High-performance trifunctional Benzoxazine resin with Cyano groups: Synthesis, thermal stability, and flame retardant properties

Benzoxazine resins with cyano groups, characterized by abundant nitrogen functionalities and excellent properties after curing, play an important role in the field of advanced materials. In this work, a noval high-performance trifunctional benzoxazine monomer (TH-apn) containing cyano groups was successfully synthesized by using green solvents (PEG 200). The chemical structure of TH-apn was verified by proton nuclear magnetic resonance ( 1 H NMR), 13 C nuclear magnetic resonance ( 13 C NMR), and fourier transform infrared (FTIR) spectrum. The curing behavior and curing kinetic of TH-apn were investigated by differential scanning calorimetry (DSC) and the thermal properties of poly (TH-apn) at different post-cure temperatures were characterized by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Flame retardancy was assessed through using the UL-94 standard vertical flame test and the limiting oxygen index (LOI). Results revealed that poly(TH-apn-280) exhibited higher thermal performance (glass transition temperature ( T g ), initial decomposition temperature ( T 5 ), and char yield at 800 °C ( Y c ) of 395 °C, 459 °C, and 74.9 %, respectively), which was attributed to the cross-linking of cyanine to form a more stable structure after curing at high temperatures. Poly(TH-apn-280) demonstrated outstanding flame retardancy, achieving an LOI of 35.9 %. However, its flexural strength was 24.4 % lower than poly(TH-apn-240). TH-apn resin showed great potential for high temperature ablative materials, which resulted in excellent thermal stability and flame retardancy.