In this study, a block copolymer of methyl methacrylate (MMA) and styrene (St) synthesized by combined ultrasonic irradiation and reverse atom transfer radical polymerization (RATRP) processes was used. PMMA-b-PSt was partially hydrolyzed and converted to a lithium salt, PMMA-b-PSt-Li, before the electrotheological (ER) measurements carried out. Average particle diameter of PMMA-b-PSt-Li polymeric salt was determined by dynamic light scattering (DLS) as 22 mu m. Suspensions of PMMA-b-PSt-Li polymeric salts were prepared in silicone oil. ER properties of PMMA-b-PSt-Li/silicone oil suspensions were studied as a function of electric field strength, dispersed phase concentration, shear rate, shear stress, temperature, frequency, and polar promoter. Further dielectric properties of PMMA-b-PSt-Li ionomer were also investigated. (c) 2005 Elsevier Inc. All rights reserved.