ABA triblock copolymers consisting of two terminal blocks (A) of comb-like polymethacrylate with oligo(oxyethylene) side chains (on the average eight oxyethylene units per side chain) and a middle block B of polystyrene were synthesized by anionic polymerization. The ratios A/B were varied, and the respective polymers characterized by 1H and 13C NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The polymers were then solution-cast from tetrahydrofuran solutions of lithium perchlorate, and the homogeneous, solvent-free polymer electrolyte systems tested for their thermal characteristics (DSC) and conductivity. The inclusion of a polystyrene block in the comb-like polymethacrylate electrolyte vastly improves their film-forming and mechanical properties, but also lowers the conductivity. Addition of dimethyltetraethyleneglycol (2,5,8,11,14-pentaoxapentadecane) enhances the ion conduction which can reach values of 10−4 Ω−1 · cm−1 at 70°C, depending on salt and styrene content.