The grafting reaction of epoxidized natural rubber with carboxyl ionic liquids and the ionic conductivity of solid electrolyte composites

A novel hybrid material was prepared via a grafting reaction of 50% epoxidized natural rubber (ENR 50) with 1-carboxymethyl-3-methylimidazoliumbis(trifluoromethylsulfonate)imine ([(HOOC)C1C1Im][NTf2]). The grafting reaction and cross-linked structure of the hybrid material were investigated using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, differential scanning calorimetry (DSC) and the equilibrium swelling method. The analysis results indicated that the carboxyl group of [(HOOC)C1C1Im][NTf2] can react with the epoxy group of ENR 50 to generate an ENR 50–[(HOOC)C1C1Im][NTf2] graft polymer under conditions of 40 °C for 24 h. Furthermore, the grafting of ENR 50 formed ionic clusters and led to ionic crosslinking. In addition, ENR 50/[(HOOC)C1C1Im][NTf2]/LiTFSI electrolyte composites were prepared through introducing bis(trifluoromethanesulfon)imide lithium salt (LiTFSI) into the ENR 50/[(HOOC)C1C1Im][NTf2] hybrid system and the ionic conductivity of these electrolyte composites were studied. The results showed that the electrolyte composites have high ionic conductivity and reached a maximum ionic conductivity of 3.01 × 10−4 S cm−1 (23 °C) in the experimental range.