Bio-Based Self-Curing Phthalonitrile Resins Derived from Cinnamaldehyde

A class of bio-based bifunctional phthalonitrile (PN) resins composed of cinnamaldehyde derivatives, aminophenol, and end-capped with a PN moiety is detailed. The cinnamic-imine PN (CIPN) resins were synthesized by utilizing environmentally friendly solvents methanol (MeOH) and acetone at ambient temperatures. Characterization of the resins was conducted via proton (1H) and carbon (13C) nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), infrared spectroscopy (IR), mechanical analysis, single crystal X-ray diffraction (XRD), and rheometry. The CIPN resins were self-curing due to the vinylic, imine, and PN moieties present and displayed a range of viscosities from 153–1546 cP at 225 °C. The resulting CIPN polymers were prepared by post-curing up to 380 °C and exhibited excellent thermal stability with Td5% above 510 °C up to an 80% char yield. Moderate brittleness ranging from an initial storage modulus (G′ at 25 °C) of 86–1295 MPa was observed among the CIPN resins. This combination of properties suggests that the bifunctional CIPN resins are excellent materials for high temperature thermosets in composite applications.