Ultrasonic generators are used As emulsifiers and as alternative initiators in polymerization processes. Styrene was polymerized under indirect ultrasonic irradiation in this study. It was thought that the effect of ultrasound on the polymerization changed over the course of the polymerization. The polymerization process was improved by changing the irradiation conditions in a manner appropriate to each stage of the polymerization. (c) 2007 Elsevier B.V. All rights reserved.