A novel ABC triblock copolymer with a rigid-rod block was synthesized by atom transfer radical polymerization (ATRP). First, a poly(ethylene oxide) (PEO)-Br macro-initiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of a poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymer by ATRP. A poly(ethylene oxide)-block-poly(methyl methacrylate)-block-poly {2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PEO-b-PMMA-b-PMPCS) triblock copolymer was then synthesized by ATRP using PEO-b-PMMA as a macroinitiator.