Immobilization of Ionic Liquids onto the Poly(vinylidene fluoride) by Electron Beam Irradiation

An unsaturated room-temperature ionic liquid (IL), 1-vinyl-3-butylimidazolium chloride [VBIM][Cl], has been grafted onto poly(vinylidene fluoride) (PVDF) by electron beam irradiation at room temperature. The structure and physical properties of IL grafted PVDF (PVDF-g-IL) were investigated. Both the extraction experiments and H-1 NMR results indicated the successful grafting of IL onto PVDF molecular chains. It was calculated that IL grafting yield was approximately 3.9 per 100 repeating units of PVDF, suggesting very short IL grafting sequences. The melting temperatures (T-m) of the PVDF-g-IL films decreased with absorbed dose, suggesting the occurrence of crystal defects of PVDF caused by the irradiation. However, the morphologies, crystal forms and crystal long periods (L) of PVDF-g-IL films were not significantly influenced by the irradiation. Moreover, the effects of IL grafting and absorbed dose on physical properties of PVDF-g-IL films were investigated. It was found that the irradiation could immobilize IL molecules onto PVDF chains and thus suppressed their migration in electric filed. Therefore, the grafted samples showed lower dielectric loss, electrical conductivity as well as dielectric permittivity compared with the unirradiated blends. Moreover, the elongation at break of the grafted PVDF decreased with the applied irradiation dose, but the Young's modulus increased. The as-prepared PVDF-g-IL composites exhibited large dielectric permittivity, low dielectric loss and, in particular, excellent toughness, which is promising for use in dielectric capacitor applications.