Strong and tough phthalonitrile PCB substrates with semi‐interpenetrating polymer network toughened by highly heat‐resistant poly(aryl ether nitrile)

Abstract The toughening of thermosetting resins by thermoplastic resins often comes at the cost of sacrificing heat resistance, which poses a great challenge for preparing the composites with high toughness and high heat resistance. In this work, a phenolphthalein‐type polyarylene ether nitrile (PP‐PEN) was synthesized and toughened bismaleimide‐triazine (BT) resins containing 4‐(4‐amino‐phenoxy) phthalonitrile (4‐APN) to prepare a series of strong and tough poly(BT/PEN) composites with a semi‐interpenetrating polymer network (SIPN). The results showed that the addition of PP‐PEN could significantly reduce the curing temperature of BT resin, and the curing temperature of poly(BT/10PEN) decreased to 233 from 258 °C. Moreover, the Gpoly(BT/PEN) composites reinforced with glass fibers exhibited outstanding heat resistance and mechanical properties. Specifically, the T_g of Gpoly(BT/10PEN) increased to 281 °C from 262 °C, and the thermal expansion coefficient along the z‐axis reached 19 ppm. Impressively, the flexural strength and modulus of Gpoly (BT/10PEN) can reach 581.6 and 40 MPa, respectively, and the impact strength increased from 83.7 kJ/m² of BT resin to 132.0 kJ/m² due to the construction of the SIPN structure, which provides a good idea for preparing high‐strength and high‐toughness printed circuit board substrates with high glass transition temperature. Highlights Poly(BT/PEN)s showed a good processability with the curing temperature of 226 °C. Poly(BT/PEN)s exhibited two glass transition temperatures of 252 and 312 °C, suggesting the SIPN structure. The toughness of poly(BT/PEN)s was greatly improved by adding PP‐PEN, and the impact strength increased to 132.0 MPa from 83.7 MPa. The flexural strength and modulus of poly(BT/10PEN) increased to 581.6 MPa and 40.4 GPa, respectively.