| The rapid expansion of supercritical solutions (RESS) is a novel process preparing micro-particles,which has been developed in the recent years. The purpose of this thesis was preparing the paraffin wax micro-particles, polymethyl methacrylate (PMMA) micro-particles, and nylon 6,6 micro-particles through the technology of the rapid expansion of supercritical solutions, used the supercritical carbon dioxide as the solvent. The raw material PMMA was prepared independently by solution polymerization, and controlled its relative molecular mass by means of controlling the amount of the initiator.The influence of the temperature, the pressure in the cauldron, the spray nozzle's temperature, and the extraction time had been investigated thoroughly during the RESS process of three different materials. The sizes and the appearances of the obtained micro-particles had been analyzed by means of Scan Electron Microscope (SEM) and Transmission Electron Microscope (TEM).The results show that the sizes of paraffin wax micro-particles are between 5μm and 10μm, the appearances of these mirco-paticles are irregular, and they reunite severely; the sizes of the PMMA and nylon 6,6 micro-particles are between 100nm and 500nm, they show regular appearances, which are sphericity, and they reunite slightly. All of three kinds of materials micro-particles'sizes reduce along with the increase of the cauldron pressure. The influences of the temperature are more complex: the sizes of paraffin wax micro-particles increase along with the increase of the temperature; the PMMA micro-particles'sizes decrease along with the increase of temperature; the structure of the products of nylon is fibrous. Besides, the temperature of spray nozzle has different influences on three kinds of materials: the sizes of paraffin wax and nylon 6,6 micro-particles decrease, when the temperature of spray nozzle increases; the PMMA micro-particles'sizes change little along with the increase of the temperature of spray nozzle.
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