Reactive P-N PIN FR for polyester

A 1-vinylimidazole phosphite salt, reacted into unsaturated polyester resin @ 15% achieved UL 94 V-0 (3.2 mm), and over 60% reductions in peak heat release rate and smoke production. 1-vinylimidazole was reacted with phosphorus acid at a 2:1 ratio in ethanol to produce the phosphite salt. This was then reacted into unsaturated polyester resin during curing at 10%, 15% and 20% loadings. The phosphite salt covalently reacts into and cross-links the polyester resin. With 15% phosphite salt loading, UL 94 V-0 (3.2 mm) is achieved, limiting oxygen index (LOI) is increased by around -50% (compared to neat polyester) and peak heat release rate (PHRR) and smoke production are both reduced by more than -60%. This loading of the phosphite salt did not significantly deteriorate the polyester mechanical performance (bending strength -10%, bending modulus not significantly changed, impact strength improved.

“Flame retardancy and smoke suppression of unsaturated polyester resins enabled by 1-vinylimidazole phosphite salts”, W-L Mu et al., Polymer Degradation and Stability 238, 2025, 111353, https://doi.org/10.1016/j.polymdegradstab.2025.111353