AbstractAlkali‐metal salts of (ω‐carboxy)oligo(oxyethylene) methacrylate (CME12M, M = Li or Cs) have been synthesized and polymerized to prepare solid polymer electrolytes. These types of solid polymer electgrolytes provide a homogeneous phase, since these polymers have a flexible main chain, an oligo(oxyethylene) side chain for ion conduction, and a carrier ion source in one repeating unit. The AC conductivity of P(CME12Li) homopolymer is 8.9 × 10−9S cm−1at 30°C, while that of P(CME12Cs) is 3.3 × 10−6S cm−1at 30°C, which is the highest value among single ion conductors, have been reported as polyelectrolyte “homopolymer” without any additives. High ionic conduction of P(CME12Cs) is due to low glass transition temperature (Tg= −54°C) and weaker ion–ion and ion–dipole interac