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Polybenzimidazole (PBI) is a heterocyclic polymer whose main chain contains benzimidazole repeating units and adopts a ladder-like structure.The benzene rings and benzimidazole units in its main chain exhibit extremely high rigidity, while the N–H groups on the imidazole rings form intermolecular hydrogen bonds, further enhancing intermolecular interactions.

Owing to the high rigidity of its molecular chains and strong intermolecular interactions, PBI exhibits excellent heat resistance.
With a thermal decomposition temperature exceeding 600 °C, a heat deflection temperature of 435 °C, and a glass transition temperature of 418 °C, PBI is an amorphous engineering resin with outstanding thermal resistance.

Polybenzimidazole has a wide range of applications in aerospace, defense, battery manufacturing, semiconductors and many other fields.

Polybenzimidazole (PBI) was used in a variety of applications for the U.S. space program, including flight suits and other protective clothing, webbings, straps, and tethers. Research in raw materials and process development continued, along with applications development, during the 1960s and 1970s.
In 1983, commercial production of PBI fiber commenced. Today, PBI fiber has been used successfully in firefighters gear, industrial protective clothing, fire-blocking layers for aircraft seats, braided pump packings, and other high-performance products. Research has continued to develop other forms of PBI.