A novel naphthalene-boron-silicon phenolic resin and its high-strength thermal insulation aerogel: Structure and thermal pyrolysis kinetics

The development of high-speed aircraft demands phenolic thermal protection materials with superior thermal stability and high char yield, yet achieving this without compromising moderate curing temperatures remains a formidable challenge. Herein, a novel boron–silicon phenolic resin (BSiNR) cured at 165 ℃ was synthesized using 1-naphthaleneboronic acid and vinyltrimethoxysilane. Specifically, the incorporation of rigid naphthalene rings, vinyl crosslinking groups, and high-energy B–O and Si–O bonds enhanced the crosslinked network and promoted ceramic conversion at high temperatures. The cured resin exhibited an initial decomposition temperature of 492.99 ℃ (T_5%) and a char yield of 75.20% (R_1000℃) at 10 ℃·min⁻¹. Pyrolysis kinetic analysis showed that pyrolysis activation energy increased from 329.33 kJ·mol⁻¹ (15–25 ℃·min⁻¹) to 473.72 kJ·mol⁻¹ (50–100 ℃·min⁻¹), indicating the pyrolysis reaction became more difficult under rapid heating conditions. An aerogel (BSiNR-PA) with an adjustable density (0.118–0.301 g·cm⁻³) was fabricated, demonstrating a compressive strength of 29.52 MPa at 30% strain, thermal conductivity of 41.0 mW·m⁻¹·K⁻¹, and pyrolysis activation energy of 238.13 kJ·mol⁻¹. The T_5% and R_1000°C of the aerogel were 416.46 °C and 67.89% at 10 °C·min⁻¹, respectively, along with mass and linear ablation rates of 0.0036 g·s⁻¹ and 0.0065 mm·s⁻¹. The naphthalene-boron-silicon modification strategy enhanced thermal stability, char-forming ability, and mechanical strength of phenolic systems, offering a promising route for next-generation lightweight thermal protection materials.