The synthesis of fluorinated polyimide/fluorinated polyhybridsiloxane (FPI-FPHSX) block copolymers was achieved through the polycondensation of α,ω-dichlorosilane fluorinated polyimides and α,ω-disilanol fluorinated polyhybridsiloxanes. Three FPI-FPHSX block copolymers with 41, 50, and 76 wt % polyimide were synthesized and characterized by the tuning of the number-average molecular weight of the soft polyhybridsiloxane segments. The influence of the soft-segment length on the behavior of the thermoplastic elastomer material was studied, including the surface tension and thermal properties. The thermomechanical properties of the FPI-FPHSX block copolymers were also examined. © 2005 Wiley Periodicals, Inc.