The aim of this study was to synthesize graft copolymers of poly(methacrylic acid)-g-poly(epsilon-caprolactone) by a two-step process. In a first part, a macromonomer of 2-hydroxyethylmethacrylate-poly (epsilon-caprolactone) (HEMA-PCL) was synthesized by coordinated anionic Ring Opening Polymerization (ROP). Then graft copolymers were obtained via Reversible Addition Fragmentation chain Transfer (RAFT) copolymerization of HEMA-PCL macromonomer and methacrylic acid (MAA). This two-step synthesis is a really interesting way to adjust and control parameters such as graft density, polymerization degree, copolymer composition, graft length, in order to adapt the final graft copolymers to their future applications. The efficiency of such copolymers in dispersing calcium carbonate into an unsaturated polyester resin has been point out by viscosity measurements. (C) 2011 Elsevier Ltd. All rights reserved.