A series of well-defined and property-controlled polystyrene (PS)-b-poly(ethylene oxide) (PEO)-b-polystyrene (PS) triblock copolymers were synthesized by atom-transfer radical polymerization, using 2-bromo-propionate-end-group PEO 2000 as macroinitiatators. The structure of triblock copolymers was confirmed by H-1-NMR and GPC. The relationship between some properties and molecular weight of copolymers was studied. It was found that glass-transition temperature (T-g) of copolymers gradually rose and crystallinity of copolymers regularly dropped when molecular weight of copolymers increased. The copolymers showed to be amphiphilic. Stable emulsions could form in water layer of copolymer-toluene-water system and the emulsifying abilities of copolymers slightly decreased when molecular weight of copolymers increased. (c) 2006 Wiley Periodicals, Inc.