Boron- and Phthalonitrile-Containing Phenol Formaldehydes: Curing, Thermal, and Ablative Performance

In this study, we report a new class of high-performance phenol formaldehyde resin incorporated with both phthalonitrile and boron moieties. The systems possessed excellent thermal stability and char yield (66% to 70%). The radiant lamp test of the resin infused carbon preform composite at a moderate atmospheric re-entry condition heat flux of 54.5 W/cm² exhibited excellent back wall temperature of 316 °C at 560 s confirming its ablative application suitability. The Lewis acid nature of boron compounds can aid in cure acceleration results in early cure initiation of PNB resins and improved processability. Pyrolysis of phthalonitrile incorporated resin systems resulted in high degree of graphitization denoted by decrease in I_D/I_G ratio (0.63–0.67).The formation of B₄C on the surface of the carbonized products was beneficial for improving the thermal stability of the resin at elevated temperatures. The XPS of pyrolyzed systems confirms the B─N bond formation during Lewis acid mediated curing and formation of B₂O₃ and B₄C structures. The activation energy for curing determined by Kissinger and Flynn–Wall–Ozawa methods were nearly same (91–109 kJ/mol). Structural, thermal and ablative properties vindicate that these novel polymers are highly promising candidates as matrix resin for ablative type composite materials.