Defined diblock and triblock copolymers composed of methyl methacrylate-co-glycidyl methacrylate block and 3-{3,5,7,9,11,13,15-hepta(2-methylpropyl)-pentacyclo[9.5.1.13,9.15,15.17,13]-octasiloxan-1-yl}propyl methacrylate block(s), i.e., P(MMA-co-GMA)-b-PiBuPOSSMA and PiBuPOSSMA-b-P(MMA-co-GMA)-b-PiBuPOSSMA, were synthesized by atom transfer radical polymerization (ATRP). First, monofunctional and bifunctional P(MMA-co-GMA) copolymers were synthesized by ATRP. Subsequently, these copolymers were successfully used as macroinitiators for ATRP of POSS-containing methacrylate monomer. The process showed high initiation efficiency of macroinitiators and led to products with low dispersity. The synthesized block copolymers were characterized by size exclusion chromatography, 1H-NMR spectroscopy and their glass transition temperatures were determined by differential scanning calorimetry. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013