| The preparation and release technology of microcapsule which could be controlled release periodically and slowly had great theoretical and practical applicable value in many industrial areas, such as drug delivery, catalyst, gel breaker, phase-change material, buffer, pesticide, adhesion and self repair materials. This essay was aimed to prepare ammonium sulfate (APS) microcapsules that could be controlled release periodically and slowly (it could be used as the gel breaker of oil production) and discuss the mechanism of its formation and control release. The several aspects of specific work were as follows:(1) APS microcapsule which could be controlled release periodically and slowly was made up of solid APS particles and polypyrrole (Ppy) and successfully prepared by in situ polymerization. Through a series of characterization methods (transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM), optical microscope (OM), Fourier transform infrared spectra (FTIR), X-ray powder diffraction (XRD), thermogravimetric analyzer (TGA) and conductivity meter, etc), microcapsule’s internal and surface morphology, thickness of shell, dispersion, chemical composition, thermal stability and controlled release properties have been studied. The formation and controlled release mechanism of APS microcapsule on the basis of this were also raised. The results of study on the storage stability of the microcapsule suggested that it could be well dispersed in water and the size did not change significantly after storage for 6 months at room temperature. So, this method was suitable for the preparation of microcapsule that could be stored for a long time. How the thickness and composition of shells and temperature affect the release behaviors of microcapsule in water was studied. The results showed that the release time of microcapsule could be controlled by regulating the concentration of glycerol monomer, temperature or the shell thickness.(2) A novel evaporation-dispersion-polymerization was presented to prepare microcapsules composed of APS as core and P(St-co-MMA) copolymer as shell. The APS could be controlled burst release from the prepared microcapsules. Average size of the microcapsules about 10-16 μm, the outer surface of microcapsule shell was covered with a layer of nanometer particles (50～100 nm), and the density was high. Through the study of the storage stability of the microcapsule, the result revealed that the microcapsules stored at room temperature; after 5 months, its shape, dispersion and controlled release performance substantially kept the same, which showed that the microcapsules prepared by the method had good storage stability and it met the basic requirements of industrial application. The controlled release behavior of microcapsule was studied at different temperature, pH and NaCl concentration, the study showed that core material in microcapsules could be controlled burst release, and its initial release time could be regulated by adjusting the temperature and NaCl concentration. In addition, sodium nitrite microcapsules with the property of controlled burst release could be successfully prepared by evaporation-dispersion-polymerization; the results showed that the method had a certain generality, providing the theoretical guidance for other types of microcapsule preparation.(3) On the basis of evaporation-dispersion-polymerization method, the emulsion-evaporation-polymerization method was proposed to prepare microcapsules composed of APS emulsion as core and P(MMA-co-AA) copolymer as shell. The APS microcapsules could be prepared by the method confirmed with the burst release property by a series of characterization, and the formation mechanism of the microcapsules was proposed. The controlled release properties of the microcapsules were studied in water, and the results showed that within a certain period of 8 to 32 hours, the core material of the microcapsule could be controlled burst release from the microcapsules, and the time of its initial release could not only adjusted by the temperature and salinity of the water, but also by pH value of the water and shell thickness of microcapsules. By OM and FE-SEM characterization methods, the releasing process of the microcapsules was observed. The results showed that the size of microcapsule grew by swelling, the shell thickness of microcapsule became thinner with the increasing time of microcapsules in the hot water, when the swelling degree of the shell material exceeded a certain range, the core material of the microcapsules could be controlled burst release from the microcapsules timely, on this basis, the mechanism of controlled release of the microcapsules was proposed.(4) Microcapsules with PMMA/Ppy composite shell type was successfully synthesized by in situ polymerization. Water-soluble APS was first modified to be hydrophobic particle, then above particles were as the cores of microcapsules. Through the hydrophobic modification of APS particles surface by oleic acid and silane coupling agent, the study showed that through the modification of the two modified materials, the hydrophobicity of APS have been significantly improved; the hydrophobicity of APS modified by the silane coupling agent was better than hydrophobicity of APS modified by oleic acid. By comparing the water solubility of the two modified APS, the reaction mechanism of oleic acid and silane coupling agents reacted with APS were proposed. By FE-SEM, FTIR, XRD, TGA and other methods for characterization of microcapsules, the result showed that APS was alternately wrapped by Ppy and PMMA. and monolayer PMMA/PPy composite shell. The property of APS particals never changed after microcapsulation. The release properties of the composite shell microcapsules was studied under different conditions, such as temperatures, pH, and shear forces. The result showed that the microcapsules prepared by this method also had the burst release behavior, and its property was only affected by temperature, regardless of pH and shear forces.
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