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Dielectric spectroscopy (DS) measurements were performed to probe the segmental dynamics and ion mobility of poly(vinyl chloride‐co‐vinyl acetate‐co‐2‐hydroxypropyl acrylate) terpolymer dopped with different amounts of tetrabutylammonium tetrafluoroborate ([TBA] [BF4]) ionic liquid (IL). Differential scanning calorimetry (DSC) was also employed to trace the change in the glass transition temperature (Tg) at different loads of IL. The DSC measurements revealed a remarkable reduction in the PVVH Tg from 344 to 310 K just by adding 20 wt% of IL. The DS measurements revealed three relaxation processes named α, β1, and β2. The α‐process is related to the segmental motion of PVVH while the β1 and β2 are due to the restricted local dynamics of side chains. The segmental relaxation times (α‐relaxation) speed up with increasing the concentration of IL due to the plasticization effect of IL on polymer chains. The temperature dependence of α‐relaxation follows the Vogel‐Fulcher‐Tammann (VFT) relation with dynamic glass transition between 323 and 294 K in agreement with the DSC measurements. The β1 and β2‐relaxations have an Arrhenius temperature dependence. The temperature dependence of ionic conductivity obeys the VFT behavior indicating the coupling between the segmental motion of PVVH chains and ion transport. Polaronic tunneling is the predominant conduction mechanism in PVVH and its composites. The specific capacitance increases with increasing both the temperature and IL concentration. [ABSTRACT FROM AUTHOR]