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In this study, we propose an efficient method for preparation of large scale, monodisperse poly(methyl methacrylate-co-butyl acrylate) latexes by application of the low power ultrasound irradiation. The effect of polymerization temperature and initiator concentration on the polymerization nature, particle size, and particle size distribution were investigated. Results indicated that the ultrasound pulses in the first minutes of polymerization increase instant free radical to monomer ratio as well mixing efficiency which led to higher monomer conversion, improved polymerization rate (especially at first 15 min of the reaction), and remarkable decrease in molecular weight distribution. Transmittance electron microscopy (TEM) and dynamic light scattering (DLS) revealed that the particle size and particle size distribution were significantly affected, particle size decreased, and more uniform particles were obtained. Dynamic mechanical thermal analysis also showed that the initiator concentration affected glass transition temperature ([T.sub.g]) of the final copolymers and in the case of ultrasound-assisted emulsion polymerization [T.sub.g] was in a very good agreement with theoretical predictions for copolymerization. POLYM. ENG. SCI., 56:214-221, 2016. [C] 2015 Society of Plastics Engineers, INTRODUCTION Emulsion polymerization is a scientifically, technologically, and commercially important polymerization method. High molecular weight polymers can be produced at fast polymerization rates. The continuous water phase is an excellent [...]