Utilization of carbon dioxide for polymer electrolytes [II]: Synthesis of alternating copolymers with glycidyl ethers as novel ion-conductive polymers

For creation of a novel candidate for the polymer electrolytes without ethylene oxide units in the main chain, we considered polycarbonates obtained from the copolymerization of CO2 with epoxy monomers. In this study, we synthesized six types of polycarbonates possessing glycidyl ethers (phenyl, tert-butyl, n-butyl, ethyl and isopropyl) and ethyl side groups using zinc glutarate, and measured the ionic conductivity of their electrolytes including LiTFSI. The electrolyte possessing ethyl glycidyl side groups had the highest conductivity and the value was 2.9 × 10−7 S/cm at room temperature. DSC measurement showed that some of polycarbonates possessing glycidyl ethers decrease in Tg by the addition of salt, whereas the polycarbonate (P(EP-C)) possessing non-ether side group increase in the Tg. FT-IR measurement revealed that the P(EP-C) electrolyte clearly makes interaction between Li ions and carbonyl groups on the main chain, which is related to the main factor of the increase in Tg.

► Novel ion-conductive CO2/epoxide alternating copolymer electrolytes without ethylene oxide units in the main chain.
► Polycarbonate possessing ethyl glycidyl side groups shows the highest ionic conductivity.
► Addition of LiTFSI decreases glass transition temperature of the polycarbonate.
► Polycarbonate possessing non-ether side groups makes interaction between Li ions and carbonyl groups on the main chain.