High-performance flame-retardant PET copolyesters enabled by hydrogen-bonding and phosphorus-nitrogen synergism

Polyethylene terephthalate (PET) is a versatile polymer widely used in firefighting uniforms, engineering plastics, and photovoltaic backplanes, all of which demand high flame retardance. However, achieving a balance between flame retardancy, integrated high mechanical properties, and crystallization capability remains a significant challenge. In this work, we propose an efficient strategy to synthesize inherently flame-retardant, easily crystallizable PET copolyesters with enhanced strength and glass transition temperature ( T g ) by incorporating a phenylphosphorylethyl-benzimidazole-containing monomer (CMP) via chemical copolymerization. With only 5 mol% CMP, the resulting PET-CMP5 copolyester exhibits a significantly improved tensile strength of 67.4 MPa, an elevated T g of 90 °C, a high limiting oxygen index of 33 %, and UL-94 V-0 rating with mitigated dripping behavior. The benzimidazole groups in CMP contribute to a hydrogen-bonding network in PET-CMP copolyester that improves heat resistance and mechanical properties. Simultaneously, the phosphorus-nitrogen synergistic effect in both gas and condensed phases of the CMP unit ensures excellent flame retardance, reduced heat release, and effective melt-dripping suppression. By redesigning the macromolecular chain structure, this work offers a new perspective for developing polymer materials that combine advanced performance with superior fire safety.