پليمريزاسيون به كمك امواج فراصوت

Ultrasonically initiated polymerization

Ultrasound consists of high-frequency sound waves and is widely used in medical purposes and chemical reactions, especially polymerization. The emulsion polymerization of some monomers can occur without the conventional free radical initiators under ultrasonic irradiati on. In this paper recent experimental results are reviewed in three sections: (1) nature and source of the free radical fo r the initiation process; (2) effects ofdifferent types ofcavitation; and (3) dependence ofthe p olymerization rate and the p olymer molecular weight on acoustic intensity, inert gas flow rate, typ e ofsurfactant and its concentration, and initial monomer concentration. Since the polym eriza tion ofmonomer and degradation ofpolymer occur simultaneously, the ultrasonically initiated emulsion polymerization is complicated. The experimental results show that ionic surfactants play a very important role in obtaining a high polymer yi eld, and high conversions can be reached in a short time with usage of a high purge rate ofN2. An increase in ultrasound intensity leads to an increase in polymerization rate in the rang e ofcavitation threshold and cavitation peak values. Lower monomer concentration favors enhancement of polymerization rate