New comblike polymers such as a homopoloymer (poly-4) of 3,5-bis[poly(ethylene glycol) methyl ether (350, n =7.2)]styrene (4) and an alternating copolymer (poly-4/TCNQ) of 4 with 7,7,8,8-tetracyanoquinodimethane (TCNQ) were prepared as a plasticizer for the poly(ethylene oxide) (PEO)-LiN(CF3SO2)2 electrolyte, and the ionic conductivities, thermal property, electrochemical and thermal stabilities, and mechanical property for the comblike-based polymer electrolytes, composed of the comblike polymers, poly(ethylene oxide), and LiN(CF3SO2)2, were investigated. The polymer electrolytes containing an alternating copolymer poly-4/TCNQ showed the higher ionic conductivity, better thermal stability, and better mechanical stability than that containing a homopolymer poly-4, due to the presence of an aromatic ring and a polar cyano group of the TCNQ unit.