A Thiophene Derivative Containing N, P and S as Co‐Curing Agent for Flame‐Retardant Epoxy Thermoset

ABSTRACT Although many flame retardants have been synthesized for bisphenol A diglycidyl ether (DGEBA), those with high flame retardancy remain scarce. In this study, the flame retardant of 6,6',6''‐((pyrimidine‐2,4,6‐triyltris(azanediyl))tris(thiophen‐2‐ylmethylene))tris(dibenzo[c,e][1,2]oxaphosphinine 6‐oxide) (TTD) containing N, P and S has been successfully synthesized from 2,4,6‐triaminopyrimidine, 2‐thiophenecarboxaldehyde and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide, and characterizations of FTIR and 1 H and 31 P NMR confirm its chemical structure. The flame‐retardant epoxy resin (EP/DDM/TTD) is prepared by blending DGEBA, TTD, and 4,4’‐diaminodiphenylmethane (DDM). Among all EP/DDM/TTD formulations, EP/DDM/TTD12.5 achieves a V‐0 rating and 39.4% LOI, indicating TTD has high flame retardancy. Meanwhile, EP/DDM/TTD12.5 shows 24.0% and 23.2% lower THR and TSP than EP/DDM, respectively. EP/DDM/TTD7.5 has 40.98% and 38.82% higher tensile and flexural strength than EP/DDM, respectively. TTD's flame retardant mechanism is studied via various characterizations. Various characterizations of char residue of EP/DDM and EP/DDM/TTD12.5 indicate that TTD has a flame‐retardant effect on DGEBA in the condensed phase. Meanwhile, PY‐GC‐MS analysis of TTD's pyrolysis behavior reveals that TTD also exerts a flame‐retardant effect on DGEBA in the gaseous phase. This work opens up possibilities for the application of DGEBA in fields requiring high flame‐retardant performance.