Polyethersulfone (PES) based amphiphilic block copolymer was designed as a hydrophilic additive for the modification of polysulfone (PSf) membranes. The block copolymer with PES as the middle block and poly(ethylene glycol) methyl ether methacrylate (POEM) as side blocks was synthesized via the reversible addition-fragmentation chain transfer (RAFT) polymerization, using a PES-based macro-chain-transfer-agent (macro-CTA). The successful synthesis of the amphiphilic copolymer was confirmed by the nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). Blend membranes were prepared via the non-solvent induced separation method. The differential scanning calorimetry (DSC) spectra of blend membranes displayed single glass transition temperatures (T-g), indicating the miscibility between the PSf and PES main chains. The melting peak at 37.4 degrees C presented the phase separation of POEM from hydrophobic domains in membranes. The great improvements in hydrophilicity, fouling-resistance, and water flux were found when the modifier was introduced. At last, the intact of RAFT agents from the additives were made use of to graft zwitterionic brushes on membrane surface. Crown Copyright (C) 2011 Published by Elsevier B. V. All rights reserved.