AbstractPolyarylene ether nitrile (PEN) based on biphenol exhibits a high glass transition temperature of 216°C, a high tensile strength of 110 MPa, and low elongation at break of approximately 4%. A series of PEN random copolymers with improved elongation at break were synthesized using various bisphenol compounds and 2,6‐dichlorobenzonitrile (DCBN). The resulting PEN random copolymers exhibited a high glass transition temperature and thermal stability up to 513°C in a nitrogen atmosphere. PEN copolymers were amorphous and could easily be cast into transparent films with a tensile strength of 97.93–117.88 MPa and tensile modulus of 2187.98–2558.44 MPa. Most importantly, elongation at break of these PEN copolymers was higher than 13%. PEN copolymer films had a dielectric constant of 3.77–3.89 at 1 kHz and extremely low dielectric loss (<0.02). At the same time, the breakdown strength of PEN was in the range of 137.92–198.19 kV/mm and energy storage density was in the range of 0.32–0.68 J/cm3. Excellent mechanical, thermal, and dielectric properties of PEN make it possible to use them as high‐temperature resistant dielectrics to act on high‐temperature resistant insulated cables.