Development of a DOPO-based flame retardant with pendant chains for enhanced polyurethane elastomers

Abstract

Polyurethane elastomers (PUE) with viscoelastic properties are extensively used in rail transit due to their versatility. However, enhancing their flame retardancy and damping performance remains a challenge, particularly when relying on the introduction of additives. In this work, we synthesized a novel reactive flame retardant, 1,4-bis-DOPO- (1,4-bis(((1‑hydroxy-2-ethylethyl) amino) methyl) benzene) (PABD), which incorporates both phosphorus (P) and nitrogen (N) elements, along with pendant chains. PABD was then used to produce high-performance flame-retardant polyurethane elastomers (PUE-PABD). Flammability testing revealed that PUE-PABD₁₅ achieved excellent flame retardancy, passing the UL-94 V-0 rating with a limiting oxygen index (LOI) of 29.1 %. Compared to that of unmodified PUE, the peak heat release rate and total heat release of PUE-PABD₁₅ were reduced by 82.6 % and 49.5 %, respectively, while the peak smoke production rate and total smoke production were lowered by 70.7 %. The dynamic mechanical analysis showed an increase in tanδmax from 0.39 to 0.74, with the effective damping temperature range broadening from 29.3 °C to 54.1 °C. This improvement was attributed to the pendant chains, which reduced phase separation between hard and soft segments. Moreover, the incorporation of 15.0 wt. % PABD increased the tensile strength of PUE by 108.5 %, which was due to enhanced hydrogen bonding and π-π stacking from the benzene ring groups. This work lays a foundation for the development of high-performance polyurethane materials suitable for advanced rail transit applications.