Preparation and properties of a novel silicon- and alkynyl-containing phthalonitrile resin with enhanced processability and thermal stability

To expand the application of phthalonitrile resins in high-temperature environments, we designed and synthesized a novel phthalonitrile monomer (SiBEPN) containing both silicon and internal alkynyl groups, along with its silicon-free counterpart (DEBPN). The structural characterizations of both SiBEPN and DEBPN monomers were conducted using ¹H nuclear magnetic resonance (¹H NMR), Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS). SiBEPN demonstrated significantly lower melting point and higher solubility compared to DEBPN. Their curing behaviours were systematically investigated via differential scanning calorimetry (DSC) and FTIR analysis, while the processability was evaluated by rheological tests. Thermal properties were analyzed using thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA), revealing excellent thermal stability for both cured resins. The 5% weight loss temperatures (T_d5) of p-SiBEPN and p-DEBPN with DDS reached 530°C and 569°C in N₂, respectively, with glass transition temperatures (T_g) exceeding 450°C. Furthermore, quartz fiber reinforced SiBEPN (QF/p-SiBEPN) composites exhibited superior mechanical properties compared to QF/p-DEBPN at all tested temperatures. The room-temperature flexural strength and interlaminar shear strength of QF/p-SiBEPN were 338.32 MPa and 24.30 MPa, respectively. Notably, these composites maintained 62.1% and 57.3% of their initial strengths at 500°C, demonstrating outstanding high-temperature performance.