Synthesis and Properties of Polycarbosilanes Having 5-Membered Cyclic Carbonate Groups as Solid Polymer Electrolytes

We conducted ring-opening polymerization of silacyclobutane monomers 1-[2-(2,4-dioxa-3-pentanoyl)ethyl]-1-methylsilacyclobutane (SBMC) and 1,1-di[2-(2,4-dioxa-3-pentanoyl)ethyl]silacyclobutane (SBDC) to obtain polySBMC and polySBDC, respectively, and measured their ionic conductivity with addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium trifluoromethanesulfonate (LiOTf). The ionic conductivity of both polySBMC and polySBDC increased with the increase in the amount of LiTFSI added. The ionic conductivity of polySBMC decreased with the increase in the amount of LiTOf, and that of polySBDC decreased after an increase. PolySBMC and polySBDC showed ionic conductivity of 6.1 × 10–5 and 1.5 × 10–4 S/cm at 30 °C, respectively, after the addition of 4 mol equiv of LiTFSI per cyclic carbonate. Differential scanning calorimetry analysis of the polymer revealed that the polymers with a high LiTFSI content formed a crystalline phase around room temperature, but the glass transition temperatures of the amorphous phases were kept low. Infrared analysis suggested the existence of a strong interaction between carbonate carbonyl groups and lithium cations.