Intrinsic flame retarding and non-dripping liquid crystal polyethylene terephthalate copolyesters for fire safety system

• PET-based liquid crystal copolyester exhibits excellent thermal stabilities, processability, and non-dripping simultaneously. • One-pot melt polycondensation chemistry to synthesize intrinsic flame retardant copolyester. • Intrinsic flame retardant copolyester can maintain excellent triboelectric performance after combustion. The notorious issue of high fire hazards, including the generation of considerable heat and melt dripping, is recognized as the bottleneck of extensive use of polyethylene terephthalate (PET). Although various techniques have been adopted for the fabrication of flame retardant PET, how to address the contradiction of flame retardancy and anti-dripping while maintaining its good processability in an environment-friendly method is still challenging. Hence, we design and prepare an intrinsic flame retardant copolyester based on PET and thermotropic liquid crystalline polymer (PET/TLCPx) via a simple and efficient one-step melt copolymerization to address the above challenges. On the one hand, the mesogen units not only allow copolyesters to show a typical liquid crystalline behavior with excellent processability but also constructs a highly rigid main chain to endow PET/TLCPx with outstanding thermal stability, fire resistance, and non-dripping. Furthermore, the resultant PET/TLCP3 exhibits a much lower (by 72%) peak heat release rate than that of PET, which is attributed to the formation of a denser char layer (char yield ∼37%) for excellent fire resistance. Meanwhile, the melt dripping of PET/TLCPx is suppressed with the increase of complex viscosity and the growth of molecular weight due to the post-condensation during combustion. The resultant high-performance copolyesters are highly valuable for high-end applications that have strict requirements for fire safety and thermal stability, such as fire alarm and rescue systems based on triboelectric effect and shape memory behaviors.