Cardanol-derived polybenzoxazine networks integrated with high glass transition temperatures, flame retardancy and toughness

In this work, diphenolic acid- and furfuryl-based benzoxazine (MDP-FuBz) was synthesized from methyl diphenolic acid (DPA) via the Mannich reaction. The curing temperature of MDP-FuBz was studied via differential scanning calorimetry (DSC). Since the flame retardant effect of MDP-FuBz was not satisfactory after curing, two kinds of phosphorus-containing cardanol-derived benzoxazine monomers (C-BA-DOPOBz and C-BA-diDOPOBz) were synthesized and characterized via Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. C-BA-DOPOBz and C-BA-diDOPOBz were used to endow MDP-FuBz with anti-flammability and toughness. As expected, the addition of 10 wt. % C-BA-DOPOBz or C-BA-diDOPOBz to MDP-FuBz improved the flame retardancy and glass transition temperature of the resulting interpenetrating polybenzoxazine networks. Although C-BA-diDOPOBz showed higher flame retardancy than C-BA-DOPOBz, both MDP-FuBz/10%C-BA-DOPOBz and MDP-FuBz/10%C-BA-diDOPOBz could not reach the UL-94 V-0 rating. C-BA-diDOPOBz was selected to further increase the content to modify MDP-FuBz. With the addition of 30 wt. % C-BA-diDOPOBz, the resulting interpenetrating polybenzoxazine networks reached the UL-94 V-0 rating, and the impact strength of MDP-FuBz/C-BA-diDOPOBz was 43 % higher than that of MDP-FuBz polybenzoxazine. This work presents interpenetrating polybenzoxazine networks consisting of diphenolic acid-based benzoxazine (rigid segment) and cardanol-based benzoxazine (flexible segment), which are integrated with high glass transition temperatures, flame retardancy and toughness.