Low-melting maleimide-containing phthalonitrile resins: Synthesis, curing behavior, and thermal performance

Phthalonitrile (PN) resins are highly valued in high-performance applications due to their exceptional thermal stability and mechanical properties. However, traditional PN monomers suffer from high melting points and slow curing rates, often requiring external curing accelerators that can compromise thermal performance. This study focuses on the synthesis and characterization of novel low-melting maleimide-containing PN monomers designed to enhance curing efficiency and thermal properties. Maleimide groups were introduced to improve self-catalytic properties, facilitating a more efficient curing process. The polymerization behavior, thermal stability, adhesive, and mechanical properties of these compounds were thoroughly investigated. Differential Scanning Calorimetry (DSC) and rheological tests showed that incorporating alkyl groups significantly improved flow properties, facilitating easier processing. The difference in the three-dimensional network structures of the cured PN resins was confirmed by Fourier Transform Infrared (FT-IR) spectroscopy. Thermogravimetric Analysis (TGA) demonstrated outstanding thermal stability, with 5 % weight loss temperatures ranging from 387 °C to 418 °C under air and from 420 °C to 471 °C under nitrogen. Dynamic Mechanical Analysis (DMA) confirmed high glass transition temperatures ( Tg ) exceeding 400 °C, indicating superior thermal performance and making these resins suitable for advanced applications in harsh environments. These findings suggest that low-melting maleimide-containing PN systems are promising candidates for high-performance materials in aerospace, electronics, and other demanding fields. • Low-melting maleimide-containing PN monomers were synthesized to improve curing efficiency. • These resins exhibit high thermal stability with glass transition temperatures exceeding 400 °C. • FT-IR confirmed the formation of nitrogen-heterocyclic structures during the curing process. • Maleimide-containing PN resins showed excellent adhesion properties at high temperatures. • Flexural strengths of the composite laminates reached up to 650 MPa, suitable for aerospace applications.