Abstract
If water is irradiated by strong ultrasound, radicals (OH・, H・etc.) are generated due to the collapse of the cavitation bubbles. These radicals can be used as initiators of radical polymerization using ultrasound. As the polymerization progresses, however, increase of the polymer concentration may affect the generation of the bubbles. In this study, aqueous solutions of polyethylene glycol (PEG) with various concentrations were sonicated and the MBSL was measured by a photo counter, and the radical generation was measured by ESR. If PEG of Mw=2×10^6was used, the initial generation rate of radicals decreases as the concentration of PEG increases. As the sonication time increased, radical generation rate and MBSL decreased and disappeared at about 1OOmin. GPC date of the sonicated sample showed that the molecular weight of PEG has decreased to about 104. If PEG of Mw=2×10^4 was used, MBSL and radical generation were not observed at all. These date suggest that PEG molecules of molecular weight of the order of 10^4 suppress the formation of cavitation bubbles.
