Although polyamide 6 (PA6) is a widely used engineering plastic, its high flammability with severe melt dripping poses significant fire risks, and common additive flame retardants often deteriorate its mechanical properties. Herein, an intrinsic flame-retardant PA6 copolymer was successfully synthesized by incorporating a phosphorus-containing monomer (PD) derived from DOPO and a Schiff base intermediate, and the copolymer was named PA6-co-PDx and was prepared by melt polycondensation. The incorporation of PD significantly enhanced the flame retardancy of PA6, with PA6-co-PD40 passing a UL-94 V-0 rating and a limiting oxygen index of 26.1%. Cone calorimetry revealed remarkable reductions in the peak heat release rate (53.6%) and total heat release (27.6%), indicating suppressed combustion intensity. The flame-retardant mechanism was attributed to the synergistic effect of high-temperature self-cross-linking and catalytic char formation in the condensed phase, along with gas-phase radical quenching by phosphorus-containing species. Although the introduction of PD slightly reduced the crystallinity and mechanical properties, the copolymer retained acceptable processability, demonstrating great potential for applications requiring high flame retardancy.
Zhu et al. (Wed,) studied this question.