Cerium–Phosphate Complexes for Intumescent Flame‐Retardant Synergists: Enhancing Fire Safety and Thermostability of <scp>ABS</scp> Resin With Minimal Mechanical Sacrifice

ABSTRACT Acrylonitrile‐butadiene‐styrene (ABS) resin faces significant fire hazards due to inherent flammability, necessitating halogen‐free flame retardants with minimal mechanical compromise. Herein, novel cerium diethylenetriamine penta(methylene phosphonate) (CeDETPMP) complexes were molecularly engineered via hydrothermal synthesis, systematically tuning Ce 3+ ‐to‐ligand ratios (from 1:3 to 3:1) to optimize coordination geometry. At 1 wt% loading, CeDETPMP synergized with an intumescent flame retardant (IFR, 19 wt% ADP/PAPP) to enable ABS composites to achieve UL‐94 V‐0 rating and a limiting oxygen index (LOI) of 24.8%, while reducing peak heat release rate (PHRR) by 73.8% and total smoke release (TSR) by 35.4% in cone calorimetry. Crucially, Ce 3+ /Ce 4+ redox cycling catalyzed graphitized char formation, suppressing crack propagation and enhancing barrier integrity. The optimal CeDETPMP (1:3) and CeDETPMP (3:1) ratios minimized mechanical sacrifice compared to ABS/IFR systems, retaining tensile strength within 26 MPa and 11 kJ/m 2 . This work establishes a structure–property paradigm for rare‐earth synergists in high‐safety polymer engineering.