcapsules Consisting of Porous Polymer as Shell Material

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To obtain the functional microcapsules with a temperature-dependent release rate using in situ polymerization polystyrene microcapsules containing stearic acid as core material were prepared under the conditions of styrene monomer concentration = 2 - 6 mol/l and revolution rate of reactor paddle = 200 - 600 rpm. The following results were obtained from the release rate measurements with changing temperatures in the range of 293 - 343 K.1) A small effect of monomer concentration on microcapsule size was observed, that is, microcapsule size decreased with increasing monomer concentration. This would be due to that the viscosity decreases with monomer concentration and the comparatively rapid formation of polymer shell occurs from the phase separation in a short reaction time.2) The permeability coefficient of microcapsules decreased with increasing monomer concentration A_0 at the same temperature. This is the same as the permeability of many microcapsules prepared by in situ polymerization. Unit nuclear microcapsules were obtained for A_0 = 2 mol/l, microcapsules including many minute polystyrene beads for A_0 = 4 mol/l, and porous or multi-nuclear microcapsules for A_0 = 6 mol/l.3) Release rate of stearic acid at 75 ^ﾟC is about 15 times of that at 40^ﾟC, so the functional microcapsules, of which release rate us controlled with changing temperature, will be available with high possibility.