Polyurea microcapsules containing a pyrethroid insecticide were prepared by the reaction between hexamethylene diisocyanate isocyanurate and ethylenediamine in an oil-in-water emulsion. This study was performed to establish the operational conditions of preparing microcapsules by interfacial polymerization and to investigate how the operational conditions affected the characteristics of microcapsules such as the morphology, wall thickness, mean diameter, and particle size distribution. Microcapsules prepared in this study were found to be spherical and monocore. The microcapsule yields, ranging from 94 to 98%, were almost equal to the theoretical values. The wall thickness of the microcapsules increased with the diameter of the microcapsules and the concentration of hexamethylene diisocyanate isocyanurate. In comparison with the results for microcapsules prepared with a mixture of hexamethylene diisocyanate uretidione and isocyanurate, the diameters and wall thickness of the microcapsules were found to be larger.

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To investigate the dependence of the shell thickness on both the microcapsule size and the concentration of hexamethylene diisocyanate (HMDI) and to analyze the chemical structure of the polyurea shell, polyurea microcapsules were prepared by using the reaction between HMDI uretidione/isocyanurate and ethylene diamine (EDA) in an oil-in-water emulsion. In the experiment, the concentrations of hexamethylane diisocyanate and EDA were changed. The shell thickness was correlated well with the mean size and the concentration of HMDI on the surface area per unit volume of microcapsule. From the solid-state 13 C NMR spectroscopy analysis, the uretidione and isocyanurate ring structures were found to be not changed before and after the reaction. From the wide-angle X-ray diffraction analysis, it was suggested that the chemical structure of the polyurea shell was amorphous. From the FTIR spectra analysis, it could be concluded that polyurea microcapsules were prepared by the reaction between HMDI uretidione/isocyanate and EDA.