||In this study, a series of well-defined polyethylene oxide (PEO)-based triblock copolymers containing poly(acrylonitrile) and poly(acrylonitrile-co-dimethyl acrylamide) were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. Trithiocarbonate functional groups were attached to a commercial polyethylene glycol (Mn=2050) to obtain bifunctional PEO-based macro RAFT agent. A comprehensive study was performed to understand the influence of reaction temperature, solvent, and ratio of monomer, macro chain transfer agent (MCTA) and initiator on the polymerization kinetics, molecular weight, and polydispersity. Well-defined copolymers with targeting molecular weight and low polydispersity index at high conversion were obtained by using ethylene carbonate solvent and an optimized [M]0:[MCTA]0:[I]0 ratio at 90°C. The resultant triblock copolymers are highly thermal and mechanically stable.