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Vanillin was used as sustainable source for phthalonitrile monomer synthesis, and allyl/propargyl ether moieties were introduced to improve the processability at the minimal cost of thermal properties. The synthesis route was optimized to minimize side-reactions and simplify post-processing, and the monomers were obtained in high purity and good yields. The curing behavior, mechanism, and processability of the monomers were studied, and the thermal properties of cured polymers were evaluated. Of the two monomers, the allyl ether-containing one exhibited a wide processing window of 185 °C, and was mainly cured into phthalocyanine and linear aliphatic structures through self-catalytic curing process. Also, the glass transition temperature was higher than 500 °C. In contrast, the propargyl ether-containing monomer could only be partially cured, and heat resistance was found to be compromised. Compared with traditional petroleum-based phthalonitrile resins, the bio-based monomers could be cured without the addition of catalysts, and improvement in processability was achieved at no cost of thermal performances.

Soluble hyperbranched poly(arylene ether nitrile)s end-capped by either hydroxyl (HBPAEN-OHs) or phthalonitrile groups (HBPAEN-PNs) were synthesized via nucleophilic substitution reactions, where activated carbon supported calcium oxide was used as the catalyst to avoid crosslinking at high conversion. In order to evaluate their potential application in phthalonitrile resins, these hyperbranched polymers were blended with 1,3-bis(3,4-dicyanophenoxy)benzene and 4-(4-aminophenoxy)phthalonitrile, then cured into polymers. Curing mechanisms of different prepolymers were proposed and compared, and processability, thermal and mechanical properties were characterized. The introduction of HBPAEN-OHs was found to postpone the curing, while thermal and mechanical properties were compromised. On the contrary, the usage of HBPAEN-PNs was beneficial to both processability and thermal properties. More importantly, the impact strength for polymers containing HBPAEN-PN could be as high as 12.92 kJ m−2, indicating such resin could be potentially applied as high temperature structural composite matrices. In addition, the toughening mechanism was proposed and discussed.

Low melting phthalonitrile monomers containing allyl and/or methoxyl groups were designed, synthesized and characterized. In order to evaluate their potential application in phthalonitrile resins, these monomers were blended with 1,3-bis(3,4-dicyanophenoxy)benzene and 4-(4-aminophenoxy)phthalonitrile, then cured into polymers. Curing mechanisms of different prepolymers were proposed and compared, and processability, thermal and mechanical properties were characterized. The introduction of methoxyl units was found to postpone the curing, and thermal properties were slightly compromised. On the contrary, the usage of allyl was beneficial to both processability and thermal properties. More importantly, the impact strength for allyl-containing polymers could be as high as 13.63 kJ m−2, indicating such resin could be applied as high temperature structural composite matrices.