Dispersion RAFT polymerization of styrene in the alcohol/water mixture mediated with the brush macro-RAFT agent of poly[poly(ethylene oxide) methyl ether vinylphenyl-co-styrene] trithiocarbonate [P(mPEGV-co-St)-TTC] with similar molecular weight but different chemical composition is investigated. Well-controlled RAFT polymerization including an initial slow homogeneous polymerization and a subsequent fast heterogeneous polymerization at almost complete monomer conversion is achieved. The molecular weight of the synthesized block copolymer increases linearly with the monomer conversion, and the polydispersity is relatively narrow (PDI<1.3). The RAFT polymerization kinetics is dependent on the chemical composition in the brush macro-RAFT agents, and those with high content of hydrophobic segment lead to fast RAFT polymerization. The growth of the block copolymer nano-objects during the RAFT polymerization is explored, and various block copolymer nano-objects such as nanospheres, worms, vesicles and large-compound-micelle-like particles are prepared. The parameters such as the chemical composition in the brush macro-RAFT agent, the chain length of the solvatophobic block, the concentration of the feeding monomer and the solvent character affecting the size and morphology of the block copolymer nano-objects are investigated. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3177-3190