A benzo five-membered heterocyclic rigid chain polymer containing two nitrogen atoms. It is generally made by aromatic polyamine and diphenyl phthalate through polycondensation and cyclization. The reaction can be carried out in a molten state or in a strong polar solvent. The thermal stability of aromatic PBI in nitrogen is more than 500 ℃. The introduction of flexible groups or side groups can improve the solubility, but the thermal stability is reduced. Trade name Celazole PBI. Poly m-phenylene bibenzimidazole plastic has a thermal deformation temperature of 430 ° C, a limiting oxygen index of 58, a compressive strength of 410 MPa, a tensile strength of 165 MPa, a flexural strength of 227 MPa, a friction coefficient of 0.27 with steel, a dielectric constant of 3.3, radiation resistance, Excellent resistance to boiling water, solvents and chemicals. It can be used as high-temperature-resistant adhesives and high-performance composite materials. It is widely used in aerospace, chemical machinery, petroleum mining, automobiless and other fields, and fiber fabrics are used as protective clothing against fire and atomic radiation.