Resveratrol-based tri-functional benzoxazines: Synthesis, characterization, polymerization, and thermal and flame retardant properties

A series of thermally stable resveratrol-based tri-functional benzoxazine resins have been synthesized using resveratrol, different amines (aniline, 4-chioroaniline and 3-aminophenylacetylene) and paraformaldehyde. The molecular structures of these benzoxazines have been characterized by H-1 and C-13 NMR spectroscopy and FT-IR spectroscopy. The assignments for the characteristic protons and carbons in oxazine rings are confirmed using two-dimensional (2D) NMR techniques, including H-1-H-1 NOESY and H-1-C-13 HMQC. Moreover, the ring-opening polymerization of benzoxazines is studied using in situ FT-IR and differential scanning calorimetry (DSC), and the thermal stability and the flammability of the polybenzoxazines are also investigated by thermogravimetric analysis (TGA) and micro-scale combustion calorimetry (MCC), respectively. In addition to the advantages of lowest melting and polymerization temperatures amongst these resveratrol-based, tri-functional benzoxazines, the corresponding polybenzoxazine derived from benzoxazine containing acetylene shows highest thermal stability with a Tg temperature higher than 350 degrees C, initial degradation temperature at 10% weight loss at 465 degrees C, and char yield of 74% at 800 degrees C in nitrogen atmosphere. Furthermore, this polybenzoxazine also exhibits exceptionally low heat release capacity (30.7 J g(-1) K-1) and total heat release value (6.0 kJ/g).