High-temperature wave-transparent and intrinsically flame-retardant phthalonitrile/quartz composite based on a straightforward hot-melt prepreg process

Wave-transparent composite materials are becoming increasingly critical for advancing robust human-machine interaction systems. A pivotal component of these systems is an organic resin matrix, which is currently the focus of intensive research. Herein, to develop a phthalonitrile resin capable of withstanding temperatures exceeding 500 °C, two types of Si/P-containing alkynyl curing agents (Si-ALK and P-ALK) were synthesized and integrated with sulfur-enriched phthalonitrile monomers (SSS-PN) to fabricate an organic-inorganic hybrid phthalonitrile(PN)resin. The resulting hybrid resin demonstrated exceptional thermal stability (594 °C for 10% Si-PN-450 °C; 626 °C for 50% P-PN-450 °C) and thermal oxygen stability (569 °C for 10% Si-PN-450 °C; 594 °C for 30% P-PN-450 °C). The Si-ALK/P-ALK and SSS-PN blends maintained stable low-viscosity properties for an extended period of up to 180 min, which is advantageous for the facile production of quartz fiber-infused composites (Si-PN/QF and P-PN/QF) through a straightforward and eco-friendly melt processing approach. The cured PN composite (30% Si-PN-450 °C/QF vs. 10% P-PN-450 °C/QF) exhibited significantly improved glass transition temperatures (506 °C vs. 553 °C), acceptable flexural strength (268 MPa vs. 275 MPa), and excellent flame retardancy (less than 8.0% weight loss exposed at 1300 °C for 200 s). Additionally, the composites demonstrated commendable dielectric properties, with a dielectric constant (Dk) of approximately 4.0 and a dissipation factor (Df) below 0.01 from 25 °C to 600 °C. Collectively, the obtained composites exhibited a synergistic combination of thermal, fire-resistant, and dielectric properties, positioning them as leading candidates for the next generation of wave-transparent materials.