AbstractA new polyesterimide containg CC‐double bonds was prepared by reacting an unsaturated diacid chloride containing a cyclic imido group with ethylene glycol at low temperature. The solubility, thermal, electrical and cross‐linking properties of the polymer were studied. The polymer was found to be thermostable and soluble in highly polar solvents. X‐ray diffraction data revealed that the polymer is crystalline. The unsaturation sites of the polymer chain could be exploited for crosslinking reactions. The swelling behavior of the crosslinked polymer was studied as well as the thermal and electrical properties. The overall thermal stability of the crosslinked polymer was found to be higher than that of the uncrosslinked po