Polymers are prepared by various methods. The method of preparation plays an important role in deciding many of the physical properties of polymers. In this work Poly (Methyl Acrylate), PMA, is synthesized by free radical addition polymerization in the presence a monomer, an initiator under the influence of ultrasound. Methyl Acrylate (E-Merck, India) of proper strength is mixed with aqueous sodium peroxodisulphate solution of known strength and the time of passage of ultrasound is varied in steps of 30 minutes and 10 samples of solid PMA are obtained for 10 different periods of passage of ultrasound. Solid PMA samples are purified and air-dried under clean environment. TGA, DTA measurements are done on all the 10 PMA samples. The thermal stability of PMA with the change in the time of passage of ultrasound is discussed quantitatively. The thermal stability of PMA, synthesized sonochemically shows better results over the thermal method of synthesis. However in this paper we report the measurements made on PMA samples synthesized at 30 and 300 minutes sonication periods respectively.