From polymer to polyelectrolyte: Studies of star-branched poly(ethylene oxide) with lithium functional groups

Star-branched poly(ethylene oxide) with PG-PPO core has been synthesized. The branched structure had on average 18 poly(ethylene oxide) arms with average molecular weight of 1680. The chain ends were capped with OH groups which were then substituted with lithium-containing P(O)(OLi)2, COOLi and SO3Li groups. The substitution level ranged from 30% to 95%. Characterization of physical properties was carried out by various methods, including differential scanning calorimetry and impedance spectroscopy. The results show that polymers with functional groups containing lithium are characterized by relatively high ionic conductivity. The highest ionic conductivity, reaching 8 × 10−6 S/cm at 20 °C was obtained for polymer with P(O)(OLi)2 groups, which demonstrates possibility of using these polymers as polyelectrolyte. It has been also found, that the presence of end groups can decrease crystallinity and lower glass transition temperature of polymer. Electrolytes formed by adding LiN(CF3SO2)2 salt to polymers with functional groups containing lithium had higher ionic conductivity and lower glass transition temperature than electrolytes based on polymer without such groups.