AbstractPolymerization of methyl methacrylate with Grignard reagents and benzoyl peroxide under ultrasonic irradiation was carried out and the effect of the ultrasonic irradiation on the stereoregularity and the properties of the polymers obtained was studied. No effect of ultrasonic irradiation on the stereoregularity of the polymers was observed, but the yield and the intrinsic viscosity of the polymers were lower than those of polymers produced without ultrasonic irradiation. It is, therefore, assumed that the bonds at a propagating site between an active polymer end and a counterion are fairly strong and are not broken by the externally applied energy corresponding to an ultrasonic wave of 500 keycles/sec., even though carbon–carbon covalent bonds in the main chain are broke
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