AbstractIn this study, a series of nonsolvents including ethyl acetate (EAC), acetic acid (HAC), n‐butyl alcohol (NBA), iso‐propyl alcohol (IPA) and ethanol (EA) were selected during the phase inversion process of poly(arylene ether nitrile) (PEN) films. The mechanism of film formation was tightly related with the interactions among polymer, solvent and nonsolvent. In the case of EAC, the aggregated sphere in P‐EAC confirmed the in situ aggregate mechanism of polymer chains during the phase inversion process. As the nonsolvent‐polymer interaction increases from HAC, NBA, IPA to EA, the phase inversion mechanism was gradually changed from the delayed to transient, as verified by the morphology transformation from spongy‐like to finger‐like. Dielectric, mechanical properties of these PEN films are tightly related with the morphological features, while their thermal properties are similar. Among them, P‐EAC show the optimal properties for potential application in the low‐k films, with a dielectric constant, T_d5%, tensile strength of 1.99, 515.84°C, and 36.08 MPa, respectively. This work can provide references for tailoring the structures and properties of PEN films through rational selection of nonsolvent via the phase inversion method.