Synthesis of an intrinsically flame retardant bio-based benzoxazine resin

An intrinsically flame retardant bio-based benzoxazine (diphenolic acid pentaerythritol caged phosphate benzoxazine, DPA-PEPA-Boz) monomer was synthesized from bio-based diphenolic acid (DPA) using a four-step process. The monomer of DPA-PEPA-Boz was characterized by FT-IR, H-1 NMR and C-13 NMR. The curing behavior of DPA-PEPA-boz was studied and compared with those of DPA based benzoxazine (DPA-Boz) and DPA ester derivative (MDP) based benzoxazine (MDP-Boz) without PEPA by means of non-isothermal differential scanning calorimetry. The results indicated that DPA-PEPA-Boz system showed a two-stage curing, assigned to the exothermic opening reactions of oxazine rings and P-O-C ring in PEPA respectively, while the DPA-Boz and MDP-Boz showed a one-stage curing. In addition, the effect of the introduction of PEPA on thermal and inflammable properties of the resin was evaluated. The residual char of the cured DPA-PEPA-Boz (P-DPA-PEPA-Boz) after 400 degrees C was much higher than those of cured DPA-Boz (P-DPA-Boz) and cured MDP-Boz (P-MDP-Boz) under nitrogen and air atmospheres. Meanwhile, total heat release (THR), peak heat release rate (PHRR) and heat release capacity (HRC) of P-DPA-PEPA-Boz were about half of those of P-DPA-Boz and P-MDP-Boz. P-DPA-PEPA-Boz had a limiting oxygen index (LOI) of 33.5% and achieved V0 rating in UL94 test. P-DPA-PEPA-Boz behaved as a very good intrinsic thermal and flame retardant bio-based benoxazine resin. (C) 2016 Elsevier Ltd. All rights reserved.