Preparation of Self‐Curing, High Temperature Phthalonitrile Resins via Mono‐ and Dihydroxybenzaldehydes

This study examines the synthetic and curing processes for bi‐ and trifunctional end‐capped phthalonitrile (PN) Schiff base resins derived from phenolic aldehydes. Characterization of the resins was conducted via proton ( 1 H) and carbon ( 13 C) nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), mechanical analysis (torsion), rheometry, in‐source fast pyrolysis mass spectrometry (FP‐MS), and solid‐state NMR. The processing window for each resin was determined using DSC, with both bifunctional resins exhibiting relatively low melting points (57°C and 62°C) and large processing windows greater than 200°C. Each resin was self‐curing due to the imine and PN curing groups present and displayed a range of viscosities from 546 to 10,800 cP at 175°C. The resins were degassed and cured into their respective polymers by post‐curing up to 380°C. The resulting polymers all exhibited excellent thermal stability with a T d5% above 500°C in both an inert (N 2 ) and air atmosphere as well as a 73%–75% char yield under N 2 . Excellent toughness was observed for three of the resins with an initial storage modulus ( G' at 50°C) above 1530 MPa and moderate modulus retention. This combination of properties suggests the multi‐functional resins are excellent materials for high‐temperature and mechanical applications.