Aqueous emulsion polymerizations of styrene were performed in the presence of a macromolecular reversible addition-fragmentation chain transfer (RAFT) agent (macro-RAFT) composed of acrylic acid (AA) and poly(ethylene oxide) methyl ether acrylate (PEOA), end-capped by a reactive dodecyl trithiocarbonate group (P(AA-co-PEOA)-TTC). The influence of the stirring speed or the presence of different amounts of a divalent salt, CaCl2, were investigated in this polymerization-induced self-assembly process, in which spherical and nonspherical nano-objects were formed upon the synthesis of amphiphilic diblock copolymers in situ. It appeared that the addition of CaCl2 led to the controlled formation of different nano-objects such as spheres, fibers or vesicles, whereas an appropriate stirring speed was required for the formation of nanofibers. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3346-3354, 2011