| Abstract: | The ultrasonic degradation of poly(vinyl acetate) (PVAc) solutions was carried out in dioxan at 25, 30, 35, 40, and 45 °C to investigate the effects of the temperature and solution concentration on the rate of degradation. The kinetics of degradation were studied by viscometry. The calculated rate constants indicated that the degradation rate of the PVAc solutions decreased as the temperature and solution concentration increased. The calculated rate constants were correlated in terms of the concentration, temperature, vapor pressure of dioxan, and relative viscosity of the PVAc solutions. This degradation behavior was interpreted in terms of the vapor pressure of dioxan, the viscosity, and the concentration of the polymer solutions. With increasing temperature, the vapor pressure of the solvent increased, and so the vapor entered the cavitation bubbles during their growth. This caused a reduction in collapsing shock because of a cushioning effect; therefore, the rate of degradation decreased. As the solution concentration increased, the viscosity increased and caused a reduction in the cavitation efficiency, and so the rate of degradation decreased. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 445–451, 2004 |
