The role of free radicals in the degradation of high polymers by ultrasonics and by high‐speed stirring

High molecular weight polymethacrylic acid in aqueous solution is rapidly broken down by ultrasonics (250 kc.). The rate of degradation varies as the shape of the molecule in solution is altered and is greatest when most asymmetric. It is concluded that cavitation is essential for the breakdown of the polymer molecules and that the reaction proceeds by two mechanisms. The major part of the reaction is due to mechanical forces produced on the collapse of the cavity but chemical degradation by HO 2 radicals also occurs. Polymerization experiments confirm that free radicals are formed during cavitation. The quantity of H 2 O 2 formed by ultrasonics is much greater than the number of free radicals produced and a separate mechanism for its formation must be postulated. High‐speed propellers, e.g. , in a “Waring Blendor,” bring about cavitation and degradation of polymethacrylic acid.