Solid polymer electrolytes (SPEs) have attracted much attention as ion conducting materials with some important advantages over electrolyte materials with low molecular weight flammable and volatile liquid [1]. As a polymer for SPEs, poly(ethylene oxide) (PEO) is most representative and frequently employed, where Li cation coordinates oxygen atoms in the polymer backbone and Li cation is transported with segmental motion of the polymer chain [2–6]. Although somewhat high Li conductivity has been achieved with PEOs doped with an appropriate Li salt, the drawback of the materials is that the conductivity significantly drops at lower temperatures, especially below glass transition temperature (Tg) of the Li salt-doped PEOs, where the polymer segmental motion is greatly suppressed. To overcome the defect of the PEO-based SPEs, poly[2,6-dimethoxy-N-(4-vinylphenyl)benzamide] poly1 (Chart 1) was prepared by Nishimura and coworkers in 2005 [7], and was proposed as a new SPE material, where not the segmental motion of a polymer chain but C–C bond [C(carbonyl)–C(Ph)] rotation in the side chain