Preparation and characteristics of natural rubber/poly(ethylene oxide) salt hybrid mixtures as novel polymer electrolytes

Poly(ethylene oxide) (PEO) of molecular weight 1000 (PEO₁₀₀₀) containing lithium benzenesulfonate (LiBs) (PEO₁₀₀₀/LiBs), PEO derivatives having benzenesulfonate groups on both chain ends (PEO₁₀₀₀–(BSLi)₂), or 1-ethyl-2,3-dimethylimidazolium bromide (ImB), were each blended with natural rubber (NR). The ionic conductivity was measured from AC impedance values. The ionic conductivity of the mixture of NR and PEO₁₀₀₀/LiBs (40 wt%) was about 10⁻⁶ S cm⁻¹ at 50°C; this mixture retained rubbery physical characteristics. At NR content of 10 wt%, the ionic conductivity of the mixture (NR/PEO₁₀₀₀/LiBs) was 2.7×10⁻⁵ Scm⁻¹ at 50°C, approximately 10 times higher than that of the bulk PEO/LiBs mixture. For mixtures of NR and PEO₁₀₀₀–(BSLi)₂, no improvement in ionic conductivity by mixing was found. The ionic conductivity of the mixture of NR and ImB was about 10 times higher than for the bulk of PEO₁₀₀₀–(BSLi)₂ at a NR content of 10 wt%. We propose that the ionic conductivity of the mixture increases when an ion conducting matrix containing simple salt is added. On the other hand, the DSC curve for NR/PEO derivatives showed two T_gs based on the separate components, suggesting phase separation of the PEO derivative in the NR phase.