Enhancing the heat resistance, dielectric properties, and flame retardancy of self-curing silicon-based phthalonitrile/quartz composites for a rapid hot-melt prepreg process

The robust operation of electromagnetic waves in communication systems with extreme temperatures relies on high-temperature resistant wave-transparent composites, with organic resin matrix being a pivotal constituent. Enhancing the heat resistance of resins while maintaining excellent processability poses a significant challenge. Herein, a novel “rigid-in-flexible” self-curing silicon-based   silicon-based   phthalonitrile monomer containing phenylacetylene backbone (Si-ALK-PN) was designed. The silazane component disrupts the crystallinity in Si-ALK-PN, resulting in a characteristic of low viscosity (0.3 Pa·s) and extended processing window (>3h). After curing at 450 °C, the resin, namely Si-ALK-PN-450 °C, demonstrated exceptional thermal stability ( T 5%  = 631 °C) and thermo-oxidative stability ( T 5%  = 560 °C). Their quartz fiber-infused composites (Si-ALK-PNs/QF) were manufactured through a straightforward melt processing approach. Upon post-curing at 450 °C, Si-ALK-PN-450 °C/QF exhibited elevated glass transition temperature, flexural strength, and consistent dielectric properties across a wide temperature ranging from 25 °C to 600 °C. Especially, it exhibited excellent flame retardancy as well, stemming from release of eco-friendlyeco-friendly inert gases (NH 3 ) and the high thermal stability of N-enriched all-aromatic PN resin. The design concept of “rigid-in-flexible”, along with the multi-functional group co-curing strategy, offers a promising solution for addressing the trade-off between processing and heat resistance in resins, extending beyond PN resins.