At present, developing a flame-retardant unit to solve the flammability and melt-dripping of poly(ethylene terephthalate) (PET) still is a key issue. To endow PET with good flame retardancy and low smoke releasing, a third monomer, N, N′-bis(2-hydroxyethyl)-biphenyl-3,4,3′,4′-tetracarboxylic diimide (BPDI) containing biphenyl biimide and without any traditional flame-retardant elements, is synthesized and incorporated to the main chain of PET to obtain the P(ET-co-BP)_n copolyester via melt polymerization. The thermal stability, combustion and pyrolysis behaviors of the obtained copolyesters have been well investigated. Thermogravimetric analysis (TGA) results demonstrate that introducing BPDI into PET obviously improves its thermal stability and the forming ability of char residue. LOI, vertical UL-94 and cone calorimeter measurements have been applied to investigate the combustion behaviors of P(ET-co-BP)_n. The results prove that P(ET-co-BP)_n copolyesters containing biphenyl biimide show better fire safety, reflected by lower fire growth rate (FIGRA) and low smoke production. SEM and Raman results suggest that the char layers of P(ET-co-BP)_n become denser and mainly consist of polyaromatic species with small and uniform microstructures. The pyrolysis behaviors of the copolyesters are investigated by Py-GC/MS, and the results showed that the biphenyl biimide structure units can lead to rearrangement reactions at high temperature, ultimately forming the phenanthrene ring structures during combustion. Without traditional flame-retardant elements like halogen and phosphorus, this novel PET copolyester is environmentally friendly and more safety.

目前，开发阻燃单元以解决聚对苯二甲酸乙二醇酯（PET）的易燃性和熔滴问题仍然是关键问题。为了赋予PET良好的阻燃性和低烟气释放性，第三种单体N，N'-双（2-羟乙基）-联苯-3,4,3'，4'-四羧酸二酰亚胺（BPDI）含有联苯基联酰亚胺，不含可以合成任何传统的阻燃元素并将其结合到PET的主链中以获得P（ET-co-BP）_n共聚聚酯通过熔融聚合。已经很好地研究了所得共聚酯的热稳定性，燃烧和热解行为。热重分析（TGA）结果表明，将BPDI引入PET明显改善了其热稳定性和炭渣的形成能力。LOI，垂直UL-94和锥形量热仪测量已用于研究P（ET-co-BP）_n的燃烧行为。结果证明，含有联苯联酰亚胺的P（ET-co-BP）_n共聚酯表现出更好的防火安全性，这是由较低的火灾增长率（FIGRA）和低烟产生所反映的。SEM和拉曼光谱结果表明P（ET-co-BP）_n的炭层变得更致密，主要由具有小而均匀的微观结构的多芳族物质组成。通过Py-GC / MS对共聚酯的热解行为进行了研究，结果表明，联苯联酰亚胺结构单元可以导致高温下的重排反应，最终在燃烧过程中形成菲环结构。由于没有传统的阻燃元素，例如卤素和磷，这种新型的PET共聚酯对环境友好且更加安全。