Effect of ultrasonic frequency on polymerization of styrene under sonication

The effect of ultrasonic frequency on polymerization of styrene under sonic ation at 50 degreesC was studied at the frequencies of 23.4, 45.7, 92, 518 kHz and 1 MHz. Polymerization under sonication was carried out at the ultra sonic intensity that gives the same reaction rate of decomposition of porph yrin. The magnitude of the polymerization rate increases in the order of 92 , 45.7 and 23.4 kHz. At the high frequencies of 518 kHz and 1 MHz, no polym erization was observed. These facts mean that there is an optimum frequency in the range from 92 to 518 kHz for effective polymerization. The average- number molecular weights at the sonication time of 3 h are 5.5 x 10(4), 8.0 x 10(4) and 11.5 x 10(4) for the irradiated frequencies of 92, 45.7 and 23 .4 kHz, respectively. Sonication for 3 h at 92 kHz gives polystyrene with v ery high polydispersity, about 5.0, in comparison with the results obtained at 23.4 and 45.7 kHz. These observations indicate that polymerization unde r sonication is influenced by the irradiated frequency. (C) 2001 Elsevier S cience B.V. Air rights reserved.