Fire-resistant propargyl ether networks derived from bio-based hydroxycinnamic acids†

Abstract

Three bio-based propargyl ether thermosetting resins with trans-stilbene cores were synthesized from p-coumaric (CD), ferulic (FD), and sinapic (SD) acid, respectively. Differential scanning calorimetry (DSC) analysis of these materials indicated modest processability due to high melting points, short processing windows and large exotherms. To address this issue, a fourth resin with a more flexible bridging group (TD) was synthesized from p-coumaric acid and used as a blending agent. In parallel, CD was photochemically isomerized to the cis-isomer (PD) and blends of CD:PD were prepared. Cross-linked networks derived from the resins exhibited glass transition temperatures (T_gs) ranging from 285–330 °C (storage modulus) and char yields from 27–59% at 1000 °C under N₂. The processable resin blends exhibited exceptional thermal stability due to a higher degree of cross-linking enabled by the structural diversity of the blends. The fire resistance of the networks was evaluated through microscale combustion calorimetry. The networks exhibited heat release capacity (HRC) values ranging from 43–103 J g⁻¹ K⁻¹, which classified them as either non-ignitable or self-extinguishing materials. The results demonstrate that abundant, bio-based hydroxycinnamic acids can serve as platform chemicals for the preparation of thermally stable, fire-resistant networks for aerospace applications.