Precipitation of submicrometer-sized poly(methyl methacrylate) particles with a compressed fluid antisolvent

摘要

Submicrometer-sized poly(methyl methacry-late) (PMMA) particles were generated by precipitation with a compressed fluid antisolvent technique. The precipitation was carried out as follows. A solution containing PMMA was sprayed through a nozzle into a precipitator. The antisolvent CO_2 was continuously passed through the precipitator during the operation at a flow rate of 2000 mL/min. When toluene was used as the solvent, scanning electron microscopy images showed that solid, spherical PMMA particles with less coalescence could be generated only when both vapor and liquid CO_2 was present and the liquid CO_2 level in the precipitator was one-eighth. The morphology and size of the precipitated PMMA were found to be dependent on the solvents. Toluene, which had the lowest solubility parameter, was the most appropriate solvent in comparison with tetrahy-drofuran, acetone, and nitromethane. More uniform submi-crometer-sized PMMA particles were obtained at PMMA concentrations equal to or less than 1.0 wt in the toluene solution. A narrower particle size distribution was observed for precipitating PMMA with a molecular weight of 85,000 versus PMMA with a molecular weight of 36,000. To generate PMMA particles with less coalescence, liquid CO_2 instead of supercritical CO_2 was suggested for use in drying immediately after the spraying of the PMMA solution.