Synthesis And Properties Of Bio-based Phthalonitriles

Eugenol-based phthalonitrile monomer（EPN）,guaiacol-based phthalonitrile monomer（GPN）,and cardanol-based phthalonitrile monomer（CPN）were successfully prepared by the reaction of eugenol,guaiacol,and cardanol with 4-nitrophthalonitrile,respectively,in the presence of potassium carbonate via nucleophilic substitution reaction.The chemical structures of the synthesized EPN,GPN,and CPN were confirmed by the Fourier transform infrared spectra（FTIR）,hydrogen nuclear magnetic resonance（¹H NMR）,and carbon nuclear magnetic resonance(¹³C NMR)tests.The curing behavior,polymerization mechanism,and processability of the bio-based PN monomers were evaluated by FTIR,differential scanning calorimetry（DSC）,and a rheological analysis.Dynamic mechanical measurements（DMA）,thermogravimetric analysis（TGA）,universal tensile testing machine,and scanning electron microscope analysis（SEM）were used to analyze the thermal properties,flexural properties,and fracture morphology,theγ-ray irradiation resistance of bio-based phthalonitrile resins was also discussed with⁶⁰Co as the radiation source.In addition,copolymers of bio-based phthalonitriles and phenol-aniline-based monofunctional benzoxazine（P-a）and bisphenol A-aniline-based benzoxazine（BA-a）with multiple weight ratios were prepared.The polymerization behavior,thermal properties,mechanical properties,and fracture morphology of the copolymers were studied.The bio-based phthalonitrile monomers all have low melting temperatures（T_m）and wide processing windows,and as the length of the flexible chains in the molecular structure increases,the T_m of the phthalonitrile monomers decreases,the T_m of the EPN and GPN were102 and 115 ^oC,respectively,and the CPN was oily liquid at room temperature due to the long alkyl side chains in the molecular structure,and the processing windows of EPN,GPN and CPN were observed as 186,195,and 241 ^oC,respectively.The Poly（EPN）and Poly（GPN）exhibited excellent thermal properties,the glass transition temperature（T_g）more than 390 ^oC,the char yields（Y_c）more than 74.8%.The Poly（CPN）has low thermal properties due to its long alkyl chain,but it has excellent toughness.Meanwhile,the chemical structures and thermal properties of the three bio-based phthalonitrile resins remain unchanged afterγ-ray irradiation,which indicaties that there bio-based phthalonitrile resins all have excellent resistance property toγ-ray irradiation.The three bio-based phthalodinitriles were used to modify the benzoxazine resins.The products of benzoxazines ring-opening can promote the cross-linking reaction of phthalonitriles,thus the phthalonitriles can be cured without adding other catalysts.Meanwhile,the introduction of bio-based phthalodinitriles increased the thermal properties and toughness of polybenzoxazine resins.Among them,the overall performance of Poly（BA-a/EPN）-6:4 was significantly higher than other systems,the T_g、T₅ and Y_c were287°C,391°C,and 69.7%,respectively,which were increased by 45.7%,15%and 48.9%respectively than those of pure Poly（BA-a）resins.Meantime,the cardanol-based phthalonitrile greatly improves the toughness of polybenzoxazines,thus which can be used as toughening modifier of benzoxazines.