o-BDB, m-BDB and p-BDB monomers with imperfect crystal structures were synthesized by a nucleophilic substitution reaction.

Resorcinol-based phthalonitrile (R-CN)/nano-aluminum oxide (Al 2 O 3 ) nanocomposites were prepared via a two-step approach. Firstly, Al 2 O 3 was functionalized with nitrile groups on the surface of Al 2 O 3 nanoparticles, which was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy (SEM). The effect of nano-Al 2 O 3 particles on thermomechanical and flexural properties has been evaluated for different weight ratios ranging between 0% and 5%. Compared with pure nano-Al 2 O 3 , nitrile-functionalized Al 2 O 3 (CN-Al 2 O 3 ) particles showed a more significant enhancement effect on the properties of R-CN resin. The storage modulus of nanocomposite with 5 wt% CN-Al 2 O 3 reaches 2679 MPa at 25 C, which is much higher than that of the pure R-CN resin. For 3 wt% CN-Al 2 O 3 -reinforced R-CN composites, it showed an increase of 54.84% in flexural strength and 21.48% in flexural modulus. SEM was employed to explore the fracture surface of composites. Micrographs of fracture surface analysis confirmed that the toughness of R-CN resin can be improved significantly by incorporating CN-Al 2 O 3 nanoparticles.

A series of self-catalytic phthalonitrile compounds with o-, m-, and p- amino groups, namely, 4-(2-aminophenoxy)phthalonitrile (2-NH2-CN), 4-(3-aminophenoxy)phthalonitrile (3-NH2-CN), and 4-(4-aminophenoxy)phthalonitrile (4-NH2-CN), were synthesized via a facile nucleophilic displacement of a nitro-substituent with 4-nitrophthalonitrile. The phthalonitrile resins were prepared by curing 2-NH2-CN, 3-NH2-CN, and 4-NH2-CN with 1,3-bis(3,4-dicyanophenoxy) benzene ( m-BDB). The structures of these compounds were characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and wide-angle X-ray diffraction. Curing behaviors of 2-NH2-CN, 3-NH2-CN, and 4-NH2-CN with m-BDB were recorded by differential scanning calorimetry. The results show that the processabilities of m-BDB with 4-NH2-CN are superior to those with 2-NH2-CN and 3-NH2-CN due to higher self-catalytic efficiency and broader processing windows. Thermal stabilities were evaluated by thermogravimetric analysis, and the polymers with all these self-catalytic compounds exhibit excellent thermal and thermal-oxidative stabilities. Dynamic mechanical analysis reveals that these polymers have high storage modulus and high glass transition temperatures. The polymers of 4-NH2-CN show more outstanding processability, thermal stability, and dynamic mechanical properties than those of 2-NH2-CN and 3-NH2-CN and can be considered as a good candidate as a self-catalytic curing agent for high-temperature phthalonitrile polymers.