Synthesis of a caged bicyclic phosphates derived anhydride and its performance as a flame-retardant curing agent for epoxy resins

A novel curing and flame-retardant agent (PEPA-TMAC) was successfully synthesized. The chemical structure was characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Use of PEPA-TMAC as part of the curing agent in combination with another anhydride for a commercial epoxy resin (EP) was studied. Results of differential scanning calorimetry (DSC) indicated that PEPA-TMAC was an effective curing agent for EP. The dynamic mechanical analysis (DMA) results showed that the glass transition temperature (T-g) and cross-linking density (V-e) of EP composites exhibited an increase trend with the addition of PEPA-TMAC. The limiting oxygen index (LOI) value of EP composites reached 26.9%, and the cone calorimeter results indicated that peak heat release rate (PHRR), total heat release (THR), smoke produce rate (SPR), and total smoke produce (TSP) remarkably decreased with increasing PEPA-TMAC content. TGA data showed that the addition of PEPA-TMAC greatly increased the amount of residual char during combustion. The morphology of the residual char was studied by SEM and showed that the addition of PEPA-TMAC greatly increased the stability of EP composites. The thermogravimetric analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), and FTIR results revealed the flame-retardant mechanism that PEPA-TMAC can promote the formation of charred layers with the phospho-carbonaceous complexes in the condensed phase during burning of EP composites.