The Block copolymer polystyrene-b-poly(acrylic acid)-bpolystyrene (PSt-b-PAA-b-PSt) was synthesized via reversible addition-fragmentation chain transfer polymerization by using styrene as the first monomer.The architectures of the macro-chain transfer agent PSt-CTA and the block copolymers were confirmed by FTIR and 1H-NMR.GPC analysis was used to estimate the molecular weight and the molecular weight distribution of the copolymers

the numeraverage molecular weight of macro-chain transfer agent PSt-CTA was 8320

and the molecular weight distribution was 1.05.The numer-average moleccular weight of three block copolymers was 13050

11130 and 9760

respectively

and the corresponding molecular weight distribution was 1.356

1.430

1.365.The block copolymers with different molecular weights were self-assembled by co-solvent method in an ionic liquid

1-butyl-3-methylimidazolium hexafluorophosphate (［BMIM］［PF6］).The nanostructures of the PSt-b-PAA-b-PSt micelles formed in the ionic liquid were observed by TEM (transmission electron microscopy) and DLS(dynamic light scattering).The self-assembled morphologies of the copolymers are strongly dependent on the length of PAA block chains when the chain length of PSt is fixed.With the decrease of molecular weight of PAA in block copolymers

the resulting aggregates are spheres with diameter of about 50 nm.With further decrease of PAA molecular weight in copolymers

the sphere morphology is turned to core-shell sphere micelles with diameters not more than 100 nm.Compared with the aqueous solutions of the same copolymers

［BMIM］［PF6］ solutions exhibit some distinct features

such as temperatureindependent micellar morphologies between 25℃ and 100℃.