Flame retardant novolac–bisphthalonitrile structural thermosets

Void-free, thermoset networks prepared from phenolic novolacs cured with bisphthalonitrile (BPh) reagents display attractive mechanical, thermal, and fire characteristics. The network properties depend strongly on the novolac–BPh composition. Networks containing 15 wt[percnt] BPh or greater had Tgs above 180 °C and good fracture toughness (K1c∼0.8 MPa m1/2). Cone calorimetry results for an 80:20 (wt/wt) novolac/BPh network, at an incident heat flux of 50 kW/m2, demonstrated a peak heat release rate of 137 kW/m2 and char yields [gt ]50[percnt]. These excellent flame properties are similar to those of phenolic resole networks, which are brittle but known to be flame retardant. re reaction between the novolac and BPh was monitored by the disappearance of the nitrile peak at 2200 cm−1 in the FTIR. The nitrile was ≈90[percnt] consumed after 1 h at 200 °C and ∼20 min at 220 °C. lecular structure of a novolac–BPh crosslink was studied in model reactions using monofunctional phenols. 2-Hydroxydiphenylmethane was reacted with BPh in the melt at 200 °C for 3 h using a 25:1 molar ratio (6.1:1 eq. ratio) of 2-hydroxydiphenylmethane/BPh. FTIR and 1H NMR suggested that the product generated from the model melt reaction contained a diiminoisoindoline structure.