Advanced Design and Fabrication of High‐Strength Phthalonitrile Thermosets With Low Dielectric Constants and Enhanced Toughness via Allyl‐Bismaleimide Modification

ABSTRACT Benzoxazine‐containing phthalonitrile (PN) resins exhibit advantages such as low curing temperature, high thermal resistance, and stable electrical properties. However, the relatively high dielectric constant (3.8 at 1 MHz) limits its applications in the electronics field. In this work, bismaleimide resin (BDM) with low dielectric constant and an allyl‐containing bismhenol A (DBA) monomer as a curing agent were innovatively introduced to copolymerize with the PN resin, aiming to further reduce the curing temperature and dielectric constant. To fully exploit the advantages of BDM, it was pre‐polymerized with DBA to obtain BA resin. The influence of BA resin content on the properties of the copolymerized resin (Poly(PN‐BA)s) was systematically investigated. The results show that the introduction of BA resin improves the curing reactivity of the PN‐BA, with a shortening of the gelation time by nearly 200 s (from 631 s of PN to 434 s of PN‐30BA, a decrease of 31.2%), while maintaining good processability. The Poly(PN‐BA)s retain the excellent high‐temperature resistance of Poly(PN) while effectively improving the dielectric properties, reducing the dielectric constant to 3.29. Furthermore, the glass fiber‐reinforced composites G(PN‐BA)s have good bonding of the resin to the fiber interface, and the bending strength was enhanced from 351 to 554 MPa, which increased by 58%. Therefore, the Poly(PN‐BA)s exhibits promising application prospects and provides an excellent technical solution for PCB resins.