Phosphorus-Based -Amino Acid Mimetic for Enhanced Flame-Retardant Properties in an Epoxy Resin

This work demonstrates the introduction of a phosphonate moiety into a commonly used curing agent, 4,4-diaminodiphenylmethane (DDM), via an -aminophosphonate. This compound (DDMP) can be prepared and isolated in analytical purity in under 1h and in good yield (71%). Thermoset polymer (epoxy-derived) samples were prepared using a room-temperature standard cure (SC) and a post-cured (PC) protocol to encourage incorporation of the -aminophosphonate into the polymer network, with improved flammability properties observed for the latter. Thermogravimetric analysis under a nitrogen atmosphere showed increased char yield at 600 degrees C, and similar observations were made when analysis was conducted in air. Significant reductions in flammability are observed at very low phosphorus content (P%=0.16-0.49%), demonstrated by higher char yields (25.5 from 14.0% in air), decreased burn time from ignition (60 to 24s), and decreased mass loss after ignition (87.6 to 58.5%). Limiting Oxygen Index for the neat polymer (P%=0%, 20.3 +/- 0.8%) increased with increasing -aminophosphonate additive (P%=0.16%, 20.8 +/- 0.6%; P%=0.32%, 21.4 +/- 0.4%; P%=0.49%, 22.6 +/- 0.8%).