A well-defined (PEO-PS)2-PLA miktoarm terpolymer (1) was synthesized by stepwise click reactions of individually prepared poly(ethylene oxide) (PEO), polystyrene (PS, polymerized by atom transfer radical polymerization), and polylactide (PLA, polymerized by ring-opening polymerization) blocks. As characterized by differential scanning calorimetry and small-angle X-ray scattering techniques, the terpolymer self-assembled into a hexagonal columnar structure consisting of PLA/PEO cylindrical cores surrounded by PS chains. In contrast, the ion-doped sample (1-Li+) with lithium concentration per ethylene oxide = 0.2 exhibited a three-phase lamellar structure, which was attributed to the microphase separation between PEO and PLA blocks and to the conformational stabilization of the longest PLA chain. The two-phase columnar morphology before the ion doping was used to prepare a nanoporous material. PLA chains in the cylindrical core region were hydrolyzed by sodium hydroxide, producing nanopores with a pore diameter of about 14 nm. The resulted nanoporous material sank to the bottom in water, because of water-compatible PEO chains on the walls. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013