PIN FRs for unsaturated polyester resins

Various experimental phosphorus PIN FRs were tested in UPR, looking at solid and gas phase action and P oxidation state. In Chu, 2022, three polymeric glycerol-DOPO-based phosphorus compounds were tested in UPR (unsaturated polyester resin), with one achieving, with 15% loading (2.5% P loading), UL-94 V-0 (3 mm) and 29% LOI (limiting oxygen index, compared to 23.5% for neat UPR). The better fire performance between the three molecules was considered to result from better gas phase action, with all three molecules acting effectively in the sold phase (char formation). These molecules included phosphorus with oxidation state +5 (same oxidation state as in phosphoric acid and natural P molecules such as DNA) – see article on P oxidation states below.

“An insight into the effects of the low oxidation states of phosphorous on the combustion behavior of intrinsically flame-retardant unsaturated polyester resins”, Y-D Hu et al., Polymer Degradation and Stability 232 (2025), 111156 https://doi.org/10.1016/j.polymdegradstab.2024.111156