Reducing the Melting Point and Curing Temperature of Aromatic Cyano-Based Resins Simultaneously Through a Brønsted Acid-Base Synergistic Strategy

High melting points (M-p) and high curing temperatures are two key processing problems that limit the application of aromatic cyano-based (AC) resins. A Brunsted acid-base synergistic strategy based on an acid-base eutectic and mechanisms for nucleophilic addition and ionization equilibrium are proposed to reduce the M-p and curing temperature of AC resins. Blends of 4,5-dicyanoimidazole (DCI, Brunsted acid) and amine-containing phthalonitriles (4-(4 or 2 or 3)-aminophenoxy) phthalonitrile, APNs, Brunsted bases) were selected as model acid-base systems to study the synergistic behaviors in processing. The results show that the M-p and the peak exothermic temperature (T-rp) of APN-DCI blends can be reduced by more than 31 degrees C and 85 degrees C compared with their intrinsic components, respectively. DSC and XRD show that the decrease in the Mp of the blends is induced by the formation of eutectics. A positive relationship between Delta pKa and the curing reactivity is confirmed by theory and experimental methods. The cured products show outstanding thermal and mechanical properties compared with reported AC resins. This research provides a new convenient route for regulating the curing behavior of AC resins and will significantly promote the development of high-performance AC resins.