Design and Construction of Furan‐Based and Thiophene‐Based Salicyladazine Bisbenzoxazine Resins with High Thermal Stability and Tunable Surface Properties

Abstract

AbstractTwo disubstituted bisbenzoxazine (Bz) monomers are synthesized using furan (Fa) and thiophene (Th) derivatives: bis((3‐(furan‐2‐ylmethyl)‐7‐ol‐3,4‐dihydro‐2H‐benzo[e][1,3] oxazin‐6‐yl)methylene)hydrazine (BAZ‐Fa‐BZ) and bis((3‐(thiophen‐2‐ylmethyl)‐7‐ol‐3,4‐dihydro‐2H‐benzo[e][1,3] oxazin‐6‐yl)methylene)hydrazine (BAZ‐Th‐BZ). These monomers are synthesized via Mannich condensation of salicylaldazine (1,2‐bis(2,4‐dihydroxybenzylidene)hydrazine (BAZ─4OH)) and paraformaldehyde (CH2O)n, with furfurylamine (FacNH2) and thiophene‐2‐methenamine (Th─NH2), respectively. The chemical structures of BAZ‐Fa‐BZ and BAZ‐Th‐BZ are affirmed using Fourier‐transform infrared spectroscopy (FTIR) and NMR, respectively. A thorough investigation of the thermal polymerization process of BAZ‐Fa‐BZ and BAZ‐Th‐BZ is conducted using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and in situ FTIR spectra (ranging from 25 to 250 °C). Poly(BAZ‐Fa‐BZ) exhibits superior thermal properties with a thermal decomposition temperature (Td10) of 402 °C and a char yield of 58 wt% after thermal treatment at 250 °C, along with a lower surface free energy of 28.9 mJ m−2 compared to poly(BAZ‐Th‐BZ) (Td10 = 359 °C, char yield = 48 wt%, and surface free energy = 34.1 mJ m−2). Additionally, poly(BAZ‐Th‐BZ/BAZ‐Fa‐BZ) blend with a ratio of 1/3 after thermal curing at 250 °C demonstrates the highest Td10 of 395 °C and a char yield of 60 wt%. Photoluminescence (PL) measurements conducted in the solid state reveal that BAZ‐Th‐BZ, BAZ‐Fa‐BZ, and their blends emit green light when excited at a wavelength of 365 nm.