Investigation of Termination During Ultrasonic Depolymerization Ali Ozhan Akyuz, Ahmet Giz, Huceste Catalgil-Giz * Summary: Ultrasound applications provide additional ways in polymerization and copolymerization synthesis. Ultrasonic depolymerization has wide applications in industry and is also used in copolymer synthesis. Another application of depolymer- ization is investigating the termination mechanism and finding the combination/ disproportionation ratio for various monomer-polymer systems. In this work ultra- sonic depolymerization of polyvinyl pyrrolidone and polyacrylamide were investi- gated. Sonications were monitored continuously by the ACOMP (Automatic continuous monitoring of polymerization) system, which provides viscosity, light scattering, ultraviolet and refractive index measurements continuously. Depolymer- izations were performed in the absence and presence of a radical scavenger and disproportionation/combination ratios were discussed for each system. Keywords: chain scission; combination; disproportionation; termination; ultrasound Introduction Low frequency and high intensity ultra- sound is called power ultrasound and has wide applications in biology, chemistry and food industry. Dispersion of solids, homo- genization of emulsions, filtration, crystal- lization and degassing are some of its well known industrial applications. [1–3] Polymer degradation with ultrasound is finding new areas of application. Application of ultra- sound to a polymer solution decreases the molecular weight by breaking the polymer backbone without causing any changes in the chemical nature of the polymer. In high intensity ultrasound there is cavitations; that is, large negative pressure in the rarefaction phase breaks the surface ten- sion and forms microscopic bubbles. Bub- bles grow during rarefaction. The cavitation bubbles implode during the compression phase. Implosions lead to extreme tem- perature and pressures, shock waves and turbulence. In some cases light emission from implosion sites, known as sonolumi- nescence occurs. [4] It is probably this turbulence that breaks the backbones of macromolecules. Depolymerization depends on fre- quency, intensity, solvent, temperature and nature of gas in the solution and applied pressure. [5] Long chains in the polymer solution are affected, however chains shorter than a certain length are immune to scission, thus heterogeneity decreases. These properties of ultrasonic degradation are similar to degradation by shear flow. [6] Ultrasonic degradation is a controlled process and scission occurs predominantly around the middle point. Sonication can be used to control the chain length and polydispersity, which is very important in terms of polymer properties. It is a physical and nonrandom process which also provides additional ways in polymer synthesis, after polymerization. [7–9] Two macroradicals are formed as a result of one scission. Resulting macro radicals can be used further in copolymer synthesis or in block copolymer formation. Macromol. Symp. 2009, 275-276, 112–119 DOI: 10.1002/masy.200950113 112 Istanbul Technical University, Faculty of Sciences and Letters, Maslak, 34469, Istanbul, Tu ¨ rkiye E-mail: catalgil@itu.edu.tr Copyright ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim