EFFECTS OF COMPOSITION AND SEQUENCE DISTRIBUTION ON IONIC-CONDUCTIVITY IN POLY(ETHYLENE OXIDE-CO-PROPYLENE OXIDE) BASED NETWORK POLYMERS COMPLEXED WITH LITHIUM PERCHLORATE

Effects of composition and sequence distribution on ionic conductivity have been investigated in the network polymer electrolytes based on poly(ethylene oxide-co-propylene oxide) (EO/PO copolymer) and lithium perchlorate (LiClO4). The polymer electrolytes were prepared by cross-linking reaction of EO/PO copolymer triol with 4-methyl-1,3-phenylene diisocyanate, followed by complexation with LiClO4. The introduction of PO units into PEO sequence and the complexation with LiClO4 made the polymer electrolytes completely amorphous. The increase in glass transition temperature (T(g)) of the network polymers with increasing LiClO4 concentration was greatly affected by sequence distribution of the copolymer. The increase in the random copolymer networks was much larger than that in the block copolymer, and the latter increase was approximately equal to that of PEO networks, while the former increase approached that of PPO networks with increasing PO composition. Ionic conductivity of the polymer electrolytes at low LiClO4 concentrations was mainly affected by the EO composition of the copolymers, and the higher was the EO composition, the higher was the ionic conductivity, whereas that at high concentrations was affected not only by the EO composition but also by the difference in T(g) owing to the difference in the sequence distribution. Random and block copolymer electrolytes of EO mole fraction of 0.84 had favorable ionic conductivity of 10(5) S cm1 at 30-degrees-C and 10(7) S cm1 even at -10-degrees-C. Li1 transference number was 0.15 to 0.4, depending on the composition and sequence distribution of the copolymers, concentration of LiClO4, and temperature.