Synthesis and thermal properties of high temperature phthalonitrile resins cured with self-catalytic amino-contanining phthalonitrle compounds

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.