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Bifunctional phthalonitrile‐benzoxazine (PNBZ) usually suffers from slow‐curing characteristics. Recently, we unexpectedly observed a waste liquid containing PNBZ solution and excess ethylenediamine (EDA) had turned into a gel at room temperature. Since the report on the PNBZ gelling phenomenon below 150°C was rare, this accidental finding manifested the possible formation of PNBZ gel at low temperatures. By varying the EDA molar ratio, PNBZ gels with different microstructures were successfully realized at the low temperature of 50°C. Through the differential scanning calorimetry, thermogravimetric analyse (TGA), and Fourier transform infrared technique, the driving force behind the gel formation was found to be the low‐temperature copolymerization between the amino group of EDA and the BZ ring of PNBZ, resulting in the amine‐containing intermediate. PNBZ gel was thermally unstable, but was mechanically robust. The current method was also universal to realize polymer or composite gels for a class of slow‐curing PNBZ resin (i.e., allyl‐containing PNBZ gel and its carbon nanotube‐filled composite gel). This study not only expands our understanding of the low‐temperature polymerization behavior of PNBZ but also provides a versatile strategy for low‐temperature preparation of PNBZ‐based gels. Making the most of current approach, it is believed that multifunctional PNBZ‐based gels will be developed for various applications. [ABSTRACT FROM AUTHOR]

In 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, Td5%, 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. [ABSTRACT FROM AUTHOR]