A branched chain dialkyl phosphinate – dialkyl ammonium PIN FR achieved UL 94 V-0 (1 mm) in polyamide PA6. The macromolecular PIN FR was prepared by reacting a commercial phosphorus containing cyclic acid anhydride (2-Methyl-1,2-oxaphospholan-5-one-2-oxide) with polyethylenimine, at a molar ratio of oxaphosphalane to amine groups of 1:2. The resulting PN FR had a phosphorus content of c. 13%. UL 94 fire testing showed V-0 (1 mm) for polyamide PA6 with 10% of the PN FR, compared to V-0 for 10% of the commercial aluminium-phosphorus PIN FR AlPi, V-2 for 10% melamine cyanurate, APP or red phosphorus and V-2 or NR for only 1% loadings of the different tested FRs. Glow wire test performance is improved from NR (neat PA6, 850°C) to pass with 5% PN FR (even at higher temperature 960°C). Mechanical properties of the polyamide are slightly modified (increased stiffness, reduced elongation at break), extrusion and injection moulding processing are compatible, and electrical resistivity is significantly improved (up to 3 x increase).
“The effect of the presence of a macromolecular organophosphorus flame retardant, poly (N-[3- oxopropyl methylphosphinate] ethyleneimine), on the flammability, thermal stability, and mechanical properties of polyamides”, M. Helmy et al., Fire and Materials. 2022; 1–10, https://doi.org/10.1002/fam.3092