Influence of Temperature on the Ultrasonic Degradation of Poly(vinyl acetate) and Poly(vinyl chloride) Sujay Chattopadhyay, Giridhar Madras Department of Chemical Engineering, Indian Institute of Science, Bangalore— 560012, India Received 7 February 2002; accepted 1 October 2002 ABSTRACT: This study investigates the effect of temper- ature on the ultrasonic degradation of polyvinyl acetate and polyvinyl chloride in chlorobenzene. The time evolution of molecular weight distribution was determined using gel permeation chromatography. Continuous distribution kinet- ics was used to obtain the degradation rate coefficients. The rate coefficients decrease with increasing temperature, and this is attributed to the increase of vapor pressure and the decrease of kinematic viscosity. The degradation rate coef- ficient also changes sharply near the glass transition temper- ature, indicating that this factor may play a role in the degradation process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2818 –2822, 2003 Key words: degradation; gel permeation chromatography; glass transition; viscosity; effect of temperature INTRODUCTION Ultrasound has been used in a variety of applications like homo- and copolymerization, 1 emulsification, 2 and organic reactions. 3 One of the main applications of ultrasound has been in the area of polymer degra- dation. The literature has been summarized in the review articles by Basedow 4 and Price. 5 The study of ultrasound initiated degradation is interesting from both practical and academic viewpoints. 6 Ultrasonic depolymerization is mainly caused by the mechanical forces that arise due to the propagation of ultrasonic waves. These forces are directly associated with cavitation, which is the nucleation, growth, and collapse of vapor-filled bubbles in the liquid. 7 Microjets, formed during the collapse of a bubble, transmits the shear force on to the polymer chain. 8 Unlike photo or thermal, the process of chain breakage is nonrandom and happens specifically at nearly the mid point of the chain. An explanation put forth by Thomas 8 is that the polymer molecule gradually changes its shape (in a shear field) from that of a sphere to a cylinder and then this breaks at the midpoint. Several investigations 9,10 have focused on the physics of shear breakage and the factors that influence the cav- itation. Other than the solvent polymer parameters like the Flory–Huggins and the Huggins constant that play a minor role, the main parameters are the vapor pressure and kinematic viscosity of the solution. 11 Unlike thermal degradation, an increase of temperature leads to reduced rate coefficients. Price 5 cites the work of Schmid and Beuttenmuller, who investigated the degradation of ni- trocellulose dissolved in n-butyl acetate and of polysty- rene in toluene at 40 –120°C. The results indicated that the degradation proceeded more slowly and yielded higher limiting molecular weights at higher tempera- tures. Thomas and Alexander 12 investigated ultrasonic degradation of cellulose nitrate in a series of alkyl ace- tates from 0 to 85°C and observed an optimum temper- ature. The reduced degradation observed at both higher and lower temperatures was explained by ineffective cavitation. Malhotra 13 investigated ultrasonic degrada- tion of hydroxypropyl cellulose in water, ethanol, and tetrahydrofuran at various temperatures. It was con- cluded that for cavitation to occur there must be a critical radius that is dependent on the wavelength and inten- sity of sound, density, viscosity, and surface tension of the solvent. Recently, Price 14 investigated the degrada- tion of polystyrene in toluene also reported decreasing rate coefficients with increasing temperature. To our knowledge, we are unaware of any study on the ultrasonic degradation of polyvinyl acetate (PVAc) and polyvinyl chloride (PVC) over an extensive tem- perature range. The objective of this study is to inves- tigate the degradation of these polymers in chloroben- zene. The variation of the rate coefficients with tem- perature is attributed to the change in the kinematic viscosity and vapor pressure. EXPERIMENTAL Ultrasound degradation experiments PVAc (prepared by bulk polymerization) and PVC (Aldrich Chemicals) were used for the experiments. The solvent chlorobenzene (S. D. Fine Chemicals) was Correspondence to: G. Madras (giridhar@chemeng.iisc. ernet.in). Journal of Applied Polymer Science, Vol. 88, 2818 –2822 (2003) © 2003 Wiley Periodicals, Inc.