Solid and gel electrolytes based on comblike poly(propylene oxide) (PPO) have been prepared and studied. The polymer consisted of a polyethylene backbone densely grafted with PPO side chains terminated by hexadecanoyl chain ends. Analysis by impedance spectroscopy of the solid polymer electrolytes containing lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) salt showed ion conductivities of 10(-5.5) S cm(-1) at 20 degreesC. The ion conductivity of polymer gel electrolytes containing 1 M LiTFSI in gamma -butyrolactone (gamma -BL) reached 10(-3.0) S cm(-1) at 20 degreesC with 50 wt% of electrolyte solution added. Thermal analysis showed that the comblike PPO aggregated through microphase separation of the hexadecanoyl units in both the solid and the gel electrolytes. This microphase had multiple melting points in the temperature interval between -45 and 40 degreesC. Furthermore, the crystallisation of gamma -BL was greatly suppressed in gel electrolytes. A study of the gel electrolytes by FT-IR spectroscopy implied that the lithium ions were preferentially coordinated by the PPO grafts, and not by gamma -BL.