'Honeycomb-like' triazine-based covalent organic framework derivative for remarkably improving both flame retardancy and mechanical properties of epoxy resin

In this work, a new triazine-based covalent organic framework (COF) was synthesized and further modified by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to obtain a 'honeycomb-like' DOPO@COF material, which was used as flame retardant (FR) for epoxy resin (EP). Surprisingly, DOPO@COF overcomes the ineffective effect of DOPO on smoke release inhibition and the weak flame retardancy of COF. DOPO@COF can exhibit suppression of smoke and harmful gases while effectively reducing heat release. When incorporating 3 wt% of DOPO@COF into the EP (0.2 wt% phosphorus content), significant reductions of 39.0% in peak heat release rate (pHRR), 18.7% in total heat release rate (THR), 20.6% in peak CO production rate (pCOPR), and 38.7% in peak CO2 production rate (pCO2PR) were observed. Moreover, the introduction of DOPO@COF effectively enhances the storage modulus, crosslinking density and the tensile and impact strength of EP composite. This work provides a new research idea for the development of N, P synergistic EP FRs for nanomaterials based on DOPO and triazine-based COFs.