Cross-linked Salen-based polyphosphazenes (Salen-PZNs) enhancing the fire resistance of epoxy resin composites

In this work, two cross-linked Salen-based polyphosphazenes (Salen-PZNs: Salen-PZN-1 microspheres and layered Salen-PZN-2), which contains Salen-Schiff base and phosphazene components, were synthesized. The results showed that the peak heat release rate and total smoke production of 3% Salen-PZN-1/epoxy resin (EP) (3 wt% addition) were reduced by 23.8% and 87.3%, respectively. Meanwhile, after introducing the layered Salen-PZN-2 into EP, efficient flame resistance was obtained. The results of thermogravimetric analysis/infrared spectrometry proved that the harmful gasses of 5% Salen-PZN-1/EP composites were reduced during the combustion. The possible flame retardancy mechanism was considered to be the synergy of phosphate group catalysis, release of nitrogen-containing noncombustible gasses and gas phase quenching. Therefore, this work provides a method for preparing polymers with highly efficient flame-retardant properties.