Well-defined poly(dimethylsiloxane)-block-poly(methyl methacrylate)-block-poly(2,2,3,3,4,4,4-heptafluorobutyl methacrylate) (PDMS-b-PMMA-b-PHFBMA) triblock copolymers were synthesized via atom transfer radical polymerization (ATRP). Surface microphase separation in the PDMS-b-PMMA-b-PHFBMA triblock copolymer films was investigated. The microstructure of the block copolymers was investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Surface composition was studied by X-ray photoelectron spectroscopy (XPS). The chemical composition at the surface was determined by the surface microphase separation in the PDMS-b-PMMA-b-PHFBMA triblock copolymer films. The increase of the PHFBMA content could strengthen the microphase separation behavior in the PDMS-b-PMMA-b-PHFBMA triblock copolymer films and reduce their surface tension. Comparison between the PDMS-b-PMMA-b-PHFBMA triblock copolymers and the PDMS-b-PHFBMA diblock copolymers showed that the introduction of the PMMA segments promote the fluorine segregation onto the surface and decrease the fluorine content in the copolymers with low surface energy. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 156-164, 2011