High molecular weight polyether comb polymers, poly[ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether] P(EO/MEEGE), have been used as matrixes of polymer electrolytes. The high molecular weight (>10(6)) polymers give self-standing and elastic polymer electrolyte films without chemically cross-linked structures at room temperature, when complexed with electrolyte salts. With increasing the composition of MEEGE in the copolymers, the degree of crystallinity of the polymer electrolytes decreases, and the ionic conductivity appreciably increases. The increase in the conductivity cannot be explained only by the crystallinity decrease, the increase in the number of highly mobile ether side chains with the increase in MEEGE composition contributes to achieving the high conductivity. The fast ion transport would be realized in cooperation with the fast side chain motion. The polymer electrolytes complexed with lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) exhibit higher conductivity than those complexed with a conventional salt, lithium perchlorate. The polymer electrolytes, P(EO/MEEGE) containing 9 mol% of MEEGE complexed with LiTFSI, exhibit high ionic conductivities of 10(-4) S cm(-1) at 30 degrees C and 10(-3) S cm(-1) at 80 degrees C. An electrochemically stable potential window, established by solid state cyclic voltammetry using microelectrodes, is at least 4V from the Li/Li+ potential.