Effects of lithium salt on chitosan-g-PMMA based polymer electrolytes

Abstract A grafted copolymer [chitosan-g-poly(methyl methacrylate) (PMMA)] was prepared via gamma irradiation induced graft polymerisation technique. The degree of grafting (DG) increased with increasing absorption dose. The change of structure in the chitosan backbone upon methyl methacrylate grafting was monitored by Fourier transform infrared spectroscopic analysis. Differential scanning calorimetry was carried out to examine the reduction in crystallinity of chitosan due to the branching effects of PMMA segments on chitosan. Differential scanning calorimetry trace of chitosan-g-PMMA has a glass transition temperature Tg at 110°C. Thermal gravimetric analysis was used to evaluate the thermal stability. Polymer electrolytes based on chitosan-g-PMMA were then prepared by doping lithium triflate into the grafted solution. These grafted polymers containing different amounts of salts were investigated as possible ionic conducting polymers. The ionic conductivity of the electrolytes was determined at various DGs. The conductivity of the electrolytes was found to increase with the increase in DG. The highest ionic conductivity of chitosan-g-PMMA–LiTf was 4·05×10−5 S cm−1 for the film containing 60·0 wt-% LiTf.

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