A series of novel poly(urethane-PEO-polar siloxane)copolymers and their complexes with LiClO4, were prepared for assessment as polymer electrolytes and characterized by IR, GPC, and DSC, and their ionic conductivity and thermal stability were tested. The incorporation of polar siloxanes into U-PEO greatly increased conductivity. The highest conductivity was 2.6 X 10(-5) S cm(-1) at 25 degrees C. The correlation between T-g, conductivity, and the ratio of siloxane to PEO as well as stability of the polymers are discussed.