Bio-based phthalonitrile compounds: Synthesis, curing behavior, thermomechanical and thermal properties

Two bio-based phthalonitrile (PN) monomers, eugenol-based phthalonitrile (EPN) and guaiacol-based phthalonitrile (GPN), were successfully synthesized by the reaction of 4-nitrophthalonitrile with eugenol and guaiacol derived from clove and lignin, respectively, in the presence of potassium carbonate via nucleophilic substitution reaction. Their chemical structures were confirmed by the Fourier transform infrared spectra (FTIR), hydrogen and carbon nuclear magnetic resonances (H-1 and C-13 NMR), and elemental analysis. The curing behavior of the blends of the prepared PN monomers with 10 wt% of 4-(4-aminophenoxy)-phthalonitrile (4-APN) as curing agent was evaluated by FTIR and differential scanning calorimetry (DSC), while rheometer was used to analyze the processability of the blends. Moreover, the thermomechanical and thermal properties of the polymers were studied by dynamic mechanical analyzer (DMA) and thermogravimetric analysis (TGA). The results confirmed that the bio-based PN monomers and its blends show low melting temperatures, wide processing windows (> 186 degrees C), and low melt viscosity (< 0.03 Pa.s). The cured bio-based PN resins exhibited higher glass transition temperature and better thermal stability and toughness than those of typical bisphenol A-based phthalonitrile polymer. Meanwhile, the phthalodinitrile resins form a homogeneous, void-free network structure, which also confirm the excellent thermal and mechanical properties of the polymers.